Abstract:
Peptides are provided having an excellent safety, stability due to relatively low molecular weights thereof, and cell growth promotion, which are different from cell growth factors produced by abnormal cells such as tumor cells. Peptide compositions which are excellent in promoting cell growth containing partial peptides of one or more peptide chains selected from peptide chains forming noncrystalline portions constituting silk protein. The partial peptides have specific amino acid sequences formed of four to forty amino acid residues. This invention has succeeded in providing novel peptides excellent for cell growth by separating and fractionating peptides, having specific amino acid sequences of molecular weights not higher than 10,000, preferably ranging from 4,000 to 400, from the noncrystalline portions of silk protein as well as by synthesizing peptides similar to such peptides. These peptides may be used for biomaterials such as a cell adhesion agent, cell growth-promoting agent, wound healing promoting agent, skin care material like cosmetic material or the like, and cell culture substrate.

Description:
TECHNICAL FIELD 
     The present invention relates to peptides from silk protein which are excellent in promoting cell growth, a production method thereof, and application thereof to the fields of medicaments, quasi drugs, cosmetics, etc., as a material for skin care as well as to cell culture substrates as a biomaterial. 
     RELATED ART 
     Since silk threads have been used as a surgical suture from the old days, silk protein is regarded as a biocompatible material, and new developments focusing attention on this property have recently become active for its new uses in various fields. 
     For example, silk threads are solubilized to form an aqueous silk protein solution, followed by conversion to powder by precipitation, drying, grinding, etc., for additives to cosmetics; the aqueous silk protein solution is made into a film-like material by casting on a plate and the like for a cell culture bed or wound-covering and coating material; and the silk protein solution is made into a gel-like material for use in food and cosmetics. The developments of these uses are pursued. 
     Such developing examples include, for example, Kokai (Jpn. unexamined patent publication) 62-000415, Kokoku (examined patent publication) 01-044320, Kokai (Jpn. unexamined patent publication) 01-254164, Kokoku (examined patent publication) 06-004679, Kokai (Jpn. unexamined patent publication) 11-139986, Kokai (Jpn. unexamined patent publication) 11-276876, U.S. Pat. No. 2,997,758, U.S. Pat. No. 2,990,239, Kokai (Jpn. unexamined patent publication) 11-253155, Patent application 2002-230656, Patent application 2002-148849, Kokai (Jpn. unexamined patent publication) 2001-163899. (See patent literatures from 1 to 12) 
     During the development of new silk materials, it has become apparent that silk protein possesses various functions such as cell growth promotion, antioxidation, germicidal action, alcohol digestion and anticoagulation of blood. 
     However, it has not yet been elucidated which site or structure in silk protein is responsible for those functions. 
     The present inventors paid attention to the cell growth function associated with silk protein and have pursued the development and study of its function with the aim of utilizing cocoon filaments or silk threads as a skin care material for wound-covering materials, cosmetics and improved materials of synthetic fiber after these threads are solubilized and then converted into powder, film, gel and the like (for example, see patent literatures 8, 9, 10, 11 and 12). 
     In the course of the above development and study, it was found that the H and L-chains of fibroin and sericin, components constituting silk protein, have a growth-promoting action on fibroblasts originating from normal human skin (for example, see patent literatures 13, 14, and 15). 
     On the other hand, cocoon filaments are used as a fiber, besides the field of clothing, in the fields of, for example, medical care (surgical suture for surgery), cosmetics (puff) and the like by processing cocoons via various process steps into raw silk and further into silk fabrics, and it has recently been recognized that the molecular weight of silk protein decreases during the processing of cocoon and raw silk. 
     Moreover, also in the process step of converting cocoon filaments or silk threads into powder, film, gel or the like (particularly, the solubilizing step of cocoon filaments or silk threads), the molecular weight of silk protein was found to decrease (H. Yamada et al., Material Science &amp; Engineering C, 14, p. 41–46 (2001)), (Tubouchi Kouzou, Yamada Hiromi, Takasu Yoko: the Japanese Society of Sericulture Science academic journal, Vol. 71, no. 1, P. 1–5 (2002)), (See nonpatent literature, nonpatent literature 2). 
     Silk proteins with their molecular weight decreased by such processes show a broad band with a smear in a molecular weight range between 10,000 and 200,000 daltons on an electrophoretogram. 
     Those with a molecular weight of less than 10,000 daltons are mostly removed during the steps of dialysis and the like, and in fact, their molecular weights are decreased up to amino acid and oligopeptide levels. 
     The silk proteins with lowered molecular weights were found to have a reduced growth-promoting activity for human cells or to inhibit the cell growth (see patent literature 11). 
     In other words, undegraded fibroin and undegraded sericin are excellent for promoting cell growth, whereas complex and heterogeneous cleavage of peptide bonds by treatment with an acid, alkali, light, heat, etc., during the processing of the cocoon resulted in inhibiting cell growth along with a reduction in their molecular weights. 
     Accordingly, for the purpose of utilizing the cell growth-promoting function of silk proteins, it is preferred to use undegraded fibroin or undegraded sericin, fibroin H-chain (molecular weight, ca. 350,000) or L-chain, sericin a (molecular weight, ca. 400,000) and the like in their undegraded states. 
     However, these three components (particularly, the H-chain and sericin a) have large molecular weights, and their stability in keeping their properties constant during prolonged storage is low. 
     Further, the L-chain is contained in fibroin only at less than 10% by weight and is small in quantity. 
     Furthermore, there is yet no report clarifying which portion of each of these three components possesses cell growth-promoting activity. 
     Patent Literature 1 
     
         
         Kokai (Jpn. unexamined patent publication) 62-000415
 
Patent Literature 2
 
         Kokoku (examined patent publication) 01-044320
 
Patent Literature 3
 
         Kokai (Jpn. unexamined patent publication) 01-254164
 
Patent Literature 4
 
         Kokai (Jpn. unexamined patent publication) 04-202435
 
Patent Literature 5
 
         Kokoku (examined patent publication) 06-004679
 
Patent Literature 6
 
         Kokai (Jpn. unexamined patent publication) 11-139986
 
Patent Literature 7
 
         Kokai (Jpn. unexamined patent publication) 11-276876
 
Patent Literature 8
 
         U.S. Pat. No. 2,997,758
 
Patent Literature 9
 
         U.S. Pat. No. 2,990,239
 
Patent Literature 10
 
         Kokai (Jpn. unexamined patent publication) 11-253155
 
Patent Literature 11
 
         Patent application 2002-230656
 
Patent Literature 12
 
         Patent application 2002-148849
 
Patent Literature 13
 
         Kokai (Jpn. unexamined patent publication) 2001-163899
 
Patent Literature 14
 
         Patent application 2001-180169
 
Patent Literature 15
 
         Kokai (Jpn. unexamined patent publication) 2002-128691
 
Nonpatent Literature 1
 
         H. Yamada et al., Materials Science &amp; Engineering C, 14, P. 41–46 (2001)
 
Nonpatent Literature 2
 
         Tsubouchi Kouzou, Yamada Hiromi, Takasu Yoko: The Japanese Society of Sericulture Science academic journal Vol. 71, No. 1, P. 1–5 (2002)
 
Nonpatent Literature 3
 
         Tashiro Yutaka and Otsuki Eiichi, Journal of Cell Biology, Vol. 46, P1 (1970) 
       
    
     The fibroin H-chain and the a component of sericin are excellent for promoting cell growth, while they have high molecular weights larger than 300,000 and tend to crystallize. 
     In comparison to these, the molecular weight of the fibroin L-chain is 25,000 and smaller than that of the H-chain or the a component, but it has a tendency to crystallize more easily than ordinary proteins. 
     In addition, the ratio of fibroin H-chain to L-chain by weight is about 13 (H-chain) to 1 (L-chain), and the percentage of the L-chain is very small. 
     Proteins having a high molecular weight and high crystallinity are unstable in aqueous solutions. 
     Furthermore, when medicaments or cosmetic additives containing an oily ingredient or the like are added to these proteins, gel formation may readily occur, turning to unstable physical properties, and their stability during prolonged storage (more than 1 year) is low. 
     On the other hand, substances which have a molecular weight lower than silk fibroin H-chain or sericin a and are excellent for cell growth include growth factors for various cells, for example, fibroblast growth factor (FGF) having a molecular weight ranging from 17,700 to 19,000. 
     These factors are secreted from tumors and cancerous cells, or from rapidly growing cells, and some of them are used as a therapeutic agent for skin ulcer (Fiblast Spray, Kaken Pharmaceutical Co., Ltd.), but their safety is a concern. 
     SUMMARY OF THE INVENTION 
     The present invention was accomplished to solve these problems. 
     Namely, an object of this invention is to obtain peptides having excellent safety, stability due to their relatively low molecular weights, and cell growth promotion, all of which are different from cell growth factors produced by abnormal cells such as tumor cells. 
     In order to solve the above problems, the present inventors have diligently conducted research and succeeded now in identifying that peptide chains located at specific sites of silk fibroin have a cell growth-promoting function, thus completing the present invention. 
     That is, the present invention is significant in the aspect (1) that peptide compositions excellent for promoting cell growth comprise partial peptides of one or more peptide chains selected from peptide chains forming noncrystalline portions constituting silk protein, where the partial peptides have specific amino acid sequences formed of four to forty amino acid residues. 
     More specifically, the present invention provides peptide compositions excellent for promoting cell growth comprising the partial peptides from one or more peptide chains selected from the respective peptide chains of the N-terminal portion (I), the noncrystalline portion (A) and the C-terminal portion (a) constituting the H-chain of silk fibroin from a domesticated silkworm, the peptide chain of the L-chain thereof, and the respective peptide chains of the N-terminal portion (I), noncrystalline portion (A) and C-terminal portion (a) constituting the silk fibroin from a wild silkworm belonging to the genus  Antheraea  such as  Antheraea yamamai , where the partial peptides have specific amino acid sequences formed of 4 to 40 amino acid residues. 
     Further, a second aspect (2) provides a peptide composition where the peptide chains with the above specific amino acid sequences have any of the following amino acid sequences from (1) to (8): 
     
       
         
               
               
               
               
               
             
           
               
                 (1) 
                 A-6-2 
                 Val Ile Thr Thr Asp Ser Asp Gly Asn Glu 
                 (SEQ ID NO. 1) 
                   
               
               
                   
                   
                                 5                   10 
               
               
                   
               
               
                 (2) 
                 A-6-6 
                 Asn Ile Asn Asp Phe Asp Glu Asp 
                 (SEQ ID NO. 2) 
               
               
                   
                   
                                 5 
               
               
                   
               
               
                 (3) 
                 SfHe 
                 Ala Ala Ser Ser Val Ser Ser Ala Ser Ser Arg Ser Tyr Asp Tyr Ser Arg Arg Asn 
                 (SEQ ID NO. 3) 
               
               
                   
                   
                                 5                   10                  15 
               
               
                   
               
               
                   
                   
                 Val Arg Lys Asn 
               
               
                   
                   
                 20 
               
               
                   
               
               
                 (4) 
                 SfHA 
                 Gly Ser Ser Gly Phe Gly Pro Tyr Val Ala His Gly Gly Tyr Ser Gly Tyr Glu Tyr 
                 (SEQ ID NO. 4) 
               
               
                   
                   
                                 5                   10                  15 
               
               
                   
               
               
                   
                   
                 Ala Trp Ser Ser Glu Ser Asp Phe Gly Thr 
               
               
                   
                   
                 20                  25 
               
               
                   
               
               
                 (5) 
                 AfH1 
                 Tyr Gly Trp Gly Asp Gly Gly Tyr Gly Ser Asp Ser 
                 (SEQ ID NO. 5) 
               
               
                   
                   
                                 5                   10 
               
               
                   
               
               
                 (6) 
                 AfH5 
                 Asp Glu Tyr Val Asp Asn 
                 (SEQ ID NO. 6) 
               
               
                   
