A novel arginine deiminase, its manufacturing method and an anti-cancer agent containing this enzyme as an effective ingredient

Abstract: A novel arginine deiminase of an approximately 45,000 molecular weight derived from mycoplasma having an ability to decompose arginine, and the method of manufacturing this novel enzyme from mycoplasma. This enzyme is an effective anti-cancer agent, as it shows anti-cancer activities both in vitro and in vivo.

Description: BACKGROUND OF THE INVENTION The present invention relates to a novel arginine deiminase and the manufacturing method thereof. Further, the present invention relates to an anti-cancer agent containing this arginine deiminase as an effective ingredient. DESCRIPTION OF THE RELATED ART Recently, increasing attention is focused on the fresh attempt to cure cancer by using enzymes on the basis of the requirement of nourishment by cancer cells. In other words, this treatment attempts to inhibit the growth of, or necrotize, the cancer cells by decomposing the nourishment required by the cancer cells and thus by shutting out the source of nourishment from the reach of the cancer cells. Among these anti-tumor enzymes, L-asparaginase (EC 3.5.1.1) [see Nature, 299 , 168(1971)] and arginase (EC 3.5.3.1) [Br. J. Cancer, 19 , 379(1965)] are known. However, L-asparaginase is effective only to a few types of cancer such as leukemia and malignant lymphoma because there are a small number of cancers dependent on L-asparagine, while arginase fails to show anti-cancer activities in vivo although it shows inhibiting activities against the growth of a variety of cancer cells in vitro [Br. J. Cancer, 30 , 50(1974)]. Moreover, although there have been reports that arginine deiminase is obtainable from mycoplasma and other microorganisms [J.Biol.chem., 241 , 2228-2236 (1966), ibid. , 252 , 2615-2620 (1987) , ibid., 250 , 4580-4583 (1975), Arch.Biochem.Biophys. 69 , 186-197 (1957), etc.], no reports have mentioned the anti-cancer activity of this enzyme. SUMMARY OF THE INVENTION It is an object of the present invention to provide a novel arginine deiminase. Another object is to provide a method of manufacturing this novel arginine deiminase from mycoplasma. Further, the other object of the present invention is to provide an anti-cancer agent containing arginine deiminase as an effective ingredient. The present inventors researched into many new types of arginine deiminase derivable from Pseudomonas, Streptococcus, mycoplasma and other microorganisms. As a result, the present invention was accomplished when it was found that a cell extract of mycoplasma contains arginine deiminase, which has its optimum pH in the physiological range, shows a high stability, and consequently provides strong inhibiting activities against the growth of cancer cells. Arginine deiminase (EC 3.5.3.6.) is an enzyme that hydrolyzes amidino group of L-arginine into L-citrulline and ammonia, and is called by a general name of arginine dihydrolase, arginine desiminase, or guanidinodesiminase. The resultant L-citrulline is decomposed into ornithine and carbamoyl phosphate, and this carbamoyl phosphate is further decomposed into ammonia and water. ATP is produced in this process. In other words, arginine deiminase is an enzyme involved in the first step of the pathway leading to the production of ATP in connection with the metabolism of the amidino groups of arginine in bacteria and yeasts. The arginine deiminase of the present invention is derived from mycoplasma and has the following physicochemical properties: (a) Function Hydrolyzes the amidino groups of L-arginine into L-citrulline and ammonia. (b) Optimum pH: 6.0 - 7.5 (c) Stable pH: 4.5 - 9.0 (d) Optimum temperature: Approx. 50°C (e) Km value: Approx. 0.2 mM (f) Isoelectric point (PI): Approx. 4.7 (g) Molecular weight: Approx. 45,000 (by SDS-polyacrylamide gel electrophoresis method) Approx. 