bluuebunny/crossref_metadata_2025_split huggingface dataset:
STEREOCHEMICAL RESTRICTIONS ON THE OCCURRENCE OF AMINO ACID RESIDUES IN THE COLLAGEN STRUCTURE
Authors: Bansal M. 
Published: August 2010

The primary structure of collagen is characterized by the repeating tripeptide sequence (Gly‐R2‐R3)n. The results of theoretical studies, carried out using contact criteria to compute the stereochemically allowed orientations for various side chains at locations 2 and 3, are reported here. It is found that side chains with only γ‐atoms, as in valine, serine and threonine, or with only one δ‐methyl group, as in isoleucine, can occur equally well at locations 2 and 3, as is actually the case in collagen. Side chains with two Cδ‐atoms, as in leucine and phenyl‐alanine, can also be accommodated at both positions. However, if they occur as R3 their freedom of orientation is severely restricted in the presence of a proline residue as R2 in a neighbouring chain.If water molecules bound to the chains of the triple helix are assumed to be present, then location 3 is virtually impossible for leucine and phenylalanine residues. Location 2 is, however, unaffected, and their presence as R2 can help to shield the water molecules from disturbance by the solvent medium. This may be the reason for the preferential occurrence of Leu and Phe residues in location 2 in the collagen triplets, although the polypeptides (Gly‐Pro‐Leu)n and (Gly‐Pro‐Phe)n form collagen‐like structures.
SOME OBSERVATIONS ON THE CARBOHYDRATE COMPOSITION OF PURIFIED TRANSFERRIN
Authors: Wong K.‐L. , Regoeczi E. 
Published: August 2010

Five subfractions were isolated on DEAE‐cellulose from samples of a commercially available human transferrin preparation and their carbohydrate composition was analysed. Hexosamine, galactose and total hexose were determined in four subfractions and sialic acid in all five.The data obtained indicate that the excess number of electrophoretic bands observed in transferrin from this source is due to the loss of carbohydrates which only affects sialic acid and none of the other sugar types. The availability of the penultimate galactose residues as the terminal residues in the subfractions deficient in sialic acid was also confirmed by a biological test utilizing the rat liver.The reason for the gradual loss of sialic acid from transferrin is unknown. Freezing‐thawing and lyophilization did not detectably affect the sialic acid content of purified transferrin. However, free sialic acid did appear in some preparations on storage.It is concluded that similar changes in the carbohydrate composition of other plasma glycoproteins before, during, or after purification can be expected to exert an adverse effect on their usefulness as metabolic tracers.
FLUORESCENT LABELLING OF 6–PHOSPHOGLUCONATE DEHYDROGENASE FROMBACILLUS STEAROTHERMOPHILUS:
Authors: Fontana Angelo , Mantovanelli Ludovico , Boccu Enrico , Veronese Francesco M. 
Published: August 2010

The thermophilic 6–phosphogluconate dehydrogenase from Bacillus stearo‐thermophilus was inhibited upon specific modification of the ‐SH group of cysteine residues by 7–chloro‐4–nitrobenzo‐2–oxa‐1, 3–diazole (NBD‐Cl) at pH 7.0. By using 20–100–fold molar excess of NBD‐CL the reaction occurs slowly at pH 7.0 as a first order process. Partial protection from inactivation was observed when the substrate 6–phosphogluconate or the coenzyme NADP was added to the reaction mixture. Complete inactivation was achieved upon modification of 1.9 of the six cystine residues per mole of enzyme, which corresponds to nearly one residue per enzyme subunit.Circular dichroism measurements suggest that the gross structure of the protein molecule is practically unchanged upon reaction of the enzyme with NBD‐Cl. Melting profile experiments revealed a single transition occurring at about 65d̀C. Analogously, the profile of intensity of the fluorescence emission at 520 nm of the enzyme‐bound S‐NBD groups versus temperature indicated a midpoint of transition near 65d̀C.Since this melting temperature corresponds closely to that observed with the native enzyme, these results would indicate that the molecular organizations of the native and modified enzyme are similar and stabilized by similar interactions within the polypeptide chain.
SELECTIVE CLEAVAGE AT THE SINGLE TRYPTOPHAN RESIDUE IN BOVINE SOMATOTROPIN BY 2‐(2‐NITROPHENYLSULFENYL)‐3‐METHYL‐3‘‐BROMOINDOLEMINE
Authors: Houghten Richard A. , Li Choh Hao 
Published: August 2010