                   
                                 5 
               
               
                   
               
               
                 (7) 
                 AfH6 
                 Val Glu Thr Ile Val Leu Glu Glu Asp Pro Tyr Gly His Glu Asp Ile Tyr Glu Glu 
                 (SEQ ID NO. 7) 
               
               
                   
                   
                                 5                   10                  15 
               
               
                   
               
               
                   
                   
                 Asp 
               
               
                   
                   
                 20 
               
               
                   
               
               
                 (8) 
                 AfH7 
                 Asp Asp Gly Phe Val Leu Asp Gly Gly Tyr Asp Ser Glu 
                 (SEQ ID NO. 8) 
               
               
                   
                   
                                 5                   10 
               
             
          
         
       
     
     Still further, a third aspect (3) provides a peptide excellent for promoting cell growth containing any of the following amino acid sequences from (1) to (8): 
     
       
         
               
               
               
               
               
             
           
               
                 (1) 
                 A-6-2 
                 Val Ile Thr Thr Asp Ser Asp Gly Asn Glu 
                 (SEQ ID NO. 1) 
                   
               
               
                   
                   
                                 5                   10 
               
               
                   
               
               
                 (2) 
                 A-6-6 
                 Asn Ile Asn Asp Phe Asp Glu Asp 
                 (SEQ ID NO. 2) 
               
               
                   
                   
                                 5 
               
               
                   
               
               
                 (3) 
                 SfHe 
                 Ala Ala Ser Ser Val Ser Ser Ala Ser Ser Arg Ser Tyr Asp Tyr Ser Arg Arg Asn 
                 (SEQ ID NO. 3) 
               
               
                   
                   
                                 5                   10                  15 
               
               
                   
               
               
                   
                   
                 Val Arg Lys Asn 
               
               
                   
                   
                 20 
               
               
                   
               
               
                 (4) 
                 SfHA 
                 Gly Ser Ser Gly Phe Gly Pro Tyr Val Ala His Gly Gly Tyr Ser Gly Tyr Glu Tyr 
                 (SEQ ID NO. 4) 
               
               
                   
                   
                                 5                   10                  15 
               
               
                   
               
               
                   
                   
                 Ala Trp Ser Ser Glu Ser Asp Phe Gly Thr 
               
               
                   
                   
                 20                  25 
               
               
                   
               
               
                 (5) 
                 AfH1 
                 Tyr Gly Trp Gly Asp Gly Gly Tyr Gly Ser Asp Ser 
                 (SEQ ID NO. 5) 
               
               
                   
                   
                                 5                   10 
               
               
                   
               
               
                 (6) 
                 AfH5 
                 Asp Glu Tyr Val Asp Asn 
                 (SEQ ID NO. 6) 
               
               
                   
                   
                                 5 
               
               
                   
               
               
                 (7) 
                 AfH6 
                 Val Glu Thr Ile Val Leu Glu Glu Asp Pro Tyr Gly His Glu Asp Ile Tyr Glu Glu 
                 (SEQ ID NO. 7) 
               
               
                   
                   
                                 5                   10                  15 
               
               
                   
               
               
                   
                   
                 Asp 
               
               
                   
                   
                 20 
               
               
                   
               
               
                 (8) 
                 AfH7 
                 Asp Asp Gly Phe Val Leu Asp Gly Gly Tyr Asp Ser Glu 
                 (SEQ ID NO. 8) 
               
               
                   
                   
                                 5                   10 
               
             
          
         
       
     
     Still further, a fourth aspect (4) provides a method of separating and obtaining peptides which are excellent in promoting cell growth from the noncrystalline portions by hydrolysis of undegraded silk protein from a domesticated silkworm or degraded silk fibroin from a wild silkworm belonging to the genus  Antheraea , and by subsequent molecular fractionation. 
     Still further, a fifth aspect (5) provides a method of separating and obtaining peptides which are excellent in promoting cell growth from the noncrystalline portions in the above fourth invention wherein the hydrolysis is conducted by using a dilute acid, hydroxylamine or a protease. 
     Still further, sixth (6) and seventh (7) aspects provide a cell growth-promoting agent containing the peptide compositions described in the above (1) and (2) and the peptides described in the above (3). 
     Still further, eighth (8) and ninth (9) aspects provide a cell adhesion agent containing the peptide compositions described in the above (1) and (2) and the peptides described in the above (3). 
     Still further, tenth (10) and eleventh (11) aspects provide a wound healing promoting agent containing the peptide compositions described in the above (1) and (2) and the peptides described in the above (3). 
     Still further, twelfth (12) and thirteenth (13) aspects provide a cosmetic material containing the peptide compositions described in the above (1) and (2) and the peptides described in the above (3). 
     Still further, fourteenth (14) and fifteenth (15) aspects provide a cell culture substrate containing the peptide compositions described in the above (1) and (2) and the peptides described in the above (3). 
     This invention has succeeded in providing novel peptides which are excellent in cell growth and have specific amino acid sequences of molecular weights lower than 10,000, preferably ranging from 4,000 to 400, by separating and fractionating peptides from the noncrystalline portions of silk protein as well as by synthesizing peptides similar to such peptides. 
     These peptides may be used as biomaterials such as a cell adhesion agent, cell growth-promoting agent, wound healing promoting agent, material for skin care, like a cosmetic, etc., and cell culture substrate. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The peptides from the noncrystalline portions of silk protein which are excellent in promoting cell growth and the peptide compositions thereof have been obtained by the following procedures and also been determined for their amino acid sequences.
     (1) Cocoon layer from a wild silkworm belonging to the genus  Antheraea , such as domesticated silkworm or  Antheraea yamamai , is degummed, then solubilized in an aqueous solution of LiSCN and centrifuged. The separated supernatant is recovered and dialyzed against water. The dialyzate is again centrifuged and the separated supernatant is recovered.   (2) To the purified supernatant which has been separated and recovered, a protease such as chymotrypsin is added and treated for hydrolysis.   (3) The supernatant (noncrystalline portion) of the solution after the hydrolysis treatment is separated from the precipitate layer (crystalline portion) and recovered.   (4) The supernatant (noncrystalline portion) is fractionated by reverse phase chromatography.   (5) Each fraction fractionated by the reverse phase chromatography is subjected to cell culturing.   (6) The fraction which is excellent in cell growth is fractionated by molecular weight by means of gel filtration chromatography, and fractions (peptide chains) having a cell growth rate 2-fold higher than that of a control fraction are determined for their amino acid sequences.   (7) Peptides expected to show excellent cell growth promotion are designed and synthesized based on the obtained peptide.   

     Thus, the present invention can allow separation and fractionation of peptides of molecular weights lower than 10,000, preferably ranging from 4,000 to 400, having excellent cell growth-promoting activity from the noncrystalline portions of silk protein, synthesis of peptides analogous to such peptides, and provision of these peptides as biomaterials, such as cell adhesion agents, cell growth-promoting agents, wound healing promoting agents, materials for skin care like cosmetics, etc., and cell culture substrates. 
     The cell growth-promoting peptides originating from silk protein of the present invention mean the peptides which show a cell growth rate 2-fold higher than that of a control in which cells are cultured in the absence of an added peptide in the three-day cell culture test as described in Examples 1 to 3. 
     Primary Structure of Fibroin from Domesticated Silkworm 
     In the case of domesticated silkworm, the silkworm spins silk protein at the time of spinning to spin a cocoon (composed of cocoon filament and a pupa). In the cocoon filament, there exist fibroin at its center and sericin at its periphery, and their existing ratio is known to be 70 to 80% (fibroin) to 20 to 30% (sericin). 
     Fibroin in cocoon filament (silk protein refers to a combination of fibroin and sericin or each individually) is ca. 370,000 in its molecular weight. 
     (Tasiro Yutaka and Otsuki Eiichi, Journal of Cell Biology, Vol, 46, P1 (1970)) (See non-patent literature 3) 
     In fibroin having a molecular weight of ca. 370,000, molecules having a size of ca. 350,000 (H-chain) and a size of ca. 25,000 (L-chain) are bound to each other via an S—S bond. 
     The fibroin H-chain has a very high molecular weight, while it is composed of repeating analogous sequences of amino acid residues. 
     According to Gen Bank accession no. AF 226688, the precursor protein of the H-chain is composed of the N-terminal portion (I), the repetitive part of a crystalline portion (R) and a noncrystalline portion (A), and the C-terminal portion (a). 
     The repetitive part is repeated by twelve crystalline portions (from R01 to R12) through the mediation of eleven noncrystalline portions (from A01 to A11) therebetween. 
     The crystalline portions are composed of a long repetition of a highly crystalline dipeptide (Gly-X). X is highly crystalline Ala or additionally Ser as the main component, and other minor components thereof include Tyr, Val, and the like. 
     In particular, the repetition of Gly Ala Gly Ala Gly Ser or Gly Ala is abundant. 
     As the result, the sum of Gly and Ala in the crystalline portion exceeds 50% and amounts to more than ca. 70%. 
     The peptides of A01 to A11 in the noncrystalline portions are similar to one another in their amino acid sequences, while small differences are found in each amino acid sequence. 
     Further, the sum of Gly and Ala in each noncrystalline portion (from A01 to A11) is less than 50%. 
     The N-terminal portion and the C-terminal portion are considered to be noncrystalline from their amino acid sequences and amino acid compositions, and similarly to A01 to A11, the sum of Gly and Ala is each less than 50%. 
     On the other hand, there exist some portions in which the sum of Gly and Ala exceeds 50% in partial peptides of ca. 6 to 10 residues within the noncrystalline portions. 
     &lt;Precursor of Fibroin H-Chain&gt; 
     
         
         I-R01A01R02A02R03A03R04A04R05A05R06A06R07A07R08A08R09A09R10A10R11A11R12-a
 
N-Terminal Portion: I
 
       
    
     N-terminal portion (I) is the initial peptide portion and its amino acid sequence is as follows: 
                             Met Arg Val Lys Thr Phe Val Ile Leu Cys Cys Ala Leu Gln   (SEQ ID NO. 9)                           5                   10               Tyr Val Ala Tyr Thr Asn Ala Asn Ile Asn Asp Phe Asp Glu       15                  20                  25               Asp Tyr Phe Gly Ser Asp Val Thr Val Gln Ser Ser Asn Thr           30                  35                  40               Thr Asp Glu Ile Ile Arg Asp Ala Ser Gly Ala Val Ile Glu               45                  50                  55               Glu Gln Ile Thr Thr Lys Lys Met Gln Arg Lys Asn Lys Asn                   60                  65                  70               His Gly Ile Leu Gly Lys Asn Glu Lys Met Ile Lys Thr Phe                       75                  80               Val Ile Thr Thr Asp Ser Asp Gly Asn Glu Ser Ile Val Glu       85                  90                  95               Glu Asp Val Leu Met Lys Thr Leu Ser Asp Gly Thr Val Ala           100                 105                 110               Gln Ser Tyr Val Ala Ala Asp Ala Gly Ala Tyr Ser Gln Ser               115                 120                 125               Gly Pro Tyr Val Ser Asn Ser Gly Tyr Ser Thr His Gln Gly                   130                 135                 140               Tyr Thr Ser Asp Phe Ser Thr Ser Ala Ala Val                       145                 150            
Crystalline Portion: R01, R02, . . . , R12
 