90,000 (by gel filtration HPLC method) (h) Amino acid sequence from N-terminal Ser-Val-Phe-Asp-Ser-Lys-Phe-Lys-Gly-Ile -His-Val-Tyr-Ser-Glu- Also, the arginine deiminase of the present invention comprises the amino acid sequence shown in Fig. 4. The arginine deiminase of the present invention is prepared from mycoplasma by the following method: Any mycoplasma having an ability to produce the arginine deiminase of the present invention can be used. These types of mycoplasma include M.arginini, M. hominis, M. salivarium, M. gallinarum and M. orale. The most suitable strain is the M. arginini [IFO Catalog No. 14476, ATCC Catalog No. 23838 or NCTC Catalog No. 10129) available from the Institute of Fermentation, Osaka, ATCC or NCTC. In the present invention, the above mycoplasma is cultured in a liquid medium added with arginine, at a temperature of about 37°C for one to several days in a standing condition. This mycoplasma is a facultative anaerobic bacterium and can be grown under an anaerobic condition or in the presence of oxygen. A PPLO meat broth or the like is used, and arginine is added to the medium at a ratio of 1-10g to 1 liter of medium. After culturing, the cells are collected, then are suspended in a buffer solution, for example, such as a phosphate buffer solution, and are disrupted by such means as sonication; finally, the precipitates are removed through centrifugal separation or a similar method. The supernatant solution is thus obtained as a cell extraction, which undergoes a process of purification by chromatography such as gel filtration chromatography, ion-exchange chromatography, affinity chromatography and the like. As a result, an arginine deiminase having the above-mentioned physicochemical properties is obtained. The arginine deiminase of the present invention is clearly different from the known types of arginine deiminase reported in various literature, as shown in Table 1. Reference (Present invention) J.B.C. 252,2615-2620 (1987) J.B.C. 241,2228-2236 (1966) J.B.C. 250,4580-4583 (1975) Archives of Biochemistry and Biophysics 69, 186-197 (1957) Source M. arginini M.arthritidis M.hominis Pseudomonas putida Streptococcus faecalis Molecular weight 45,000 (SDS-PAGE) 9,000 (Gel filtration HPLC) 49,000 (SDS-PAGE) 78,300 54,000 (SDS-PAGE) not known Isoelectric point 4.7 7.0 not known 6.13 not known km 0.2mM 4 µM 0.1-0.4 mM 0.2mM 0.15mM Vmax 50u/mg 18u/mg 53u/mg 58.8u/mg 41u/mg Optimum pH 6.7-7.5 not known 6.5-6.7 6.0 6.8 Amino acid at N-terminal Ser Ala not known not known not known Further, the homology search was done between the N-amino acid sequence of the arginine deiminase of the present invention and registered proteins in the computer database, but it was found that no protein has an amino acid sequence similar to that obtained by the present invention. For these reasons, it has been concluded that the arginine deiminase of the present invention is a novel arginine deiminase. In addition, an attempt was made in the present invention to clone the gene of arginine deiminase of M.arginini from the genome DNA of M.arginini. By DNA sequence analysis of the cloned gene, a nucleotide sequence coding for the arginine deiminase was determined, as illustrated in Fig. 4. Accordingly, the arginine deiminase of the present invention was found to contain the 409 amino acids and have a molecular weight of 46375, nearly identical with the molecular weight of proteins obtained by the SDS-polyacrylamide gel electrophoresis. As indicated by Experiments 1 through 6, the arginine deiminase of the present invention shows a superb effect of prolonging the lives of mice carrying such cancer cells as leukemia cells, fibrosarcoma cells and colon carcinoma cells and the like. For this reason, it is evident that the arginine deiminase of the present invention is effective in the treatment of a variety of tumors, specially malignant tumors, in humans. The activity of arginine deiminase can be determined by causing it to produce citrulline using the method reported by Fenske et. al. [J. Bacteriol. 