SELECTIVE CLEAVAGE AT THE SINGLE TRYPTOPHAN RESIDUE IN BOVINE SOMATOTROPIN BY 2‐(2‐NITROPHENYLSULFENYL)‐3‐METHYL‐3′‐BROMOINDOLEMINEThe single tryptophan residue at position 86 in bovine somatotropin has been cleaved by the use of 2‐(2‐nitrophenylsulfenyl)‐3‐methyl‐3′‐bromoindolemine. This reaction was carried out with native bovine growth hormone as well as its reduced and alkylated derivative. When performed on the intact hormone, followed by the reduction and alkylation of the disulfides to liberate the two fragments, the cleavage reaction yielded the fragment containing residues 87–191 in a monomeric state. The other fragment, containing residues 1–86, could only be obtained in a highly aggregated form admixed with other material. When the cleavage reaction was carried out on the reduced and alkylated hormone, both the N‐terminal fragment of reduced‐carbamidomethylated bovine somatotropin as a monomer and the C‐terminal fragment as a dimer were obtained in 35–40% yield. Since the cleavage reaction also oxidized methionine to methionine sulfoxide, the sulfoxides were reduced back to the methionine with N‐methylmercapto acetamide. In this manner the following new derivatives and fragments of bovine somatotropin have been prepared: completely reduced and alkylated hormone, reduced and alkylated hormone with its methionines and tryptophan oxidized, reduced and alkylated hormone with its tryptophan oxidized, the N‐terminal fragment of the hormone containing residues 1–86 with its methionine and tryptophan oxidized, the C‐terminal fragment containing residues 87–191, both with its methionines oxidized and in their native state. The chemical and physical properties of these derivatives and fragments have been determined. Biological activity in the rat tibia was found to be negligible for all derivatives and fragments.
SIDE REACTIONS IN PEPTIDE SYNTHESIS. VI.
Authors: Bodanszky Miklos , Tolle John C. , Deshmane Sharad S. , Bodanszky Agnes 
Published: August 2010

The acid catalyzed O → C migration of the benzyl group in the side chain of tyrosine could be reduced by applying HBr in a mixture of phenol and p‐cresol instead of HBr in trifluoroacetic acid for acidolytic deprotection. This side reaction occurs also during the removal of Boc groups. The loss of O‐benzyl protection and the formation of 3‐benzyltyrosine residues could be suppressed by the application of a 7:3 mixture of trifluoroacetic acid and acetic acid.The acid‐ and base‐catalyzed ring closure of β‐benzylaspartyl residues to aminosuccinyl derivatives was also studied. In this case HBr in trifluoroacetic acid was found to be relatively harmless. Deprotection with HBr in a mixture of trifluoroacetic acid and p‐cresol can be applied for peptides that contain both β‐benzylaspartyl and O‐benzyltyrosyl residues. An attempt to reduce the rate of the base‐catalyzed side reaction by application of hindered tertiary amines was abandoned because the tertiary amines which were effective in this respect led to significant reduction of the rate of the desired reaction, the aminolysis of active esters, as well. A satisfactory solution for the problem was found in the selective catalysis of the active ester reaction with 1‐hydroxybenzotriazole o 4‐dimethylaminopyridine. These catalysts do not enhance the rate of ring closure and in their presence essentially pure β‐benzylaspartyl peptides can be produced in good yield.
PURIFICATION AND CHARACTERIZATION OF THE SURFACE ACTIVE PROTEINS OF BLACK GRAM (PHASEOLUS MUNGO)
Authors: Susheelamma N.S , Rao M.V.L. 
Published: August 2010