     All of R01, R02, . . . R12 are portions called crystalline portion, and the number of amino acid residues is more than 300 for each crystalline portion. It should be noted, however, that the number of amino acid residues of R12 is 54. 
     The sum of Gly and Ala in each of the crystalline portions (R01 to R11) exceeds ca. 70%. 
     Noncrystalline Portions: A01, A02, . . . , A11 
     They are composed of 28 to 32 amino acid residues and are called noncrystalline portion (A). 
     Their amino acid sequences are as follows: 
                                 A01   Gly Ser Ser Gly Phe Gly Pro Tyr Val Ala Asn Gly Gly Tyr Ser   (SEQ ID NO. 10)                               5                   10                  15                   Arg Ser Asp Gly Tyr Glu Tyr Ala Trp Ser Ser Asp Phe Gly Thr                           20                  25                  30               A02   Gly Ser Ser Gly Phe Gly Pro Tyr Val Ala His Gly Gly Tyr Ser   (SEQ ID NO. 11)                           5                   10                  15                   Gly Tyr Glu Tyr Ala Trp Ser Ser Glu Ser Asp Phe Gly Thr                           20                  25               A03   Gly Ser Ser Gly Phe Gly Pro Tyr Val Ala Asn Gly Gly Tyr Ser   (SEQ ID NO. 12)                           5                   10                  15                   Gly Tyr Glu Tyr Ala Trp Ser Ser Glu Ser Asp Phe Gly Thr                           20                  25               A04   Gly Ser Ser Gly Phe Gly Pro Tyr Val Ala His Gly Gly Tyr Ser   (SEQ ID NO. 13)                           5                   10                  15                   Gly Tyr Glu Tyr Ala Trp Ser Ser Glu Ser Asp Phe Gly Thr                           20                  25               A05   Gly Ser Ser Gly Phe Gly Pro Tyr Val Ala His Gly Gly Tyr Ser   (SEQ ID NO. 14)                           5                   10                  15                   Gly Tyr Glu Tyr Ala Trp Ser Ser Glu Ser Asp Phe Gly Thr                           20                  25               A06   Gly Ser Ser Gly Phe Gly Pro Tyr Val Ala Asn Gly Gly Tyr Ser   (SEQ ID NO. 15)                           5                   10                  15                   Gly Tyr Glu Tyr Ala Trp Ser Ser Glu Ser Asp Phe Gly Thr                           20                  25               A07   Gly Ser Ser Gly Phe Gly Pro Tyr Val Ala Asn Gly Gly Tyr Ser   (SEQ ID NO. 16)                           5                   10                  15                   Gly Tyr Glu Tyr Ala Trp Ser Ser Glu Ser Asp Phe Gly Thr                           20                  25               A08   Gly Ser Ser Gly Phe Gly Pro Tyr Val Ala Asn Gly Gly Tyr Ser   (SEQ ID NO. 17)                           5                   10                  15                   Gly Tyr Glu Tyr Ala Trp Ser Ser Glu Ser Asp Phe Gly Thr                           20                  25               A09   Gly Ser Ser Gly Phe Gly Pro Tyr Val Asn Gly Gly Tyr Ser   (SEQ ID NO. 19)                           5                   10                   Gly Tyr Glu Tyr Ala Trp Ser Ser Glu Ser Asp Phe Gly Thr           15                  20                  25               A10   Gly Ser Ser Gly Phe Gly Pro Tyr Val Ala Asn Gly Gly Tyr Ser   (SEQ ID NO. 19)                           5                   10                  15                   Gly Tyr Glu Tyr Ala Trp Ser Ser Glu Ser Asp Phe Gly Thr                           20                  25               A11   Gly Ser Ser Gly Phe Gly Pro Tyr Val Ala Asn Gly Gly   (SEQ ID NO. 20)                           5                   10                   Tyr Ser Arg Arg Glu Gly Tyr Glu Tyr Ala Trp Ser Ser               15                  20                  25                   Lys Ser Asp Phe Glu Thr                       30            
C-Terminal Portion: a
 
     The amino acid sequence of the noncrystalline portion on the C-terminal side is as follows: 
     
       
         
               
               
               
             
           
               
                 Ala Ala Ser Ser Val Ser Ser Ala Ser Ser Arg Ser Tyr Asp Tyr 
                 (SEQ ID NO. 21) 
                   
               
               
                                 5                   10                  15 
               
               
                   
               
               
                 Ser Arg Arg Asn Val Arg Lys Asn Cys Gly Ile Pro Arg Arg Gln 
               
               
                                 20                  25                  30 
               
               
                   
               
               
                 Leu Val Val Lys Phe Arg Ala Leu Pro Cys Val Asn Cys 
               
               
                                 35                  40 
               
             
          
         
       
     
     For convenience and reference to understand the present invention, notation for amino acids or amino acid residues in protein, charge characteristics thereof and the like are described in the following Table 10. 
     
       
         
               
               
               
               
             
           
               
                   
                 TABLE 10 
               
               
                   
                   
               
               
                   
                 1 character 
                 3 character 
                 Amino acid 
               
               
                   
                   
               
             
             
               
                   
                 A 
                 Ala 
                 alanine residues 
               
               
                   
                 C 
                 Cys 
                 cystine 
               
               
                   
                 D 
                 Asp 
                 aspartic acid 
               
               
                   
                 E 
                 Glu 
                 glutamic acid 
               
               
                   
                 F 
                 Phe 
                 phenylalanine 
               
               
                   
                 G 
                 Gly 
                 glycine 
               
               
                   
                 H 
                 His 
                 histidine 
               
               
                   
                 I 
                 Ile 
                 isoleucine 
               
               
                   
                 K 
                 lys 
                 lysine 
               
               
                   
                 L 
                 Leu 
                 leucine 
               
               
                   
                 M 
                 Met 
                 methionine 
               
               
                   
                 N 
                 Asn 
                 asparagine 
               
               
                   
                 P 
                 Pro 
                 proline 
               
               
                   
                 Q 
                 Gln 
                 glutamine 
               
               
                   
                 R 
                 Arg 
                 arginine 
               
               
                   
                 S 
                 Ser 
                 serine 
               
               
                   
                 T 
                 Thr 
                 threonine 
               
               
                   
                 V 
                 Val 
                 valine 
               
               
                   
                 W 
                 Trp 
                 tryptophan 
               
               
                   
                 Y 
                 Tyr 
                 tyrosine 
               
               
                   
                   
               
             
          
         
       
     
     Based on the side chain characteristics, amino acids are classified as four groups consisting of acidic amino acid, polar non-charged amino acid, non-polar amino acid and basic amino acid
     (1) Acidic amino acid: Glu, Asp   (2) Polar non-charged amino acid: Asn, Ser, Gln, Tyr, Thr, Cys, Phe   (3) Non-polar amino acid: Ala, Gly, Val, Pro, Leu, Ile, Trp   (4) Basic amino acid: His, Lys, Arg   

     The fibroin L-chain shown below is a noncrystalline portion, when compared to the amino acid sequences of the crystalline portions and the noncrystalline portions of the fibroin H-chain. 
     &lt;Amino Acid Sequence in Fibroin L-Chain&gt; 
     
       
         
               
               
               
             
           
               
                 Met Lys Pro Ile Phe Leu Val Leu Leu Val Ala Thr Ser Ala 
                 (SEQ ID NO. 22) 
                   
               
               
                                 5                   10 
               
               
                   
               
               
                 Tyr Ala Ala Pro Ser Val Thr Ile Asn Gln Tyr Ser Asp Asn 
               
               
                 15                  20                  25 
               
               
                   
               
               
                 Glu Ile Pro Arg Asp Ile Asp Asp Gly Lys Ala Ser Ser Val 
               
               
                     30                  35                  40 
               
               
                   
               
               
                 Ile Ser Arg Ala Trp Asp Tyr Val Asp Asp Thr Asp Lys Ser 
               
               
                         45                  50                  55 
               
               
                   
               
               
                 Ile Ala Ile Leu Asn Val Gln Glu Ile Leu Lys Asp Met Ala 
               
               
                             60                  65                  70 
               
               
                   
               
               
                 Ser Gln Gly Asp Tyr Ala Ser Gln Ala Ser Ser Val Ala Gln 
               
               
                                 75                  80 
               
               
                   
               
               
                 Thr Ala Gly Ile Ile Ala His Leu Ser Ala Gly Ile Pro Gly 
               
               
                 85                  90                  95 
               
               
                   
               
               
                 Asp Ala Cys Ala Ala Ala Asn Val Ile Asn Ser Tyr Thr Asp 
               
               
                     100                 105                 110 
               
               
                   
               
               
                 Gly Val Arg Ser Gly Asn Phe Ala Gly Phe Arg Gln Ser Leu 
               
               
                         115                 120                 125 
               
               
                   
               
               
                 Gly Pro Phe Phe Gly His Val Gly Gln Asn Leu Asn Leu Ile 
               
               
                             130                 135                 140 
               
               
                   
               
               
                 Asn Gln Leu Val Ile Asn Pro Gly Gln Leu Arg Tyr Ser Val 
               
               
                                 145                 150 
               
               
                   
               
               
                 Gly Pro Ala Leu Gly Cys Ala Gly Gly Gly Arg Ile Tyr Asp 
               
               
                 155                 160                 165 
               
               
                   
               
               
                 Phe Glu Ala Ala Trp Asp Ala Ile Leu Ala Ser Ser Asp Ser 
               
               
                     170                 175                 180 
               
               
                   
               
               
                 Ser Phe Leu Asn Glu Glu Tyr Cys Ile Val Lys Arg Leu Tyr 
               
               
                         185                 190                 195 
               
               
                   
               
               
                 Asn Ser Arg Asn Ser Gln Ser Asn Asn Ile Ala Ala Tyr Ile 
               
               
                             200                 205                 210 
               
               
                   
               
               
                 Thr Ala His Leu Leu Pro Pro Val Ala Gln Val Phe His Gln 
               
               
                                 215                 220 
               
               
                   
               
               
                 Ser Ala Gly Ser Ile Thr Asp Leu Leu Arg Gly Val Gly Asn 
               
               
                 225                 230                 235 
               
               
                   
               
               
                 Gly Asn Asp Ala Thr Gly Leu Val Ala Asn Ala Gln Arg Tyr 
               
               
                     240                 245                 250 
               
               
                   
               
               
                 Ile Ala Gln Ala Ala Ser Gln Val His Val 
               
               
                         255                 260 
               
             
          
         
       
     
     On the other hand, the amino acid sequence of silk protein from the wild silkworm is different from that of the domesticated silkworm, while wild silkworms belonging to the genus  Antheraea  such as  Antheraea yamamai, Antheraea pernyi, Samia cynthia ricini, Antheraea assama  and  Antheraea mylitta  have almost identical amino acid sequences. 
     For fibroin of  Antheraea yamamai , the portion consisting of a repetition of 10 or more alanine residues (A) alone is referred to crystalline portion, and the other portions besides this are referred to noncrystalline portion. 
     Compared to fibroin from the domesticated silkworm, fibroin from the wild silkworm belonging to the genus  Antheraea  has a smaller number of residues in each repetitive part of the crystalline portion and the noncrystalline portion. 
     The amino acid sequences of the noncrystalline portions of fibroin from  Antheraea yamamai  excepting the crystalline portions having 10 or more sequential alanine residues are shown below. 
     From the amino acid compositions, the N-terminal portion and the C-terminal portion are also noncrystalline portions. 
     &lt;Primary Structure of Noncrystalline Portions of Fibroin from  Antheraea yamamai &gt; 
     
       
         
               
               
               
             
           
               
                 N-terminal portion: initial peptide 
                 (SEQ ID NO. 23) 
                   
               
               
                 Met Arg Val Thr Ala Phe Val Ile Leu Cys Cys Ala Leu Gln 
               
               
                                 5                   10 
               
               
                   
               
               
                 Tyr Ala Thr Ala Asn Asn Leu His His His Asp Glu Tyr Val 
               
               
                 15                  20                  25 
               
               
                   
               
               
                 Asp Asn His Gly Gln Leu Val Glu Arg Phe Thr Thr Arg Lys 
               
               
                     30                  35                  40 
               
               
                   
               
               
                 His Tyr Glu Arg Asn Ala Ala Thr Arg Pro His Leu Ser Gly 
               
               
                         45                  50                  55 
               
               
                   
               
               
                 Asn Glu Arg Leu Val Glu Thr Ile Val Leu Glu Glu Asp Pro 
               
               
                             60                  65                  70 
               
               
                   
               
               