126 , 501-510 (1976)], and by measuring the amount of the yields using the method given by Archibald [J. Biol. Chem. 156 , 121-142 (1944)]. Specifically, 20 µl of arginine deiminase solution is added to 1.0ml of 10mM arginine [dissolved in 0.1M phosphate buffer of pH 7.0], then an enzyme reaction is allowed to take place at 37°C for 10 minutes, and the reaction is terminated by adding 1ml of mixed acid solution (H₂SO₄ : H₃PO₄ = 1 : 3). Then, the resultant reactive solution is added with 25 µl of 3% aqueous diacetylmonooxim solution, heated at 100°C for 20 minutes under a light-shielded condition, left to cool under a room temperature for 30 minutes, and then the amount of the citrulline yield is measured quantitatively by measuring the absorbence at 490nm. The activity of arginine deiminase producing 1 µmol of citrulline in one minute is defined as 1 unit. With regard to an acute toxicity of arginine deiminase, there was no case of mouse dead due to the administration of not more than 1 mg/mouse of arginine deiminase orally or intravenously in the tail. Further, the dissection of the administered animals showed no irregularities in their organs, thus affirming the high safety of arginine deiminase. The arginine deiminase of the present invention can be administered by injection (hypodermic injection, intravenous injection or arterial injection, etc.) in a variety of pharmaceutical preparation and formulations. It may be used by combinding with any other pharmaceutical active ingredient, carriers and/of adjuvants. A variety of preparation forms are permissible, such as suspension, fluid, emulsion, ampule and any other injection forms. The agent of the present invention can be prepared by any known means of pharmaceutical preparation. As the dosage of arginine deiminase of the present invention varies according to the individual variation, diesease conditions and the like, the arginine deiminase may be administered in an amount of 0.1-100mg/1Kg of human body weight per day. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 shows a gel filtration chromatogram of the M.arginini cell extract of the present invention, Fig. 2 an ion-exchange chromatogram of the fractions 42-52 thereof, and Fig. 3 affinity chromatogram of the fractions 50-53 thereof. Fig. 4 shows the complete amino acid sequence of the arginine deiminase, and the nucleotide sequence which codes for the enzyme. Fig. 5 through Fig. 8 show the nucleotaide sequence and amino acid sequence thereto of the oligonucleotide used as probes. DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS Examples of the present invention are shown below. Example 1 Preparation of arginine Deiminase (1) Culturing of M.arginini A strain of M.arginini (IFO Catalog No. 14476) obtained from the Institute of Fermentation, Osaka was inoculated into a liquid medium [composed of 21g of PPLO broth w/o CV (Difco), 10g of L-arginine, 200ml of horse serum, 100ml of 25% freshly prepared yeast extract, 5ml of 0.4% phenol red solution and 700ml of distilled water, and adjusted pH to 7.0], and then cultured in a 5% CO₂ incubator at 37°C for 2 days in a standing condition. (2) Separation and purification of arginine deiminase (A) Preparation of M.arginini cell extract 2g of M.arginini cells were separated by centrifuging 2 liters of the liquid medium obtained according to the above (1) step, at a 7,000 rpm for 20 minutes. These M.arginini cells were suspended in 30ml of 10mM phosphate buffer of pH 7.0. The cells contained in this suspension were then disrupted by sonication, and the insoluble matter is removed by centrifugal separation. Finally, the resultant supernatant was obtained as a M.arginini cell extract. (B) The purification of arginine deiminase Arginine deiminase MS purified from the M. arginini cell extract obtained in the above (A) step, by applying the following three different types of chromatography. i) Gel filtration chromatography The above M.arginini cell extract was applied to gel filtration chromatography under the following condition, using a Cellulofine GCL-2000m [Chisso Corporation]: Column size: 2.6 x 90cm Volume of gel : 480ml Flow rate: 24ml/hr Volume of fraction: 6 ml each Eluent: 10mM potassium phosphate buffer (pH 7.0), + 0.5M sodium chloride The absorbance at 280 nm and arginine deiminase activity of each fraction thus obtained were measured by the aforementioned methods, and the results were as shown in Fig. 1. It was found that the arginine deiminase was contained in the fractions 42- 52. ii) Ion-exchange chromatography The fractions 42-52 obtained in the above i) step were dialyzed for 24 hours against a 10mM phosphate buffer. Then, the inner dialyzed solution was applied to ion-exchange chromatography under the following condition, using a DEAE-Toyopearl [Toso Co.]: Column size: 2.6 x 30cm Volume of gel : 320ml Flow rate: 60ml/hr Volume of fraction: 10 ml each Eluent: 10mM phosphate buffer (pH 7.0) (linear gradient of sodium chloride from 0 to 0.5M) In other words, the dialyzed fractions containing the arginine deiminase were added into a DEAE-Toyopearl column equilibrated with the same buffer as that used in the dialysis in order to absorb arginine deiminase, and 10 ml of each fraction was collected by elution under the condition of a linear gradient of the sodium chloride concentration from 0M to 0.5M in the buffer at a flow rate of 60ml/hr. As in the above i) step, the absorbance at 280nm and arginine deiminase activity of each fraction were measured, and the results were as shown in Fig. 2. It was found that the arginine deiminase was contained in the fractions 50-53. iii) Affinity chromatography The fractions 50-53 obtained in the above ii) step were dialyzed for 24 hours against a 10mM potassium phosphate buffer . Then, the dialyzed solution was applied to affinity chromatography under the following condition, using a Arginine-Sepharose 4B [Pharmacia Co.]: Column size: 2.2 x 10cm Volume of gel : 38ml Flow rate: 50ml/hr Volume of fraction: 8ml each Eluent: 10mM phosphate buffer (pH 7.0) (linear, gradient of sodium chloride from 0 to 1.0M) In other words, the dialyzed fractions containing the arginine deiminase were added into a Arginine-Sepharose column equilibrated with the same buffer as that used in dialysis in order to absorb arginine delminase, and 8ml of each fraction was collected by elution under the condition of a linear gradient from 0M to 1.0M of the sodium chloride concentration In the buffer at a flow rate of 50ml/hr. As in the above ii) step, the absorbance at 280nm and arginine deiminase activity of each fraction were measured, and the results were as shown in Fig. 3. It was found that the arginine deiminase was contained in the fractions 71-81. iv) SDS-polyacrylamide gel electrophoresis The fractions 71-81 obtained in the above iii) step were analyzed by SDS-polyacrylamide gel electrophoresis according to the method reported by Laemmli et. al. [Nature, 727 , 680-685 (1970)]. The purification of arginine deiminase was confirmed, as a single band was observed at a molecular weight of 45,000. (C) Physicochemical properties of arginine deiminase The following measurements were made with the enzyme solution obtained in the above (B) iii) step: i) Optimum pH, optimum temperature, stable pH and stable temperature The optimum pH range is 6.0-7.5, and the stable pH range when treated at 4°C for 24 hours is 4.5-9.0. The highest activity is obtained in the 45-55°C temperature range, and as for stability against temperature, the activity is completely lost for treatment at 95°C for 5 minutes or at 60°C for 30 minutes. ii) Substrate specificity The arginine deiminase hydrolyzes L-arginine to produce L-citrulline and ammonia. iii) Molecular weight Measurement by the SDS-polyacrylamide gel electrophoresis indicated a molecular weight of approximately 45,000. Measurement by the gel filtration HPLC method using a TSK G3000SW XL [Toso Co.] indicated a molecular weight of approximately 90,000. iv) Isoelectric point Measurement of the isoelectric point by the electrofocusing method indicated an isoelectric point of approximately 4.7. v) Km value and Vmax value By the Lineweaver-Burk plot analysis Km and Vmax were determined as 0.2mM and 50U/mg, respectively. vi) The amino acid sequence from the N-terminal was determined by a peptide sequencer [Applied Biosystem Co.] as follows: Ser-Val-Phe-Asp-Ser-Lys-Phe-Lys-Gly-Ile -His-Val-Tyr-Ser-Glu- vii) Biological Activity The arginine deiminase showed an inhibiting activity against the growth of cancer cells in vitro, and indicated a superb effect of prolonging the lives of cancer-carrying mice in vivo. Example 2 (1) Preparation of mycoplasma genome DNA M.arginini [IFO Catalog No. 14476] was lysed by SDS, and then was treated first by protinase K and then by RNase A. Then, the solution was extracted with phenol and then with chloroform; finally, genome DNA was prepared by dialyzing the resultant aqueous layer against 10mM tris-hydrochloric acid (pH 8.0) in 1mM EDTA. (2) Preparation of