The surface active globulin from black gram has been resolved into two components with high foam‐forming activity. They were found to be homogeneous by electrophoresis and ultracentrifugal examinations and had high molecular weights around 100,000 daltons.They were rich in acidic as well as basic amino acids but low in sulphur amino acids. Heat treatment, proteolysis and treatment with certain inorganic salts such as copper, and mercurous mercury, group specific reagents P‐chloromercury benzoate and N‐ethylmalemide (PCMB, NEM) and protein denaturants were found to have an adverse effect, while oxidizing agents had no effect. The free sulphydryl content was low (3 and 4 μmol/mol), but essential for full manifestation of surface activity. Other purified proteins also needed free sulphydryl groups.
ALKALINE ISOMERIZATION OF HORSE AND YEAT CYTOCHROMES C
Authors: Looze Yvan , Polastro Enrico , Deconinck Marc , Leonis Jose 
Published: August 2010

Spectrophotometric studies of the alkaline isomerization of horse heart and yeast cytochrome c show that the haemoproteins from Saccharomyces cerevisiae differ significantly from the mammalian cytochrome c.Apparent pKa values of 8.41, 8.40 and 8.73 for iso‐l‐ (the methylated and unmethylated forms) and iso‐2‐cytochrome c respectively, from baker's yeast were determined and compared with the value of 9.40 found for horse heart cytochrome c.The transitions, measured by observing the decrease of the absorbance at 695 nm as the pH increases, have been found to strictly parallel the decrease in amplitude of the negative circular dichroism band centered at 417 nm. This observation gives additional evidence that this negative band is closely related to the ligation of the heme iron by the sulfur atom of methionine 8u for each of the four haemoproteins examined.
SPECTRAL STUDIES ON TWO GENETIC FORMS OF THE HUMAN SERUM PROTEINASE INHIBITOR, ALPHA‐1‐ANTITRYPSIN*
Authors: Glaser Charles B. , Karic Lucija 
Published: August 2010

Alpha‐1‐antitrypsin, the major inhibitor of proteolytic enzymes in human serum, was isolated from normal individuals (protease inhibitor type MM) and from those with an inherited deficiency (protease inhibitor type ZZ) of circulatory protein.The two proteins were compared by circular dichroism spectroscopy, and by fluorescence quenching experiments using anionic (I‐), and neutral (acrylamide) probes.Both proteins share a similar secondary structure, i.e. ˜45–50%α‐helix and 15–20%β‐structure. Evidence was accumulated to show that the micro‐environment in the vicinity of the three tryptophanyl residues is altered in Z form as compared to the M form as shown by (a) the absence of the positive dichroic band in the region 290–300nm of the circular dichroism spectra, (b) a > 50% increase in quantum yield in the tryptophanyl fluorescence emission spectra, (c) an increased accessibility of tryptophan to quenching by iodide, and (d) acrylamide quenching experiments which indicate that all tryptophanyl residues in the Z protein are quenched equally or that quenching is dominated by a single residue, while in the M protein, heterogeneous quenching occurs. The potential significance of these findings in terms of alpha‐1‐antitrypsin deficiency state are discussed.
PROTEIN DENSITIES
Authors: KUNTZ I.D. , CRIPPEN G.M. 
Published: August 2010

The calculation of protein densities from atomic coordinates is not straightforward and requires very careful attention to the determination of the protein‐solvent boundary. Interior densities are more readily obtained and are in reasonable agreement with those estimated from solvent accessibility studies.The interior of globular proteins has very significant density inhomogenities on a scale of 100–1000 Å3. The interior densities range from less than 0.5 g/cm3 to over 3 g/cm3. The low local densities are primarily associated with clusters of nonpolar sidechains while the high local density regions arise from the protein backbone secondary structures: helices and beta sheets. We show a rough correlation between local density and local polarity.
STUDIES ON TRYPSIN INHIBITORS Part IX. Synthesis and Trypsin Inhibitory Activity of the Duopentacontapeptide Corresponding to the Amino Acid Sequence of Porcine Pancreatic Secretory Trypsin Inhibitor II (Kazal)*
Authors: TOMATIS ROBERTO , GUARNERI MARIO , GUGGI AUGUSTO , SALVADORI SEVERO , ROCCHI RANIERO 
Published: August 2010