                 Tyr Gly His Glu Asp Ile Tyr Glu Glu Asp Val Val Ile Asn 
               
               
                                 75                  80 
               
               
                   
               
               
                 Arg Val Pro Gly Ala Ser Ser Ser Ala Ala Ala Ala Ser Ser 
               
               
                 85                  90                  95 
               
               
                   
               
               
                 Ala Ser Ala Gly Ser Gly Gln Thr Ile Ile Val Glu Arg Gln 
               
               
                     100                 105                 110 
               
               
                   
               
               
                 Ala Ser His Gly Ala Gly Gly Ala 
               
               
                         115                 120 
               
               
                   
               
               
                 Noncrystalline portions: 
               
               
                 Ala Gly Ala Ala Ala Gly Ala Ala Ala Gly Ser Ser Ala Arg 
                 (SEQ ID NO. 24) 
               
               
                                 5                   10 
               
               
                   
               
               
                 Gly Gly 
               
               
                 15 
               
               
                   
               
               
                 Ser Gly Phe Tyr Glu Thr His Asp Ser Tyr Ser Ser Tyr Gly 
                 (SEQ ID NO. 25) 
               
               
                                 5                   10 
               
               
                   
               
               
                 Ser Gly Ser Ser Ser Ala Ala Ala Ala Ser Ser Gly Ala Gly 
               
               
                 15                  20                  25 
               
               
                   
               
               
                 Gly Ala Gly Gly Gly Tyr Gly Trp Gly Asp Gly Gly Tyr Gly 
               
               
                     30                  35                  40 
               
               
                   
               
               
                 Ser Asp Ser 
               
               
                         45 
               
               
                   
               
               
                 Gly Ser Gly Ala Gly Gly Arg Gly Asp Gly Gly Tyr Gly Ser 
                 (SEQ ID NO. 26) 
               
               
                                 5                   10 
               
               
                   
               
               
                 Gly Ser Ser 
               
               
                 15 
               
               
                   
               
               
                 Arg Arg Ala Gly His Asp His Ala Ala Gly Ser Ser Gly Gly 
                 (SEQ ID NO. 27) 
               
               
                                 5                   10 
               
               
                   
               
               
                 Gly Tyr Ser Trp Asp Tyr Ser Ser Tyr Gly Ser Glu Ser 
               
               
                 15                  20                  25 
               
               
                   
               
               
                 Gly Ser Gly Ala Gly Gly Val Gly Gly Gly Tyr Gly Gly Gly 
                 (SEQ ID NO. 28) 
               
               
                                 5                   10 
               
               
                   
               
               
                 Asp Gly Gly Tyr Gly Ser Gly Ser Ser 
               
               
                 15                  20 
               
               
                   
               
               
                 Arg Arg Ala Gly His Asp Arg Ala Ala Gly Ser 
                 (SEQ ID NO. 29) 
               
               
                                 5                   10 
               
               
                   
               
               
                 Ser Gly Ala Gly Gly Ser Gly Gly Gly Tyr Gly Trp Gly Asp 
                 (SEQ ID NO. 30) 
               
               
                                 5                   10 
               
               
                   
               
               
                 Gly Gly Tyr Gly Ser Asp Ser 
               
               
                 15                  20 
               
               
                   
               
               
                 Gly Ser Gly Ala Gly Arg Ala Gly 
                 (SEQ ID NO. 31) 
               
               
                                 5 
               
               
                   
               
               
                 Gly Asp Tyr Gly Trp Gly Asp Gly Gly Tyr Gly Ser Asp Ser 
                 (SEQ ID NO. 32) 
               
               
                                 5                   10 
               
               
                   
               
               
                 Arg Gln Ala Gly His Glu Arg Ala Ala Gly Ser 
                 (SEQ ID NO. 33) 
               
               
                                 5                   10 
               
               
                   
               
               
                 Ser Gly Ala Gly Gly Ser Gly Arg Gly Tyr Gly Trp Gly Asp 
                 (SEQ ID NO. 34) 
               
               
                                 5                   10 
               
               
                   
               
               
                 Gly Gly Tyr Gly Ser Asp Ser 
               
               
                 15                  20 
               
               
                   
               
               
                 Gly Ser Gly Ala Gly Gly Ala Gly Gly Asp Tyr Gly Trp Gly 
                 (SEQ ID NO. 35) 
               
               
                                 5                   10 
               
               
                   
               
               
                 Asp Gly Gly Tyr Gly Ser Asp 
               
               
                 15                  20 
               
               
                   
               
               
                 Gly Ser Gly Ala Gly Gly Ala Gly Gly Asp Tyr Gly Trp Gly 
                 (SEQ ID NO. 36) 
               
               
                                 5                   10 
               
               
                   
               
               
                 Asp Gly Gly Tyr Gly Ser Asp Ser 
               
               
                 15                  20 
               
               
                   
               
               
                 Ser Gly Ala Gly Gly Ala Gly Gly Gly Tyr Gly Trp Gly Asp 
                 (SEQ ID NO. 37) 
               
               
                                 5                   10 
               
               
                   
               
               
                 Gly Gly Tyr Gly Ser Asp Ser 
               
               
                 15                  20 
               
               
                   
               
               
                 Ser Gly Ala Gly Gly Ala Gly Gly Tyr Gly Gly Tyr Gly Ser 
                 (SEQ ID NO. 38) 
               
               
                                 5                   10 
               
               
                   
               
               
                 Asp Ser 
               
               
                 15 
               
               
                   
               
               
                 Ser Gly Ala Gly Gly Ser Gly Gly Gly Tyr Gly Trp Gly Asp 
                 (SEQ ID NO. 39) 
               
               
                                 5                   10 
               
               
                   
               
               
                 Gly Gly Tyr Gly Ser Gly Ser 
               
               
                 15                  20 
               
               
                   
               
               
                 Gly Ser Gly Ala Gly Gly Val Gly Gly Gly Tyr Gly Trp Gly 
                 (SEQ ID NO. 40) 
               
               
                                 5                   10 
               
               
                   
               
               
                 Asp Gly Gly Tyr Gly Ser Asp Ser 
               
               
                 15                  20 
               
               
                   
               
               
                 Ser Gly Ala Gly Gly Arg Gly Asp Gly Gly Tyr Gly Ser Gly 
                 (SEQ ID NO. 41) 
               
               
                                 5                   10 
               
               
                   
               
               
                 Ser Ser 
               
               
                 15 
               
               
                   
               
               
                 Gly Ser Gly Ala Gly Gly Ala Gly Gly Gly Tyr Gly Trp Gly 
                 (SEQ ID NO. 42) 
               
               
                                 5                   10 
               
               
                   
               
               
                 Asp Gly Gly Tyr Gly Ser Asp Ser 
               
               
                 15                  20 
               
               
                   
               
               
                 Arg Arg Ala Gly His Asp Arg Ala Ala Gly Cys 
                 (SEQ ID NO. 43) 
               
               
                                 5                   10 
               
               
                   
               
               
                 Ser Gly Ala Gly Gly Thr Gly Gly Gly Tyr Gly Trp Gly Asp 
                 (SEQ ID NO. 44) 
               
               
                                 5                   10 
               
               
                   
               
               
                 Gly Gly Tyr Gly Ser Asp Ser 
               
               
                 15                  20 
               
               
                   
               
               
                 Ser Gly Ala Gly Gly Ser Gly Gly Gly Tyr Gly Trp Gly Asp 
                 (SEQ ID NO. 45) 
               
               
                                 5                   10 
               
               
                   
               
               
                 Gly Gly Tyr Gly Ser Asn Ser 
               
               
                 15                  20 
               
               
                   
               
               
                 Ser Gly Ala Gly Arg Ser Gly Gly Gly Tyr Gly Trp Gly Asp 
                 (SEQ ID NO. 46) 
               
               
                                 5                   10 
               
               
                   
               
               
                 Gly Gly Tyr Ser Ser Asp Ser 
               
               
                 15                  20 
               
               
                   
               
               
                 Ser Gly Ala Gly Gly Ser Gly Gly Tyr Gly Gly Tyr Gly Ser 
                 (SEQ ID NO. 47) 
               
               
                                 5                   10 
               
               
                   
               
               
                 Asp Ser 
               
               
                 15 
               
               
                   
               
               
                 Gly Ser Gly Ala Gly Gly Val Gly Gly Gly Tyr Gly Trp Gly 
                 (SEQ ID NO. 48) 
               
               
                                 5                   10 
               
               
                   
               
               
                 Asp Gly Gly Tyr Gly Gly Tyr Gly Ser Asp Ser 
               
               
                 15                  20                  25 
               
               
                   
               
               
                 Gly Ser Gly Ala Gly Gly Val Gly Gly Gly Tyr Gly Arg Gly 
                 (SEQ ID NO. 49) 
               
               
                                 5                   10 
               
               
                   
               
               
                 Asp Ser Gly Tyr Gly Ser Gly Ser Ser 
               
               
                 15                  20 
               
               
                   
               
               
                 Gly His Gly Arg Ser Ser Gly Ser 
                 (SEQ ID NO. 50) 
               
               
                                 5 
               
               
                   
               
               
                 Ser Gly Ala Gly Gly Ser Gly Gly Gly Tyr Gly Trp Asp Tyr 
                 (SEQ ID NO. 51) 
               
               
                                 5                   10 
               
               
                   
               
               
                 Gly Ser Tyr Gly Ser Asp Ser 
               
               
                 15                  20 
               
               
                   
               
               
                 Ser Ser Gly Ala Gly Gly Ser Gly Gly Gly Tyr Gly Trp Asp 
                 (SEQ ID NO. 52) 
               
               
                                 5                   10 
               
               
                   
               
               
                 Tyr Gly Gly Tyr Gly Ser Asp Ser 
               
               
                 15                  20 
               
               
                   
               
               
                 Gly Ser Gly Ala Gly Gly Ser Gly Gly Gly Tyr Gly Trp Gly 
                 (SEQ ID NO. 53) 
               
               
                                 5                   10 
               
               
                   
               
               
                 Asp Gly Gly Tyr Gly Ser Asp Ser 
               
               
                 15                  20 
               
               
                   
               
               
                 Ser Arg Arg Ala Gly His Asp Arg Ala Tyr Gly Ala Gly Ser 
                 (SEQ ID NO. 54) 
               
               
                                 5                   10 
               
               
                   
               
               
                 Gly Ala Gly Ala Ser Arg Pro Val Gly Ile Tyr Gly Thr Asp 
                 (SEQ ID NO. 55) 
               
               
                                 5                   10 
               
               
                   
               
               
                 Asp Gly Phe Val Leu Asp Gly Gly Tyr Asp Ser Glu Gly Ser 
               
               
                 15                  20                  25 
               
               
                   
               
               
                 C-terminal portion: 
               
               
                 Ser Ser Ser Gly Arg Ser Thr Glu Gly His Pro Leu Leu Ser 
                 (SEQ ID NO. 56) 
               
               
                                 5                   10 
               
               
                   
               
               
                 Ile Cys Cys Arg Pro Cys Ser His Arg His Ser Tyr Glu Ala 
               
               
                 15                  20                  25 
               
               
                   
               
               
                 Ser Arg Ile Ser Val His 
               
               
                     30 
               
             
          
         
       