mycoplasma genes library The mycoplasma genome DNA prepared in the above (1) step was digested by appropriate restriction enzymes, then was inserted to a plasmidvector pUC19 [Toyobo Co.]; finally, this vector was introduced into E. coli HB101 [purchased as competent cells from Takara Shuzo Co.], to provide a mycoplasma genes library. (3) Design and synthesis of oligonucleotide for hybridization probe It was previously reported that the DNA of mycoplasma contains only a small amount of GC [Proc. Natl. Acad. Sci., 84 , 166-169 (1987)]. In view of this finding, an oligonucleotide having 24 bases (a mixture of 4 types, and see Fig. 5 through 8 for their sequences) was designed from the N-terminal amino acid sequence of the arginine deimlnase, and was synthesized by a DNA synthesizer [ABI model 308 B]. (4) Screening by colony hybridization The oligonucleotide synthesized in the above (3) step was labeled by 32p, and was used as a probe for screening the mycoplasma gene library produced in the (2) step. Thus, positive clones were isolated. (5) Determination of nucleotide sequences Plasmid DNA was prepared from the clones obtained in the above (4) step, and the DNA fragment to be hybridized with the probe was integrated into M13mp19 [Toyobo Co.]. Using the dideoxy method, the nucleotide sequence was determined for both strands of the cloned gene. The results are shown in Fig. 4. A 1230 bp open reading frame including a nucleotide sequence coding for the N-terminal, 30 amino acids sequence of the arginine deiminase was found in the cloned gene, and the 1227 bp genes, following the initiation codon ATG, were identified as the arginine deiminase gene of M.arginini (see Fig. 4). Since it is known that the TGA codon is recognized as a tryptophan codon in mycoplasma [Proc. Natl. Acad. Sci., 82 , 2306-2309 (1985)], the TGA codons existing at 5 different positions in the arginine deiminase genes were considered as tryptophan codons, and the analysis was performed on the assumption that there were only 2 termination codons, TAA and TAG. The molecular weight derived from the total 409 amino acids was 46375, which is nearly identical with the molecular weight obtained by the protein SDS-polyacrylamide gel electrophoresis. Example 3 Preparation of formulated arginine deiminase The fractions 71-81 obtained in the Example 1 (2) iii) step were dialyzed for 24 hours against a phosphate buffered saline (PBS) (pH 7.4), and the dialyzed product was diluted by PBS in a 0.2-2.0mg/ml solution. Then, the solution was sterilized by filtration with a 0.2 µm filter, to prepare an aqueous solution-type arginine deiminase preparation. Example 4: Expression of Arginine Deiminase by Transformant (1) Production of Mutant Gene In accordance with the Kunkel method [Proc. Natl. Acad. Sci. USA, 82 , 488 (1985)], point mutation was carried out to replace all of the 5 TGA codons of the arginine deiminase gene (shown in Fig. 4) by TGG codons which are the tryptophan codons of E. coli, using 5 different types of oligonucleotide as primers. Then, clones in which all of the 5 TGA codons have been replaced by TGG codons were selected by the plaque hybridization method using the above oligonucleotide as a probe. The selected clones were sequenced to make sure that all of the 5 TGA codons had been replaced by TGG codons. (2) Preparation of Arginine Deiminase expressing Vector (pAD 12) Plasmid pAD 12 was prepared by inserting, into the Sac I-Hind III site of plasmid pVC 19, genes containing the structural genes and regulatory genes 240 bq upstream therefrom of the mutant arginine deiminase genes obtained in the above (1) step. The resultant plasmid pAD 12 was found to have a promoter sequence of mycoplasma arginini arginine deiminase, and an analysis of the base sequence of the pAD 12 indicated the presence of a consensus sequence (SD, - 10, -35 sequence) of the procaryotic cell promoter. Thus, it was considered possible that the plasmid pAD 12 serve as a vector expressing arginine deiminase of E. coli. (3) Culturing of Transformants and preparation of Cell Extract The pAD 12 prepared in the above (2) step was introduced to E. coli HB 101 (Takara Shuzo Co.), and the resultant transformant was cultured overnight at 37°C in a 5 ml LB medium [1.0% Bacto Tryptone (DIFCO Co.), 0.5% Bacto Yeast Extract (DIFCO Co.), 0.2% glucose, 1.0% NaCl, pH 7.5]. Then, 1 ml of the culture medium was added to 250 ml of LB medium to be cultured overnight at 37°C. The cell collected from the culture by centrifugation was washed twice with physiological saline, and were suspended in 2 ml of 0.1M potassium phosphate buffer (pH 7.0). Then, the cells were disruped by sonication, and the supernatant after the removal of insolubles by centrifugation was obtained as the cell extract. The same process was repeated to prepare a cell extract of E. coli HB 101 retaining the pUC 19 which did not contain arginine deiminase genes. This extract was used as the control. (4) Measurement of Arginine Deiminase Activity The HB 101 cell extract retaining pAD 12 and the HB 101 cell extract retaining pUC 19 (control) both obtained in the (3) step were diluted 10 times by a 0.1 M potassium phosphate buffer (pH 7.0), and 10 µl of each resultant solution was incubated at 37°C for 5 hours. Then, the amount of citrulline yield was measured by the aforementioned method. The amount of arginine deiminase expression in the HB 101 retaining pAD 12 was calculated from the difference between the amount of the citrulline yield in the HB 101 retaining pAD 12 and that in the HB 101 retaining pUC 19. The result indicated 1.2 unit of arginine deiminase activity for every 250 ml of LB medium. In addition, test results concerning the anti-cancer effects of the arginine deiminase of the present invention are presented in the experiments below. Experiment: Anti-cancer effects of arginine deiminase Experiment 1: Method Using Cultured Strains of Human Cancer Cells First, 1 x 10⁴ cells of each type of human cancer cells were inoculated in a 24-well microplate containing 1.0ml of DME medium with a 10% serum of bovine fetal serum, and the arginine deiminase preparation obtained in the above step was added to this medium, in such an amount that the concentration of this preparation in the medium was 5ng/ml or 10ng/ml. Then, after culturlng in a 5% CO₂ incubator at 37°C for 3 days, the number of cancer cells were counted using an automated cell counter (Coultor counter) [Coultor Co.]. As the control, the same amount of PBS was added to the medium instead of the arginine deiminase preparation. The inhibiting activity against cancer cell growth was indicated in terms of the number of cancer cells in samples, relative to the corresponding number for the control which was set as 100. The results are as shown in Table 2. Type of cell No. of cells (% of control) 5ng/ml 10ng/ml Human liver cancer cell (HLE) 16.7 6.7 Human malignant fibro-sarcoma cell (B32) 20.1 10.3 Human squamous carcinoma cancer cell (Caski) 31.6 22.9 Human squamous carcinoma cancer cell (HSC-4) 57.4 41.8 Human malignant melanoma cells (VMRC) 41.7 23.4 Human nasopharyngeal carcinoma cell (KB) 57.1 46.9 Human lung carcinoma cells (A549) 42.3 45.8 Experiment 2: Method Using Mouse Leukemia Cells L1210 A total of 21 male CDF₁ mice (BALB/c♀ x DBA/B♂), 7 weeks old, were used, as subjects, and 1 x 10⁵ cells of leukemia cells L1210 were transplanted i.p. to each mouse. Then, 9 mice were randomly selected as a control group, and the other were equally devided into 2 test groups. The aforementioned arginine deiminase preparations were chronically injected i.p. to the test groups daily for 8 days. The control group animals were administered with PBS. Experiment 3: Method Using Mouse Flbro-sarcoma Meth A A total of 27 male CDF₁ mice (BALB/c♀ x DBA/2♂), 7 weeks old, were used as subjects, and 1 x 10⁶ cells of fibro-sarcoma cells Meth A were transplanted i.p. to each mouse. Then, 9 mice were randomly selected as a control group, and the others were equally devided into 2 test groups. The arginine deiminase preparations were chronically injected i.p. to the test groups daily for 10 days. The control group animals were administered with PBS. Experiment 4: Method Using Mouse Colon carcinoma Cells Colon 26 A total of 25 male CDF₁ mice (BALB/c♀ DBA/2♂), 7 weeks old, were used as subjects, and 1 x 10⁶ cells of colon carcinoma cells Colon 26 were transplanted i.p. to each mouse. Then, 9 mice were randomly selected as a control group, and the others