The synthesis of the protected duopentacontapeptide corresponding to the entire amino acid sequence 1–52 of porcine pancreatic secretory trypsin inhibitor II (Kazal type) is described.The benzyloxycarbonyltetradecapeptide tert‐butyloxycarbonylhydrazide (sequence 1–14) was selectively deblocked with trifluoroacetic acid and used to acylate, by the azide procedure, the peptide free base corresponding to the sequence 15–52. The isolated material was purified by ion exchange chromatography and the protecting groups were removed by successive treatments with anhydrous hydrogen fluoride, 1M piperidine and mercuric acetate.Folding and formation of the disulfide bonds was accomplished by air oxidation in 0.02M phosphate buffer, pH8.Determination of the inhibitory capacity indicated that the synthetic material is about 50% effective, at 30:1 inhibitor:trypsin molar ratio, in inhibiting the tryptic hydrolysis of Nα‐benzoyl‐dl‐arginine‐4‐nitroanilide. Full inhibition was achieved at a higher inhibitor:trypsin molar ratio. The stability constants and the standard free energy of binding of the complex between trypsin and the synthetic inhibitor have been determined.
COMPARATIVE STUDY OF THE NEUROHYPOPHYSEAL HORMONE [8‐ARGININE] VASOPRESSIN AND ITS ANALOG [7‐(3,4‐DEHYDROPROLINE), 8‐ARGININE] VASOPRESSIN IN AQUEOUS SOLUTION: An Examination of the Nonlabile Protons by1H Nuclear Magnetic Resonance Spectroscopy
Authors: WYSSBROD HERMAN R. , FISCHMAN ALAN J. , WITTBOLD WILLIAM M. , SMITH CLARK W. , WALTER RODERICH , SCHWARTZ I.L. 
Published: August 2010

[7‐(3, 4‐Dehydroproline), 8‐arginine]vasopressin ([Δ3‐Pro7]AVP), an active analog of the naturally occurring neurohypophyseal hormone [8‐arginine]vasopressin (AVP), was studied in D2O at pD 3.3 and 23° by1H n.m.r. spectroscopy, and chemical shifts (SdLs) and some of the coupling constants for the nonlabile protons (1Hs) were determined and compared to those previously reported by us for AVP in D2O at pD 3.8 and 20° (Wyssbrod et al., 7979a, b). Double‐ resonance difference spectroscopy (Gibbons et al., 1975) was used to reveal positions of certain resonances obscured by overlap with resonances of other1Hs.Values of δ of corresponding protons in [Δ3‐Pro7]AVP and AVP are quite similar, and the small differences that are observed can be explained on the basis of (a) magnetic anisotropy from the double bond in the Δ3‐prolyl residue, (b) a slight difference in acidity of the samples in the two studies, or (c) uncertainty in the experimentally determined value of δ. Values of δ for the1Hs in the Δ3‐prolyl and prolyl residues in the two peptides are reported.Our tentative conclusion is that the differences in reported biological activities of [Δ3‐Pro7]AVP and AVP (Botos et al., 1979) are probably not[Δ3‐PRO7, ARG8] VASOPRESSIN related to a perturbation in the conformational state of the backbone, but that they might be explained, in part, by a change in the conformation of the five‐ membered ring of residue 7 and, in part, by π‐π interaction between the 3‐pyrroline ring of the Δ3‐prolyl residue of [Δ3‐Pro7]AVP and the receptor involved in the antidiuretic response but not the receptor involved in the pressor response, in accordance with the suggestion of Walter (1977) that π‐π interactions might, in some cases, be involved in binding of a peptide to its receptor.
SYNTHESIS OF 8‐L‐TRYPTOPHAN‐OXYTOCIN AND DETERMINATION OF ONE OF ITS CONFORMATIONAL PARAMETERS
Authors: BODANSZKY MIKLOS , TOLLE JOHN C. , BEDNAREK MARIA A. , SCHILLER PETER W. 
Published: August 2010