     
     As to silk protein components excellent in promoting cell growth, an analysis was performed on which portion of each component is responsible for cell growth promotion in the present invention, disclosing that it was associated with the noncrystalline portions. 
     The noncrystalline portions of fibroin mean the portions having the amino acid sequences described above. 
     Accordingly, the N-terminal portion and the C-terminal portion are contained in the noncrystalline portions. 
     All of A01 to A11 (peptides of 28 to 32 residues) of the noncrystalline portions from the domesticated silkworm show similar excellent cell growth promotion, while the amino acid sequences of A01 to A11 are not identical. 
     The sequence of amino acid residues of A11 differs from that of each of other A01 to A10 within 8 residues out of its 32 residues. 
     Accordingly, even if there is ca. 30% or less difference in the sequence of amino acid residues, the cell growth-promoting activity is not influenced. 
     Even if there is an increase/decrease in the number of amino acid residues within ca. 20%, the cell growth promoting-activity is not influenced. 
     However, it is preferred that the difference in the amino acid sequences is less than 50% to retain the cell growth-promoting activity. 
     On the other hand, peptides having a very small number of amino acid residues may not express the cell growth-promoting activity. 
     Particularly when the number of amino acid residues is not more than two, the cell growth may be inhibited. 
     Therefore, peptides for the cell growth promotion are better to be peptides of from 4 to 40 residues, preferably from 6 to 32 residues. 
     Further, it was found that a partial peptide containing more acidic amino acid residues and/or polar non-charged amino acid residues and few basic amino acid residues in the noncrystalline portions is better for the cell growth promotion. 
     Particularly, acidic amino acid residues showed an excellent cell-growth promoting activity. 
     The noncrystalline portions show an excellent growth-promoting activity as a whole, whereas there exist, as a part, some sequence portions of amino acids showing a low growth-promoting activity because the sum of Gly and Ala exceeds 55% and also abundant basic amino acids are contained. 
     Accordingly, partial peptides in which acidic amino acids and/or polar non-charged amino acids are present and basic amino acids are hardly present and are separated and recovered from the noncrystalline portions of fibroin. 
     Among the recovered partial peptides, the peptides having 40 or less amino acid residues and showing a value of cell growth rate two fold higher than that of a control in which there is no added peptide in the cell culture test described in Examples 1 to 3 are designated as SDFGP. 
     A mixture of a plurality of peptides having 4 to 40 amino acid residues is also designated as SDFGP, as long as its cell growth rate shows 2-fold or higher activity than that of the control. 
     For the above conditions, a partial peptide from the noncrystalline portions is required to fulfill the following items, which is readily inferred from the results shown in Table 6:
     (1) The sum of the numbers of Gly and Ala relative to the total number of amino acid residues in a peptide is not higher than 55%. This is because a higher content of Gly and Ala is liable to form a crystal.   (2) The number of basic amino acid residues relative to the total number of amino acid residues in a peptide is not more than 25%.   (3) There exist acidic amino acids and/or polar non-charged amino acids.   

     When these conditions are not met, the cell growth may be inhibited. 
     In this connection, the properties of amino acids or peptides differ by the chemical structures of their side chains. 
     Although acidic amino acids are excellent for cell growth promotion, the length of the side chain differs between Glu and Asp, and thus, flexibility or conformation of the side chain and principal chain differs between them, thus contributing to dissimilar cell growth promotion. 
     Likewise, this is true for various amino acids referred to as polar non-charged amino acids or basic amino acids, and due to variations in physicochemical properties, the same cell promoting and cell inhibiting activities are not always exerted. 
     Cells forming our body are largely divided into adherent cells and floating cells. 
     The adherent cells include skin cells, vascular cells, gland cells, and the like. The floating cells include blood cells and the like. 
     The growth process of adherent cells starts with adhesion and then proliferation, and thus may be roughly divided into adhesion and proliferation. 
     SDFGP of the present invention has a property of supporting both adherence and proliferation, and is relatively better for adherence when compared between them. 
     Being better for proliferation gives rise to abnormal proliferation of cells, and may be associated with a safety issue for prolonged use. 
     Accordingly, SDFGP of the present invention which is good for adherence, has proliferation promotion, and does not inhibit cell growth is excellent for skin care materials and biomaterials. 
     When partial peptides are separated and recovered from silk protein in practice, silk protein is cleaved with a protease that cleaves specific peptide bonds or otherwise with a chemical serving the same purpose, and then, peptides that are formed of not more than 40 amino acid residues and belong to the noncrystalline portions are recovered. 
     In addition, it is also possible to design a peptide excellent for cell growth on the basis of the obtained peptides and then synthesize the peptide. 
     1. Separation and Recovery of Peptides from Silk Protein 
     In order to separate and recover the noncrystalline portions of silk protein, a characteristic of the noncrystalline portions may be used. 
     Since the noncrystalline portions are readily soluble in water, a silk material may be immersed in near neutral water (pH 5.0 to 9.0). 
     However, peptides of the noncrystalline portions cannot be efficiently obtained merely by the immersion of the silk material. 
     Hence, specific peptide bonds of silk protein are actively cleaved. 
     Such a cleavage method of peptide bonds preferably employs a chemical substance, an enzyme or the like which actively cleaves specific peptide bonds. 
     This is described below. 
     1) Raw Material 
     For the domesticated silkworm, raw material used is silk protein with fibroin H-chain, L-chain and remaining sericin a component. 
     For the wild silkworm (e.g.,  Antheraea yamamai, Antheraea pernyi, Samia cynthia ricini, Antheraea assama  and  Antheraea mylitta , and the like), raw material used is the one in which a band of the fibroin is observed on an electrophoretogram as clearly as that of the fibroin H-chain from the domesticated silkworm. 
     The raw material may be individually fibroin and sericin, or those existing together. 
     Thus, the raw material for the present invention may include all of cocoon filaments, raw silk, silk fabrics and knits, silk threads (fibroin fiber), remaining threads thereof or fibers, powder, film and the like with the use thereof as a raw material, and protein fiber material (silk material) spun by silkworm species such as domesticated silkworm and wild silkworm. 
     It should be noted that these materials have to contain the fibroin H-chain and sericin a component of domesticated silkworm and their corresponding components of wild silkworm. 
     Since the fibroin H-chain is more vulnerable to degradation than its L-chain, a partially remaining H-chain indicates that the L-chain is mostly left undegraded. 
     2) Solubilization of the Material 
     The material of the above 1) to be solubilized by a neutral salt may be a degummed material, half-degummed material, undegummed material, or an intermediate material thereof. 
     It may be sericin fiber from silkworm cocoon. 
     An important point is that their silk protein is not degraded or the fibroin H-chain, the a component of sericin and their corresponding proteins remain partially undegraded after various processing steps. 
     Whether the H-chain, the a component and the like remain or not is confirmed by the presence of their respective corresponding bands on an electrophoretogram. 
     The neutral salt to be used as a solubilizer for raw silk threads includes, for example, calcium chloride, copper ethylenediamine, sodium thiocyanate, lithium thiocyanate, lithium bromide, magnesium nitrate, and the like. 
     The neutral salt is preferably in an aqueous saturated solution or at a concentration not less than 50% saturation [weight (g)/volume (ml)]. 
     In the case where fibroin and sericin are contained, for example, cocoon filaments, undegummed material, half-degummed material, and the like are solubilized using the above neutral salt in a manner similar to that for silk threads. 
     On the other hand, when sericin occupies 98% or more, as in the case of sericin fiber from silkworm cocoon, the solubilization is carried out with 8 M urea within 10 min at 70 to 90 degrees C. 
     Moreover, sericin fiber from silkworm cocoon may be solubilized with 9 M LiBr within 30 min at room temperature (20 to 30 degrees C.). 
     The conditions for solubilization may be varied according to the above conditions. 
     At the step of solubilizing the silk material in a neutral salt solution, an alcohol such as methyl alcohol, ethyl alcohol and propyl alcohol may be added to the neutral salt. 
     When calcium chloride is used as the neutral salt, the solubilization is carried out at a temperature not higher than 94 degrees C., preferably in the range of from 75 to 85 degrees C. 
     When lithium bromide is used, the raw material is solubilized at a temperature lower than ca. 50 degrees C. Thus, depending on the neutral salt used, the conditions for solubilization vary, and a method in which the fibroin H-chain and the a component of sericin may remain or its corresponding method is employed for solubilization. 
     During solubilizing silk material,
     (1) the solubilization may be accelerated by stirring.   (2) the solubilization is difficult at a lower temperature.   

     Although a higher temperature may facilitate the solubilization, a vigorous lowering in molecular weight may take place. 
     The solution in which silk is solubilized with a neutral salt contains the neutral salt, alcohol, and so on besides fibroin or a mixture of fibroin and sericin. 
     From this solution, insoluble materials are first removed, and then low molecular weight compounds having a molecular weight lower than 5,000 are removed using a dialysis membrane or a dialysis equipment. 
     A solution of silk protein is obtained by such dialysis. 
     3) Degradation by Enzyme and Recovery 
     In general, it is said that cleavage of protein with a protease takes place at specific peptide bonds, and that modifications of the side chains of amino acid residues tend not to occur since its cleavage is carried out under a mild condition. 
     Furthermore, complicated fragmentation arising from nonspecific cleavage of protein may be avoided. 
     Such enzymes include lysyl endopeptidase, arginyl endopeptidase, chymotrypsin, papain, pepsin, rennin, pancreatin, elastase and the like. 
     When a protease is added to an aqueous solution of silk protein, the silk protein is cleaved between specific peptide bonds. 
     Among these, chymotrypsin is particularly preferred to separate the crystalline and noncrystalline portions. 
     When the cleaved peptides from silk protein are mainly composed of fragments generated from the crystalline portions of silk protein, these are prone to aggregate, and precipitate upon aggregation (coagulation or crystallization). 
     Even if their aggregation hardly occurs, peptides originating from the crystalline portion tend to aggregate more readily, and the addition of alcohol (methyl alcohol, ethyl alcohol, etc.) and the like as a coagulant triggers aggregation beginning from the peptides derived from the crystalline portions, and they precipitate out. 
     After removal of the precipitate, the remainder is a solution of peptides from the noncrystalline portions. 
     For the removal of the precipitate, the solution containing the precipitate is centrifuged (1,000 to 10,000 G) to remove it. 
     The solution freed of the precipitate is an aqueous solution of peptides, originating from the noncrystalline portions, which have been split off from the noncrystalline portions. 
     Upon drying this solution, film-like or powder-like peptides are obtained. 
     It should be noted that, when alcohol is added to the aqueous solution of peptides generated from the noncrystalline portions, the peptides from the noncrystalline portions start to aggregate in turn and precipitate out as the alcohol concentration becomes higher. 
     The peptides from the noncrystalline portions may contain partial peptides from the crystalline portions as long as the latter are within ca. 50%. 
     However, to obtain peptides excellent for promoting cell growth, the sum of glycine and alanine residues are preferred not to exceed 55%, even if the peptides are those from the noncrystalline portions. 
     Further, the number of basic amino acid residues is preferred not to be higher than 25% of that of the residues constituting the peptide. 
     On the other hand, larger numbers of acidic amino acid residues and non-polar charged amino acid residues are preferred. 
     Particularly, a larger number of acidic amino acid residues is better for cell growth promotion. 
     The drying is carried out by lyophilization or spray drying. 
     Even if the peptides from the noncrystalline portions are crystallized after drying, they are readily soluble in water owing to their lower molecular weights. 
     2. Synthesis of Fibroblast Growth-Promoting Peptide (SDFGP) from Silk Protein 
     The SDFGP separated and recovered from silk protein includes the following peptides: 
     These are merely examples of SDFGP. 
     Further, it goes without saying that there are many SDFGP satisfying the conditions described above. 
     