were equally devided into 2 test groups . The arginine deiminase preparations were chronically injected i.p. to the test groups daily for 14 days. The control group animals were administered with PBS. Experiment 5 : Method Using Mouse Sarcoma 180 A total of 24 male ICR mice, 7 weeks old, were used as subjects, and 1 x 10⁶ cells of Sarcoma 180 cells were transplanted i.p. to each mouse. Then, 8 mice were randomly selected as a control group, and the others were equally devided into 2 test groups. The arginine deiminase preparations were chronically injected i.p. daily for 14 days to the test groups. The control group animals were administered with PBS. Experiment 6 : Method Using Mouse Ascites Hepatoma MH 134 A total of 26 male C3H/HeN mice, 7 weeks old, were used as subjects, and 1 x 10⁶ cells of Ascites Hepatoma MH 134 were transplanted i.p. to each mouse. Then, 10 mice were randomly selected as a control group, and the others were equally devided into 2 groups. The arginine deiminase preparations were chronically injected i.p. daily for 14 days to the test groups. The control group animals were administered with PBS. The anti-cancer effect was indicated in terms of the percentage (T/C %) of the average number of days lived by the test groups in comparison with that by the control group. The results obtained from the above Experiments 2 through 6 are shown in Tables 3 through 7, respectively. (L1210) Group Ave. No. of days lived T/C(%) Control (N=9) 8.4±0.7 (100) 0.25mg/mouse (N=6) 9.3±0.5 111 0.5 mg/mouse (N=6) 10.3±1.4 126 (Meth A) Group Ave. No. of days lived T/C(%) Control (N=9) 10.6±1.6 (100) 0.1 mg/mouse (N=9) 10.7±0.7 101 0.5 mg/mouse (N=9) 12.6±1.7 118 (Colon 26) Group Ave. No. of days lived T/C(%) Control (N=9) 11.1±1.3 (100) 0.1 mg/mouse (N=8) 11.9±1.4 107 0.5 mg/mouse (N=8) 21.8±4.6 196 (Sarcoma 180) Group Ave. No. of days lived T/C(%) Control (N=8) 21.3 ± 9.9 (100) 0.04 mg/mouse (N=8) 35.3 ± 13.3 166 0.2 mg/mouse (N=8) 48.4 ± 9.0 228 ( MH 134 ) Group Ave. No. of days lived T/C(%) Control (N=10) 25.0 ± 6.7 100 0.04 mg/mouse (N=8) > 75 > 300 0.2 mg/mouse (N=8) > 75 > 300

Claims: A polypeptide derived from mycoplasma and characterized by an arginine deiminase activity and the following physicochemical properties: (a) Function and substrate specifity: Hydrolizes the amidino groups of L-arginine to L-citrulline and ammonia (b) Optimum pH: 6.0 to 7.5 (c) Stable pH: 4.5 to 9.0 (d) Optimum temperature: Approximately 50 °C (e) Km value: Approximately 0.2 mM (f) Isoelectric point (pI): Approximately 4.7 (g) Molecular weight: Approximately 45,000 by SDS-polyacrylamide gel electrophoresis; and approximately 90,000 by gel filtration HPLC (h) Amino acid sequence from N-terminal: Ser-Val-Phe-Asp-Ser-Lys-Phe-Lys-Gly-Ile-His-Val-Tyr-Ser-Glu-. A polypeptide derived from mycoplasma and characterized by the amino acid sequences shown in figure 4. A method of preparing a polypeptide according to claim 1 or 2 and characterized in that mycoplasma capable of decomposing arginine is cultured and that the cultured product is treated by a process of extraction, separation and purification to obtain the polypeptide. A method according to claim 3 of preparing a polypeptide as described in claim 2 wherein the mycoplasma capable of decomposing arginine is an M. arginini strain. A method according to claim 3 or 4, characterized in that oligonucleotides shown in figures 5 to 8 are used as probes for screening. A DNA comprising a nucleotide sequence which codes for the polypeptide according to claim 1 or 2. A method of preparing a polypeptide as described in claim 2 and characterized in that microorganisms transformed by a plasmid including a DNA described in claim 6 are cultured and that the cultured product is separated and purified to obtain the polypeptide. An anti-cancer agent containing as an effective ingredient a polypeptide according to claim 1 or 2.

Inventors: AOSHIMA MIHO C O NIPPON MINING, MIYAZAKI KAORU, TAKAKU HARUO C O NIPPON MINING, AOSHIMA, MIHO, C/O NIPPON MINING CO.,LTD., MIYAZAKI, KAORU, TAKAKU, HARUO, C/O NIPPON MINING CO.,LTD.
Applicants: JAPAN ENERGY CORP, JAPAN ENERGY CORPORATION
Application year: 1990
Main classification: C12N9
IPC codes: A61K38, A61P35, C12N15, C12R1, C12N9