The hormone analog 8‐l‐tryptophan‐oxytocin was synthesized in solution by stepwise chain lengthening from the C‐terminal residue. Active esters of 9‐fluorenylmethyloxycarbonyl (Fmoc)‐amino acids were used for the incorporation of individual residues and thereby exposure of the tryptophan‐containing intermediates both to acid conditions and to alkylation could be avoided. In a parallel experiment the parent compound, oxytocin, was prepared similarly. The final products were purified by countercurrent distribution.The presence of tyrosine (donor) and tryptophan (acceptor) in the chain was used for the measurement of the average intramolecular Tyr2‐Trp8 distance by evaluation of intramolecular resonance energy transfer between their fluorescent side chains. Since the 8‐l‐tryptophan analog has high affinity for oxytocin receptors, it is reasonable to assume that its conformation is similar to that of the parent molecule and that in the latter the leucine‐tyrosine distance is of about the same length. The distance of 13.5 Å between the side chains of tyrosine and tryptophan measured in aqueous solution is compatible with the Tyr2‐Leu8 distance determined with molecular models built according to the proposals of Walter for the biologically active conformation of oxytocin.
Differentiation of the structural features of melanotropins important for biological potency and prolonged activity in vitro
Authors: WILKES BRIAN C. , SAWYER TOMI K. , HRUBY VICTOR J. , HADLEY MAC E. 
Published: August 2010

Several α‐melanotropin (α‐MSH) analogues have been synthesized and tested for their melanotropin activities in order to determine the functional importance of certain amino acids near the primary active sequence of α‐MSH, H‐(Glu)‐His‐Phe‐Arg‐Trp‐Gly‐OH, on the biological activities of the hormone. In particular, we have examined the importance of the 4 and 11 positions in conjunction with the substitution of l‐Phe in position 7 by d‐Phe on potency and prolonged activity of the hormone. In the frog (Rana pipiens) skin system the relative potencies were found to be: [Nle4, d‐Phe7]‐α‐MSH (60) > α‐MSH (1.0) > Ac‐[Nle4, d‐Phe7]‐α‐MSH4–11‐NH2 (0.16) > Ac‐[Nle4, d‐Phe7]‐α‐MSH4–10‐NH2 (0.02) · Ac‐[d‐Phe7]‐α‐MSH5–11‐NH2 (0.01) > Ac‐[Nle4]‐α‐MSH4–10‐NH2 (0.002) = Ac‐[Nle4]‐α‐MSH4–11‐NH2 > Ac‐α‐MSH4–10‐NH2 (0.0003) · Ac‐α‐MSH5–11‐NH2 (0.0002). On the other hand the relative potencies on the lizard (Anolis carolinensis) skin system were found to be: Ac‐[Nle4, d‐Phe7]‐α‐MSH4–10‐NH2 (10) · Ac‐[Nle4, d‐Phe7]‐α‐MSH4–11‐NH2 (8.0) · Ac‐[Nle4, d‐Phe7]‐α‐MSH (5.0) > α‐MSH (1.0) = Ac‐[Nle4]‐α‐MSH4–11‐NH2 = Ac‐[d‐Phe7]‐α‐MSH5–11‐NH2 > Ac‐[Nle4]‐α‐MSH4–10‐NH2 (0.06) > Ac‐α‐MSH5–11‐NH2 (0.01) > Ac‐α‐MSH4–10‐NH2 (0.004). Detailed analyses of these data suggest species‐dependent differences in the stereostructural relationships of the residues in the 4, 7, and 11 positions for melanotropic potency in vitro. Particularly noteworthy is the observation that the 4–11 fragment analogue Ac‐[Nle4]‐α‐MSH4–11‐NH2 is equipotent to α‐MSH in the lizard assay system, suggesting that the 1–3, 12, and 13 residues of α‐MSH are not involved in the binding or transduction in this system.Examination of the ability of these α‐melanotropin analogues to effect sustained biological activity (prolongation) following removal of exogenous peptide from the bioassay medium showed striking differences in the two systems. On the lizard skin assay, only [Nle4, d‐Phe7]‐α‐MSH, Ac‐[Nle4, d‐Phe7]‐α‐MSH4–11‐NH2 and Ac‐[Nle4, d‐Phe7]‐α‐MSH4–10‐NH2 effect marked prolonged melanotropic activity as compared to α‐MSH. In contrast, on the frog skin assay, only [Nle4, d‐Phe7]‐α‐MSH, Ac‐[Nle4, d‐Phe7]‐α‐MSH4–11‐NH2, Ac‐α‐MSH5–11‐NH2, and Ac‐[Nle4]‐α‐MSH4–10‐NH2 exhibited significant prolonged activity. These results demonstrate that relative potency and prolongation of melanotropic activity are not directly related, but rather are the manifestation of different, species‐dependent structural and topographical requirements for peptide‐receptor interactions related to binding and signal transduction.
Assignments of the 270 MHz PMR spectrum of somatostatin using pH titration, synthetic analogs and double resonance difference spectroscopy
Authors: BUFFINGTON LYNN A. , GARSKY VICTOR , RIVIER JEAN , GIBBONS WILLIAM A. 
Published: August 2010