       
         
               
               
               
               
             
           
               
                 A-6-2 
                 Val Ile Thr Thr Asp Ser Asp Gly Asn Glu 
                 (SEQ ID NO. 1) 
                   
               
               
                   
                                 5                   10 
               
               
                   
               
               
                 A-6-6 
                 Asn Ile Asn Asp Phe Asp Glu Asp 
                 (SEQ ID NO. 2) 
               
               
                   
                                 5 
               
               
                   
               
               
                 SfHe 
                 Ala Ala Ser Ser Val Ser Ser Ala Ser Ser 
                 (SEQ ID NO. 3) 
               
               
                   
                                 5                   10 
               
               
                   
               
               
                   
                 Arg Ser Tyr Asp Tyr Ser Arg Arg Asn Val 
               
               
                   
                                 15                  20 
               
               
                   
               
               
                   
                 Arg Lys Asn 
               
               
                   
               
               
                 SfHA 
                 Gly Ser Ser Gly Phe Gly Pro Tyr Val Ala 
                 (SEQ ID NO. 4) 
               
               
                   
                                 5                   10 
               
               
                   
               
               
                   
                 His Gly Gly Tyr Ser Gly Tyr Glu Tyr Ala 
               
               
                   
                                 15                  20 
               
               
                   
               
               
                   
                 Trp Ser Ser Glu Ser Asp Phe Gly Thr 
               
               
                   
                                 25 
               
               
                   
               
               
                 AfH1 
                 Tyr Gly Trp Gly Asp Gly Gly Tyr Gly Ser 
                 (SEQ ID NO. 5) 
               
               
                   
                                 5                   10 
               
               
                   
               
               
                   
                 Asp Ser 
               
               
                   
               
               
                 AfH5 
                 Asp Glu Tyr Val Asp Asn 
                 (SEQ ID NO. 6) 
               
               
                   
                                 5 
               
               
                   
               
               
                 AfH6 
                 Val Glu Thr Ile Val Leu Glu Glu Asp Pro 
                 (SEQ ID NO. 7) 
               
               
                   
                                 5                   10 
               
               
                   
               
               
                   
                 Tyr Gly His Glu Asp Ile Tyr Glu Glu Asp 
               
               
                   
                                 15                  20 
               
               
                   
               
               
                 AfH7 
                 Asp Asp Gly Phe Val Leu Asp Gly Gly Tyr 
                 (SEQ ID NO. 8) 
               
               
                   
                                 5                   10 
               
               
                   
               
               
                   
                 Asp Ser Glu 
               
             
          
         
       
     
     Even only a portion of the amino acid sequences of these SDFGP may serve as SDFGP showing excellent cell-growth promotion. 
     Further, these peptides may be repeated within 40 residues or connected to other peptides. 
     However, a single amino acid state is not endowed with the cell growth-promoting function. 
     The number of amino acid residues required for cell growth-promoting function is not less than 4 residues. 
     On the other hand, its preferred number is 40 or less in view of the efficiency of peptide synthesis. 
     The synthesis of SDFGP mimics the amino acid sequences of the noncrystalline portions of silk protein, and the peptides which satisfy the conditions described above are synthesized. 
     The number of amino acid residues of a synthetic peptide is from 4 to 40, preferably from 6 to 32. 
     In this case, its amino acid sequence is not necessarily the same as that of silk protein. 
     For example, the amino acid sequences of the noncrystalline portions (A0 to A11) of the fibroin H-chain are not totally identical, while their growth promoting-activities are approximately the same, and all of them conform to SDFGP. 
     Accordingly, its amino acid sequence may differ about 30% or less, preferably differ 50% or less. 
     In this case, a larger number of acidic amino acids is better, and the presence of polar non-charged amino acids is preferred. 
     In contrast, the absence of basic amino acids is preferred. 
     In other words, the amino acid residues in each SDFGP may be replaced with other amino acid residues. 
     In this case, the number of basic amino acid residues is designed so as to become 25% or less of that constituting the peptide. 
     On the other hand, a larger number of acidic amino acids in a peptide (SDFGP) is preferred. 
     The whole amino acid residues may be composed of acidic amino acids and/or polar non-charged amino acids. 
     Thus, Asp Ser Asp Gly Asp Glu (SEQ ID NO. 70) from A-6-2, Asp Glu Asp Glu Asp Glu (SEQ ID NO. 71) and Glu Asp Glu Asp Glu Asp (SEQ ID NO. 72) from A-6-6, Ser Ser Glu Ser Ser Glu (SEQ ID NO. 73) and Tyr Gly Gly Tyr Glu Tyr (SEQ ID NO. 74) from SfHA, Asp Gly Gly Tyr Gly Gly Asp (SEQ ID NO. 75) from AfH 1, Asp Glu Tyr Asp Glu Tyr (SEQ ID NO. 76) from AfHS, Tyr Glu Glu Asp Tyr Glu Glu Asp (SEQ ID NO. 77) from AfHG, and the like, and further many more peptides such as Glu Glu Glu Glu (SEQ ID NO. 78), Glu Glu Glu Glu Glu Glu (SEQ ID NO. 79), Glu Tyr Glu Tyr Glu Tyr (SEQ ID NO. 80), Glu Glu Tyr Glu Glu Tyr (SEQ ID NO. 81), Tyr Tyr Tyr Tyr Tyr Tyr (SEQ ID NO. 82), Glu Gly Ser Glu Gly Ser (SEQ ID NO. 83) may become SDFGP. 
     It goes without saying that these peptides may be repeated or connected to other peptides as long as they are in the range of the conditions described above and have a molecular weight of 10,000 or less, preferably in the range of 4,000 to 400. In addition, the amino residues may be replaced with other amino acid residues. 
     4. Use 
     The peptide sets obtained from the noncrystalline portions of silk protein and SDFGP are not only excellent for cell growth promotion but also easily water-soluble. 
     Further, their molecular weights are approximately lower than 4,000, and therefore their forms are stable in a dissolved state for a prolonged period. 
     Still further, mixing various SDFGP may promote higher cell growth compared to a single SDFGP. 
     Therefore, a mixture of these is added to cell culture medium, lotion, milky lotion, cream, ointment, instillation, food, and the like. 
     Since the peptide sets and SDFGP of the present invention are excellent for promoting skin cell growth, they are excellent materials for skin care, cell culture, and further for improvements in other fields besides the above, for example, clothing fibers, cosmetic powders, resins, etc. 
     EXAMPLE 1 
     Cell Growth Activity of Enzymic Digests of Silk Fibroin 
     (1) Enzymic Degradation of the Noncrystalline Portions of Silk Fibroin, and Subsequent Separation and Fractionation 
     Cocoons of a domesticated silkworm were cut open to remove pupae, and cocoon layers (10 g) were immersed in 30 volumes of 8 M urea for 10 min at 90 degrees C. to extract sericin. 
     The residue after the extraction was washed with water, dried, and prepared as fibroin. 
     One g of fibroin was immersed in 10 ml of 9 M LiSCN to solubilize. To this, 10 ml of distilled water was added and centrifuged for 10 min at 3,000 rpm. 
     The supernatant was put into a semipermeable membrane tube and dialyzed against 50 volumes of water. 
     The dialysis was performed four times, changing the external dialysis water every 30 minutes. 
     After the dialysis, the solution was again centrifuged, and then 0.1 M sodium dihydrogenphosphate (pH 8.5) was added to adjust its pH to 7 to 8. 
     When chymotrypsin amounting to 1/100 of fibroin was added to that solution and left for 4 hours at 40 degrees C., precipitates were formed. 
     Proteins or peptides in the supernatant originating from the noncrystalline portion (A) of fibroin were designated as noncrystalline portion (A′), and proteins or peptides in the precipitates originating from the crystalline portion (C) were designated as crystalline portion (C′). 
     The crystalline portion was washed with water, dissolved in 1 ml of 9 M LiSCN and dialyzed against 50 volumes of water using a semipermeable membrane tube as described above, and the amount of protein in the aqueous solution was determined. 
     The amount of protein in the supernatant was determined without any further treatment. 
     (2) Coating on Cell Culture Vessel 
     The concentrations of aqueous solutions of these crystalline portion (C′) and noncrystalline portion (A′) were each adjusted to 0.025% and 0.0025%, respectively, by adding 70% ethanol, and 1 ml each of the diluted solutions was put into dishes (35 mmφ, Falcon) made of polystyrene and then air-dried. 
     Only 1 ml of 70% ethanol was added to dishes for control. 
     (3) Cell Culture 
     The cells used were human skin fibroblasts (originating from adult normal skin) purchased (frozen) from Sanko Junyaku Co., Ltd. 
     The culture medium used was the low serum culture medium for human skin fibroblast growth purchased from Kurabo Industries Ltd. (10 ml of LSGS (low serum growth supplement) added to 500 ml of Medium 106S (basal medium for skin fibroblast)). 
     It should be noted that LSGS has a cell growth-promoting activity. 
     The medium was added at 2 ml per dish, and 80,000 cells were inoculated and cultured for 3 days. 
     (4) Measurement of Viable Cell Number with Alamer Blue Dye 
     The medium at 2 ml per dish and Alamer Blue (Iwaki Glass Co.) at 0.1 ml per dish were added and cultured for 2 hours at 37 degrees C., and then the reduced amount of Alamer Blue dye calculated from the absorbances at 570 nm and 600 nm was correlated with viable cell number. 
     The growth of human skin fibroblasts in dishes coated with the crystalline portion and the noncrystalline portion compared to that of control (100%) having no silk protein component is shown in Table 1. 
     The cell growth rates in dishes coated with the silk protein components showed higher values in all cases compared to the control. 
     Particularly, the growth rate of the noncrystalline portion (C′) at 0.025% concentration was high. This portion is a mixture of SDFGP. 
     The growth rate of the crystalline portion at a higher concentration (0.025%) was worse than that at a lower concentration (0.0025%). 
     This is considered to be due to an inhibition of the cell growth by silk protein of the crystalline portion. 
     EXAMPLE 2 
     Amino Acid Sequence of Cell Growth-Promoting Peptides 
     It was found in Example 1 that the noncrystalline portion of fibroin promoted the cell growth more actively than the crystalline portion thereof. 
     However, the noncrystalline portion fractionated in Example 1 is likely to be a mixture of peptides generated by the enzymic cleavage. 
     Hence, the noncrystalline portion was further separated to identify the site of cell growth promotion. 
     First, reverse phase chromatography was carried out to separate the peptides contained in the noncrystalline portion in Example 1 according to their differences in polarity. 
     The column used was RESOURCER RPCk 3 ml. 
     The chromatography was conducted with 0.1% TFA (trifluoroacetic acid) in pump A and 0.1% TFA/90% acetonitrile in pump B at a gradient of from 0% of B to 75% of B within 0 min to 15 min. 
     As the result, 6 peaks (A-1, . . . , A-6) were confirmed. 
     Each peak was collected, dried with an evaporator, and redissolved in a small volume of buffer (PBS). 
     The concentrations of A-1 to A-6 were adjusted to 0.025% with 70% ethanol, respectively, and then 1 ml each was put in cell culture dishes (35 mmφ, Falcon) made of polystyrene and air-dried. 
     Control dishes contained only 70% ethanol at 1 ml, followed by air-drying. 
     Using these dishes, a cell culture experiment was conducted. 
     The method for cell culture was the same as that in Example 1. 
     The growth rates of human skin fibroblasts in dishes coated with the peptide fragments from the noncrystalline portion are shown in Table 2. 
     Among the fragments from the noncrystalline portion, A-6 was excellent for growth, showing ca. 4-fold enhancement compared to the control. 
     Next, separation of peptides contained in A-6, which showed the best cell growth-promoting activity, according to their molecular weights was performed on Superdex peptide HR10/30 (gel filtration chromatography). 
     As the result, 7 peaks, A-6-1 to A-6-7, were confirmed. 
     All were under 2,500 in their molecular weights. 
     Among the 7 peaks, peptides in sharp and distinct 5 peaks (A-6-2, A-6-3, A-6-4, A-6-6, A-6-7) were recovered, and each peptide was coated on cell culture dishes, whereinto the medium and cells were inoculated and cultured for 2 days, followed by the measurement of the cell growth. 
     The experiment for the cell growth was the same as that in Example 1. 
     The measurement results of cell growth rates are shown in Table 3. 
     The growth rates of A-6-2 and A-6-6 after 2-day culture were 1.5 fold higher than the growth of the control, showing excellent cell growth promotion. 
     The growth rates after 3-day culture exceeded 2 fold. 
     Subsequently, the amino acid sequences of A-6-2 and A-6-6 were analyzed on LF3000 Protein Sequencer of BI Technologies Japan Ltd., and their amino acid sequences were found to be as follows: 
     
       
         
               
               
               
               
             
           
               
                 A-6-2 
                 Val Ile Thr Thr Asp Ser Asp Gly Asn Glu 
                 (SEQ ID NO. 1) 
                   
               
               
                   
                                 5                   10 
               
               
                   
               
               
                 A-6-6 
                 Asn Ile Asn Asp Phe Asp Glu Asp 
                 (SEQ ID NO. 2) 
               
               
                   
                                 5 
               
             
          
         
       
     
     Both A-6-2 and A-6-6 were peptides from the N-terminal side of fibroin. 
     The N-terminal portion is a noncrystalline portion based on the amino acid composition. 
     Next, the peptides of A-6-2 and A-6-6 were synthesized (contracted out to Hokkaido System Science Co., Ltd.), and physiological activities of the synthesized peptides were determined after a 3-day culture as described above, confirming that these showed cell growth promotion as the extracts from silk protein did. 
     In addition, when the synthesized A-6-2 and A-6-6 peptides were mixed, its cell growth promotion was superior to that of each peptide present individually in the cell culture. 
     EXAMPLE 3 
     Cell Growth Rates of Synthetic Peptides 
     Synthetic peptides (contracted out to Hokkaido System Science Co., Ltd.), which were derived from a total of 12 sites based on the amino acid sequences of the fibroin H-chain of the domesticated silkworm and the fibroin of  Antheraea yamamai , were measured for their cell activity. 
     (1) Peptide Synthesis 
     Partial peptides from 2 sites of the crystalline portions (SfHC-1, SfHC-2), and partial peptides from 2 sites of the noncrystalline portions (SfHE, SfHA) were picked up from the fibroin of the domesticated silkworm and synthesized. 
     Further, Ala-repeating site (AfH0) of the crystalline portion and 7 partial peptides (AfH1 to AfH7) of the noncrystalline portions were picked up from the fibroin of  Antheraea yamamai  and synthesized. 
     The partial peptides from the fibroin H-chain of the domesticated silkworm were 4 kinds, and the partial peptides from the fibroin of  Antheraea yamamai  were 8 kinds (AfH0 to AfH7). Each amino acid sequence of these peptides is shown below. 
     Partial Peptides from Fibroin H-Chain of Domesticated Silkworm (4 Kinds) 
                                 SfHC-1   Gly Ala Gly Ala Gly Ser Gly Ala Gly Ala   (SEQ ID NO. 57)                               5                   10                   Gly Ser Gly Ala Gly Ala Gly Tyr Gly Ala                           15                  20                   Gly Tyr               SfHC-2   Gly Ala Gly Ala Gly Ser Gly Ala Ala Ser   (SEQ ID NO. 58)                           5                   10                   Gly Ala Gly Ala Gly Ala Gly Ala Gly Ala                           15                  20                   Gly Thr               SfHE   Ala Ala Ser Ser Val Ser Ser Ala Ser Ser   (SEQ ID NO. 59)                           5                   10                   Arg Ser Tyr Asp Tyr Ser Arg Arg Asn Val                           15                  20                   Arg Lys Asn               SfHA   Gly Ser Ser Gly Phe Gly Pro Tyr Val Ala   (SEQ ID NO. 60)                           5                   10                   His Gly Gly Tyr Ser Gly Tyr Glu Tyr Ala                           15                  20                   Trp Ser Ser Glu Ser Asp Phe Gly Thr                           25            
Partial Peptides from Fibroin of  Antheraea yamamai  (Eight Kinds)
 
                                 AfH 0   Ala Ala Ala Ala Ala Ala Ala Ala Ala Ala   (SEQ ID NO. 61)                               5                   10               AfH 1   Tyr Gly Trp Gly Asp Gly Gly Tyr Gly Ser   (SEQ ID NO. 62)                           5                   10                   Asp Ser               AfH 2   Ser Gly Ala Gly Gly Ser Gly Gly Tyr Gly   (SEQ ID NO. 63)                           5                   10                   Gly Tyr Gly Ser Asp Ser                           15               AfH 3   Gly Ser Gly Ala Gly Gly Arg Gly Asp Gly   (SEQ ID NO. 64)                           5                   10                   Gly Tyr Gly Ser Gly Ser Ser                           15               AfH 4   Arg Arg Ala Gly His Asp Arg Ala Ala Gly   (SEQ ID NO. 65)                           5                   10                   Ser               AfH 5   Asp Glu Tyr Val Asp Asn   (SEQ ID NO. 66)                           5               AfH 6   Val Glu Thr Ile Val Leu Glu Glu Asp Pro   (SEQ ID NO. 67)                           5                   10                   Tyr Gly His Glu Asp Ile Tyr Glu Glu Asp                           15                  20               AfH 7   Asp Asp Gly Phe Val Leu Asp Gly Gly Tyr   (SEQ ID NO. 68)                           5                   10                   Asp Ser Glu            
(2) Coating of Synthetic Peptides on Dishes
 
     About 1 mg each of the synthetic peptides was dissolved in 200 μl of PBS. The dissolved peptide solutions were diluted with 70% ethanol to adjust to 0.025% and 0.0025% concentrations, and 1 ml each of these solutions were put in dishes and dried. 
     SfHC-1, SfHC-2 and SfHE were difficult to dissolve, and therefore, 1 ml of 9 M LiSCN was added to dissolve them. 
     The dissolved solutions were put into semipermeable membrane tubes and dialyzed against 100 volumes of water with changes of external water every 30 minutes, and then their protein amounts were confirmed by an absorbance at 275 nm. 
     SfHC-2 is free of tyrosine and the like, and therefore its absorbance measurement was not possible. Since SfHC-1 and SfHE were present approximately in the same amount as they were present before dissolution, SfHC-2 was presumed to be present in the same amount as well and diluted with 70% ethanol in the same way as that used for other peptides, put in dishes and dried. 
     Further, AfH0 was also hard to dissolve and seemed to be lost upon dialysis due to its small molecular weight, and therefore it was dissolved by stirring well after dilution with. 70% ethanol, put in a dish and dried. 
     (3) Cell Culture 
     The cells used were human skin fibroblasts (originating from adult normal skin) purchased (frozen) from Sanko Junyaku Co. Ltd. 
     The culture medium used was the low serum culture medium for human skin fibroblast growth purchased from Kurabo Industries Ltd. 
     The medium was added at 2 ml per dish, and ca. 80,000 cells were inoculated and cultured for 3 days. 
     Then, 0.1 ml of Alamer Blue (Iwaki Glass Co.) was added and cultured for 2 hours at 37 degrees C., and the reduced amount of Alamer Blue calculated from the absorbances at 570 nm and 600 nm was correlated with viable cell number. 
     The method of these measurements for cell culture is the same as that in Example 1. 
     The results are shown in Tables 4 and 5. 
     As to the fibroin from the domesticated silkworm, the partial peptides of the noncrystalline portions, SfHE and SfHA, were higher in the growth rate compared to those of the partial peptides of the crystalline portions, SfHC-1 and SfHC-2, and showed more than 2-fold higher values than the control value, indicating that the partial peptides of the noncrystalline portions or their mixtures are SDFGP. 
     There was little activity in AfH0 which is a partial peptide of the crystalline portion of the fibroin from  Antheraea yamamai , and the higher concentration (0.025%) was lower in the growth rate, suggesting an inhibition of the cell growth. 
     The synthetic partial peptides of the noncrystalline portion, AfH1 to AfH7, showed cell growth promotion with differences in their growth rates. 
     For example, both of AfH3 and AfH6 contain one basic amino acid residue, respectively. Since AfH3 contains less acidic amino acid residues and AfH6 contains more acidic amino acid residues, AfH6 showed higher cell growth promotion. 
     Particularly, AfH1, AfH5, AfH6 and AfH7 showed excellent cell growth promotion, and all of these are SDFGP obtained by synthesis. 
     As shown in Table 5, not all partial peptides derived from the noncrystalline portions become SDFGP with high growth rates. 
     As shown in Table 6, this is due to the differences in the chemical structures of side chains of the amino acids constituting each peptide. 
     EXAMPLE 4 
     Cell Growth Activity of Synthetic Peptides 
     Based on the results in Examples 1 to 3, synthetic peptides (contracted out to Hokkaido System Science Co., Ltd.) having acidic amino acids and polar non-charged amino acids, which were supposed to show a cell growth activity, as the main components were measured for their fibroblast growth-promoting activity. 
     The measurements for the cell growth activity were carried out by a method similar to that in Example 1. 
     The cell culture was performed for 3 days, and the results obtained at a peptide concentration of 0.025 μg/cm 2  are shown in Table 7. 
     As to glutamic acid, four or more sequential residues were excellent for cell growth activity. 
     EXAMPLE 5 
     Promotion of Cell Adhesion and Proliferation by Synthetic Peptides 
     The cell growth activities of synthetic peptides originating from silk protein, synthetic peptides having mainly acidic amino acids or polar non-charged amino acids, or the like were further measured in detail by dividing into cell adhesion and cell proliferation. 
     This method partly differs from the method in (3) Cell culture of Example 1. 
     In the present cell culture, the cells used were human skin fibroblasts (originating from adult normal skin) purchased (frozen) from Sanko Junyaku Co. Ltd. 
     The culture medium used was the low serum culture medium for human skin fibroblast growth purchased from Kurabo Industries Ltd. (Medium 106S 500 ml). 
     The medium 106S is a basal medium for skin fibroblasts. 
     LSGS (low serum growth supplement) was not used here. 
     In the measurement of adhesion, the cells floating in the medium at 5 hours after inoculation of cells into the medium were removed, and the viable cell number adhering to the bottom of a dish was measured. 
     In the measurement of proliferation, the viable cell number at 3 days after inoculation of cells into the medium was measured. 
     Besides the cell culture method, coating of peptides on cell culture dishes, measurement of viable cell number with Alamer Blue dye, and the like were carried out as described in Example 1. 
     The results obtained for adhesion and those obtained for proliferation are shown in Tables 8 and 9, respectively, in comparison with the viable cell number of the control (100%) where no peptide was coated on dishes. 
     Namely, Table 8 shows adhesion after culturing human skin fibroblasts for 5 hours in dishes coated with various peptides. 
     Here, the synthetic peptides are shown either by symbol or amino acid sequence. 
     In this case, the concentration of each peptide coated on dishes was 0.025 μg/cm 2 . 
     The adhesion rate (%) in the case where no peptide was coated was set at 100. 
     Table 9 shows the proliferation after 3-day culturing of human skin fibroblasts in dishes coated with various peptides. 
     Here, the synthetic peptides are shown either by symbol or amino acid sequence. 
     In this case, the concentration of each peptide coated on dishes was 0.025 μg/cm 2 . 
     The growth rate (%) in the case where no peptide was coated was set at 100. 
     It should be noted that the viable cell number in the control in 3-day culturing increased about 150% during the culture and the control value (100%) was based on the viable cell number after 3-day culture. 
     Accordingly, when there was no increase or decrease in the cell number after 3-day culturing, the growth rate would become about 70%. 
     