We report the assignment procedure for the 270 MHz PMR spectrum in D2O of the 14 amino acid peptide hormone somatostatin,Ala1 Gly2 Cys3 Lys4 Asn5 Phe6 Phe7 Trp8 Lys9 Thr10 Phe11 Thr12 Ser13 Cys14using a series of synthetic analogs in which a single amino acid residue was replaced by an Ala residue. The principal methods used were pH titration and extensive double resonance experiments (difference scalar decouplings and nuclear Overhauser effect measurements).
Mechanism of the reaction catalyzed by acyl‐CoA: lysolecithin acyltransferase from rabbit lung.
Authors: ESTRADA P. , ACEBAL C. , ARCHE R. 
Published: August 2010

This paper deals with the first attempt to elucidate the chemical mechanism of acyl‐CoA:lysolecithin acyltransferase from rabbit lung, a key enzyme in the metabolism of lung surfactant. For this purpose, the pH dependence of kinetic constants as well as the chemical modification of the protein have been studied on a partially‐purified preparation.From these experiments, the pKs on which the activity of the enzyme relies have been calculated, giving values of pK1 ⋍ 5.5 and pK2 ⋍ 10. Analysis of the effect of organic solvents on these pKs and the calculation of the enthalpies of ionization, together with the chemical modification experiments, lead to the conclusion that pK1 is due to an histidine residue, whereas pK2 arises from the amino group of the adenine ring of palmitoyl‐CoA. Moreover, chemical modification demonstrated an essential cysteine.A tentative chemical mechanism, in accordance with these results, is proposed and it is hypothesized, in view of other results obtained in our laboratory and from the literature, that the chemical mechanism of acyl transfer to sn‐2 position may be common to other enzymes of glycerolipid metabolism.
Synthesis and conformational studies on peptides corresponding to a putative autophosphorylation site of abl TPK*
Authors: RUZZA PAOLO , CALDIIRAN ANDREA , FILIPPI BRUNO , DONELLA‐DEANA ARIANNA , PINNA LORENZO A. , BORIN GIANFRANCO 
Published: August 2010

The transforming gene of Abelson murine leukaemia virus (v‐abl) codes for a membrane‐associated tyrosine‐specific protein kinase (abl TPK). Analysis of the v‐abl gene has shown that both the fibroblast‐transforming and tyrosine‐protein kinase activities reside within a minimal region encoding a protein of 43 kDa (p43v‐abl), which represents the most active, isolated form of this enzyme. Since the cellular substrates for p43 v‐abl are yet to be identified, we synthesized by classical solution methods the octapeptide H‐Gly‐Asp‐Thr‐Tyr‐Thr‐Ala‐His‐Ala‐OH, corresponding to the structural sequence of the main putative autophosphorylation site (Tyr 515) of the abl TPK, as well as some of its analogs modified in positions ‐2, ‐1, + 1 and + 3.The synthetic peptides were tested as substrates for the p43v‐abl. The kinetic data obtained indicate that the rates of their phosphorylation vary considerably depending on the sequence of the peptide, as expected. As a rule, no significant increment of the efficiency results from each substitution in the parent sequence. While the replacement of the two charged residues, namely Asp‐2 and His‐7, with neutral Ala is well tolerated, the substitution with amino acids bearing opposite charges is detrimental. The correlation between secondary structure of our synthetic octapeptides and their substrate recognition by p43v‐abl was studied using CD and fluorescence spectroscopy in 5 mM Tris, in 98% TFE/Tris and in 30 mM SDS solutions. The comparison of the spectroscopic data with the kinetic parameters does not confirm a close relationship between the conformational properties of these peptides and their enzymatic role.