       
         
               
             
               
               
               
               
             
               
               
               
               
             
           
               
                 TABLE 1 
               
             
             
               
                   
               
               
                 Growth rates of human skin fibroblasts in dishes coated 
               
               
                 with crystalline portion and noncrystalline portion 
               
             
          
           
               
                   
                   
                   
                 Significant 
               
               
                   
                   
                   
                 difference from 
               
               
                   
                   
                 Growth rate 
                 control; Confidence 
               
               
                   
                 Concentration 
                 (%) 
                 rate (%) 
               
               
                   
                   
               
             
          
           
               
                 Control 
                   
                 100 ± 8.6* 
                   
               
               
                 Crystalline 
                  0.025% 
                 149 ± 5.6 
                 99.9 
               
               
                 portion (C′) 
                 0.0025% 
                 174 ± 8.8 
                 99.0 
               
               
                 Noncrystalline 
                  0.025% 
                 259 ± 10.3 
                 99.0 
               
               
                 portion (A′) 
                 0.0025% 
                 164 ± 5.0 
                 99.0 
               
               
                   
               
               
                 (*Standard deviation) 
               
             
          
         
       
     
     
       
         
               
             
               
               
               
             
               
               
               
             
           
               
                 TABLE 2 
               
             
             
               
                   
               
               
                 Growth of human skin fibroblasts in dishes coated with 
               
               
                 peptide fragments from noncrystalline portion 
               
             
          
           
               
                   
                   
                 Significant difference from 
               
               
                   
                 Growth rate (%) 
                 control; Confidence rate (%) 
               
               
                   
                   
               
             
          
           
               
                 Control 
                 100 ± 15.0* 
                   
               
               
                 A-1 
                 124 ± 6.0 
                 &lt;95 
               
               
                 A-2 
                 171 ± 3.5 
                 99 
               
               
                 A-3 
                 148 ± 4.5 
                 95 
               
               
                 A-4 
                 215 ± 12.0 
                 99 
               
               
                 A-5 
                 269 ± 13.0 
                 99.9 
               
               
                 A-6 
                 389 ± 12.2 
                 99.9 
               
               
                   
               
               
                 (*Standard deviation) 
               
             
          
         
       
     
     
       
         
               
             
               
               
               
             
               
               
               
             
           
               
                 TABLE 3 
               
             
             
               
                   
               
               
                 Growth rates of human skin fibroblasts in dishes coated 
               
               
                 with 5 fragments obtained from the peptide chain (Table 2, A-6) 
               
             
          
           
               
                   
                   
                 Significant difference from 
               
               
                   
                 Growth rate (%) 
                 control; Confidence rate (%) 
               
               
                   
                   
               
             
          
           
               
                 Control 
                 100 ± 6.1* 
                   
               
               
                 A-6-2 
                 153 ± 2.7 
                 99.9 
               
               
                 A-6-3 
                 139 ± 15.2 
                 98.0 
               
               
                 A-6-4 
                 105 ± 12.2 
                 &lt;95.0 
               
               
                 A-6-6 
                 159 ± 6.6 
                 99.0 
               
               
                 A-6-7 
                 124 ± 4.3 
                 99.0 
               
               
                   
               
               
                 (*Standard deviation) 
               
             
          
         
       
     
     
       
         
               
             
               
               
               
               
             
               
               
               
               
             
           
               
                 TABLE 4 
               
             
             
               
                   
               
               
                 Growth of human skin fibroblasts in dishes coated with 
               
               
                 synthetic partial peptides of fibroin of domesticated silkworm 
               
             
          
           
               
                   
                   
                   
                 Significant 
               
               
                   
                   
                   
                 difference from 
               
               
                   
                   
                 Growth rate 
                 control; Confidence 
               
               
                   
                 Concentration 
                 (%) 
                 rate (%) 
               
               
                   
                   
               
             
          
           
               
                 Control 
                   
                 100 ± 1.5* 
                   
               
               
                 SfHC-1 
                  0.025% 
                 194 ± 2.3 
                 99.9 
               
               
                   
                 0.0025% 
                 146 ± 6.0 
                 99.9 
               
               
                 SfHC-2 
                  0.025% 
                 136 ± 1.0 
                 99.9 
               
               
                   
                 0.0025% 
                 116 ± 8.9 
                 95 
               
               
                 SfHE 
                  0.025% 
                 243 ± 3.9 
                 99.9 
               
               
                   
                 0.0025% 
                 198 ± 12.5 
                 99 
               
               
                 SfHA 
                  0.025% 
                 316 ± 5.7 
                 99.9 
               
               
                   
                 0.0025% 
                 321 ± 6.2 
                 99.9 
               
               
                   
               
               
                 (*Standard deviation) 
               
             
          
         
       
     
     
       
         
               
             
               
               
               
               
             
               
               
               
               
             
           
               
                 TABLE 5 
               
             
             
               
                   
               
               
                 Growth of human skin fibroblasts in dishes coated with 
               
               
                 synthetic partial peptides of fibroin of  Antheraea yamamai   
               
             
          
           
               
                   
                   
                   
                 Significant 
               
               
                   
                   
                   
                 difference from 
               
               
                   
                   
                 Growth rate 
                 control; Confidence 
               
               
                   
                 Concentration 
                 (%) 
                 rate (%) 
               
               
                   
                   
               
             
          
           
               
                 Control 
                   
                 100 ± 26.5* 
                   
               
               
                 AfH0 
                  0.025% 
                 100 ± 7.4 
                 &lt;50 
               
               
                   
                 0.0025% 
                 152 ± 6.1 
                 95 
               
               
                 AfH1 
                  0.025% 
                 396 ± 4.0 
                 99 
               
               
                   
                 0.0025% 
                 179 ± 13.5 
                 98 
               
               
                 AfH2 
                  0.025% 
                 196 ± 9.4 
                 99 
               
               
                   
                 0.0025% 
                 118 ± 14.7 
                 60 
               
               
                 AfH3 
                  0.025% 
                 194 ± 24.5 
                 98 
               
               
                   
                 0.0025% 
                 111 ± 9.0 
                 &lt;50 
               
               
                 AfH4 
                  0.025% 
                 133 ± 8.7 
                 80 
               
               
                   
                 0.0025% 
                 113 ± 4.8 
                 50 
               
               
                 AfH5 
                  0.025% 
                 344 ± 7.7 
                 99.9 
               
               
                   
                 0.0025% 
                 192 ± 11.3 
                 99 
               
               
                 AfH6 
                  0.025% 
                 264 ± 9.0 
                 99.9 
               
               
                   
                 0.0025% 
                 152 ± 9.0 
                 95 
               
               
                 AfH7 
                  0.025% 
                 284 ± 25.1 
                 99.9 
               
               
                   
                 0.0025% 
                 155 ± 5.3 
                 95 
               
               
                   
               
               
                 (*Standard deviation) 
               
             
          
         
       
     
     
       
         
               
             
               
               
               
               
               
             
               
               
               
               
               
               
               
             
               
               
               
               
               
               
               
             
           
               
                 TABLE 6 
               
             
             
               
                   
               
               
                 Percentage of each amino acid group constituting 
               
               
                 synthetic peptides and cell growth rates 
               
               
                 (The cell growth rates in Tables 4 and 5 are values 
               
               
                 obtained at higher peptide concentration (0.025%)) 
               
             
          
           
               
                 Partial peptide 
                   
                 Number 
                   
                   
               
               
                 of fibroin of 
                   
                 of 
               
               
                 domesticated 
                 Cell 
                 residues 
                   
                 Basic amino 
               
               
                 silkworm and 
                 growth 
                 in 
                 Gly + Ala 
                 acids 
               
             
          
           
               
                 
                   Antheraea yamamai 
                 
                 rate (%) 
                 peptide 
                 Number 
                 (%) 
                 Number 
                 (%) 
               
               
                   
               
             
          
           
               
                 SfHC-1 
                 194 
                 22 
                 18 
                 82 
                 0 
                 0 
               
               
                 SfHC-2 
                 136 
                 22 
                 19 
                 86 
                 0 
                 0 
               
               
                 SfHE 
                 243 
                 23 
                 3 
                 13 
                 5 
                 4 
               
               
                 SfHA 
                 316 
                 29 
                 9 
                 31 
                 1 
                 13 
               
               
                 AfH0 
                 100 
                 10 
                 10 
                 100 
                 0 
                 0 
               
               
                 AfH1 
                 396 
                 12 
                 5 
                 50 
                 0 
                 0 
               
               
                 AfH2 
                 196 
                 16 
                 9 
                 56 
                 0 
                 0 
               
               
                 AfH3 
                 194 
                 17 
                 10 
                 59 
                 1 
                 6 
               
               
                 AfH4 
                 133 
                 11 
                 5 
                 46 
                 4 
                 36 
               
               
                 AfH5 
                 344 
                 6 
                 0 
                 17 
                 0 
                 0 
               
               
                 AfH6 
                 264 
                 20 
                 1 
                 35 
                 1 
                 5 
               
               
                 AfH7 
                 284 
                 13 
                 3 
                 46 
                 0 
                 0 
               
               
                   
               
             
          
         
       
     
     
       
         
               
             
               
               
             
               
               
               
             
           
               
                 TABLE 7 
               
             
             
               
                   
               
               
                 Cell growth activity of synthetic peptides 
               
             
          
           
               
                 Amino acid or amino acid 
                   
               
               
                 sequence of peptides 
                 Cell growth rate (%) 
               
               
                   
               
             
          
           
               
                 Glu 
                   
                 69 
               
               
                 Glu Glu 
                   
                 159 
               
               
                 Glu Glu Glu Glu 
                 (SEQ ID NO. 78) 
                 231 
               
               
                 Glu Glu Glu Glu Glu Glu 
                 (SEQ ID NO. 79) 
                 346 
               
               
                 Glu Glu Glu Glu Glu Glu 
                 (SEQ ID NO. 84) 
                 254 
               
               
                 Glu Glu Glu Glu 
               
               
                 Tyr Tyr 
                   
                 113 
               
               
                 Tyr Tyr Tyr Tyr 
                 (SEQ ID NO. 85) 
                 156 
               
               
                 Tyr Tyr Tyr Tyr Tyr Tyr 
                 (SEQ ID NO. 82) 
                 239 
               
               
                 Asp Glu Asp Glu Asp Glu 
                 (SEQ ID NO. 71) 
                 322 
               
               
                 Glu Tyr Glu Tyr Glu Tyr 
                 (SEQ ID NO. 80) 
                 207 
               
               
                 Glu Glu Tyr Glu Glu Tyr 
                 (SEQ ID NO. 81) 
                 212 
               
               
                   
               
             
          
         
       
     
     
       
         
               
             
               
               
               
             
               
               
               
             
           
               
                 TABLE 8 
               
             
             
               
                   
               
               
                 Adhesion after 5 hour-culture of human skin fibroblasts 
               
               
                 in dishes coated with each peptide 
               
             
          
           
               
                   
                 Synthetic peptide 
                 Adhesion rate (%) 
               
               
                   
                   
               
             
          
           
               
                   
                 SfHC-1 
                 130 
               
               
                   
                 SfHC-2 
                 138 
               
               
                   
                 SfHA 
                 205 
               
               
                   
                 SfHE 
                 190 
               
               
                   
                 AfH0 
                 131 
               
               
                   
                 AfH1 
                 169 
               
               
                   
                 AfH2 
                 149 
               
               
                   
                 AfH3 
                 174 
               
               
                   
                 AfH4 
                 151 
               
               
                   
                 AfH5 
                 234 
               
               
                   
                 AfH6 
                 135 
               
               
                   
                 AfH7 
                 153 
               
               
                   
                 Asp Glu Asp Glu Asp Glu (SEQ ID NO. 71) 
                 229 
               
               
                   
                   
               
             
          
         
       
     
     
       
         
               
             
               
               
               
             
               
               
               
             
           
               
                 TABLE 9 
               
             
             
               
                   
               
               
                 Growth after 3 day-culture of human skin fibroblasts in 
               
               
                 dishes coated with each peptide 
               
             
          
           
               
                   
                 Synthetic peptide 
                 Growth rate (%) 
               
               
                   
                   
               
             
          
           
               
                   
                 SfHC-1 
                 71 
               
               
                   
                 SfHC-2 
                 97 
               
               
                   
                 SfHA 
                 159 
               
               
                   
                 SfHE 
                 126 
               
               
                   
                 AfH0 
                 102 
               
               
                   
                 AfH1 
                 94 
               
               
                   
                 AfH2 
                 71 
               
               
                   
                 AfH3 
                 69 
               
               
                   
                 AfH4 
                 96 
               
               
                   
                 AfH5 
                 108 
               
               
                   
                 AfH6 
                 77 
               
               
                   
                 AfH7 
                 89