bluuebunny/crossref_metadata_2025 huggingface dataset:
Solution conformations of oligomers of α ‐aminoisobutyric acid°
Authors: PATERSON YVONNE , STIMSON EVELYN R. , EVANS DAVID J. , LEACH SYDNEY J. , SCHERAGA HAROLD A.
Published: August 2010

The N‐acetyl(Aib)nN' ‐methylamides (with n= 1, 2 and 3) and the N‐acetyl‐(Aib)3 methyl ester have been synthesized using an oxazolone procedure. An experimental conformational analysis of this series of oligomers has been carried out in water, DMSO‐d6 and CDCI3 using n.m.r. techniques, and in chloroform using i.r. spectroscopy. Deuterium exchange rates of amide protons in DMSO‐d6 and the rates of change of these proton chemical shifts with temperature in water, DMSO‐d6 and CDCI3 indicate that the oligomeric N'‐methylamides adopt conformations that have no hydrogen bonds when n = 1, one hydrogen bond when n = 2, and two hydrogen bonds when n = 3, and that Ac(Aib)3OMe has a conformation with one hydrogen bond. An analysis of the N‐H stretching region of the i.r. spectra of these compounds in CHCI3 also suggests the existence of these conformational states. These data imply that the peptides adopt the 310‐helical and not the α‐helical conformation in solution. This conclusion supports the hypothesis that the Aib residue has asymmetric geometry at the Cα atom in solution, similar to that reported in the literature for the crystalline state.
Amino acid sequence of the tryptic SH‐peptide of thermitase, a thermostable serine proteinase from Thermoactinomyces vulgaris. Relation to the subtilisins
Authors: BAUDYŠ M. , KOSTKA V. , HAUSDORF G. , FITTKAU S. , HÖHNE W.E.
Published: August 2010

The following amino acid sequence of the tryptic SH‐peptide of thermitase, a thermostable serine proteinase from Thermoactinomyces vulgaris, was determined: Val ‐ Val ‐ Gly ‐ Gly ‐ Trp ‐ Asp ‐ Phe ‐ Val‐Asp‐Asn‐Asp‐Ser‐Thr‐Pro‐Gln‐Asn ‐ Gly ‐ Asn ‐ Gly ‐His64‐ Gly ‐ Thr ‐ His ‐Cys68 ‐ Ala‐Gly‐Ile‐Ala‐Ala‐Ala‐Val‐Thr‐Asn ‐ Asn ‐ Ser ‐ Thr ‐ Gly ‐ Ile ‐ Ala ‐ Gly ‐ Thr ‐ Ala ‐ Pro ‐ Lys. This sequence shows homology with the highly conservative part of the subtilisin sequences around the active site His‐64. The single cysteine residue of thermitase is localized near this histidine residue thus replacing valine in position 68 (according to the numbering of the subtilisins). This becomes evident also from the specific labeling of the active site histidine with a radioactive inhibitor (Z‐Ala‐Ala‐Phe‐14CH2‐Cl). The tryptic SH‐peptide isolated from the modified enzyme contains all the radioactivity and has the same end group and amino acid composition as the tryptic peptide isolated from the tryptic digest of the unlabeled enzyme and subjected to sequential analysis. From sequence homology as well as from secondary structure predictions it may be concluded that the geometry of the active site of thermitase is very similar to that of the subtilisins with the cysteine residue nearby. The inactivation of thermitase by labeling of the SH‐group with mercury compounds may then be due to a sterical hindrance or to a more direct interaction of the mercury atom with the charge relay system of the enzyme.
Conformational properties of pairs of amino acids
Authors: KOLASKAR A.S. , RAMABRAHMAM V.
Published: August 2010

Crystal structure data of 31 different globular proteins were analysed. Potentials for all 400 pairs of 20 amino acid residues in helix, extended structure, chain reversals and coil state were obtained. Analysis of these potentials showed that tripeptides of amino acid residues are not linear combinations of amino acids. The association effect of these tripeptides depends on the types of amino acids associated, the position of amino acids in the pair and the secondary structure in which the pair exists. This built‐in information in tripeptides should be used in polypeptide and protein folding studies.
Occurrence and geometrical features of head‐to‐tail sequences involving amino acids in crystal structures
Authors: SURESH C. G. , VIJAYAN M.
Published: August 2010

A careful study of the crystal structures of commonly occurring amino acids, and their racemates and complexes reveals that each hydrogen bond connecting the α‐amino and the α‐carboxylate groups and its symmetry equivalents generally give rise to an infinite head‐to‐tail sequence in which the two groups are periodically brought into close proximity. Such sequences, which have earlier been suggested to be of probable relevance to prebiotic polymerisation, appear to be an almost universal feature of amino acid aggregation in the solid state. These sequences belong to two main categories in terms of the geometrical arrangement of amino acid molecules in them. The sequences in the first category consist of straight chains of molecules related mostly by the shortest cell translation in the crystals. The sequences of the second category form hydrogen bonded two fold helices centred around crystallographic 21 screw axes. The sequences can be further sub‐divided into different types on the basis of the geometrical features of the hydrogen bonds involved in them. A few sequences involving both l and d isomers have also been observed in the crystal structures of some dl‐amino acids. The shortest cell translation in most crystals under consideration has a value in the neighbourhood of 5.3 Å and corresponds to the periodicity of a straight head‐to‐tail sequence or, less frequently, that of a helical sequence or both. The crystal structures of amino acids and their complexes can be classified in terms of the occurrence and the geometrical disposition of different types of head‐to‐tail sequences in them.
A cleavable cross‐linking reaction for protein carboxyl groups
Authors: RENTHAL ROBERT
Published: August 2010

l‐(+)‐tartaric acid dihydrazide was coupled to the purple membrane from Halobacterium halobium with a water soluble carbodiimide. Gel electrophoresis analysis of the product revealed the formation of bacteriorhodopsin dimers, trimers and higher polymers. Most of the cross‐links were removed by treatment with papain, demonstrating involvement of the carboxyl‐rich carboxyl‐terminal region of bacteriorhodopsin in the reaction. The cross‐links were cleavable by periodate oxidation.
α‐Scorpion neurotoxin derivatives suitable as potential markers of sodium channels. Preparation and characterization
Authors: DARBON HERVÉ , JOVER EMMANUEL , COURAUD FRANÇOIS , ROCHAT HERVÉ
Published: August 2010

Modified scorpion neurotoxins, i.e. mono‐biotinylated and mono‐azido derivatives either on lysine 58 or lysine 60 have been characterized both at the structural level (sequence and circular dichroism) and by their pharmacological activity (toxicity to mice and ability to displace 125I‐Androctonus australis Hector toxin II from its receptor sites. The results allowed us to pinpoint a region of the molecule including lysine residues 58 and 60 that is important for neurotoxin receptor interaction. Furthermore, as these derivatives retain, after 125I labeling, high binding capacities to synaptosomal membranes, they can be used as potential labels of the sodium channel either by covalent binding or using the avidin‐biotin system.
Synthesis of some 3‐hydroxynaphthalene‐2‐carbonylamino acid and dipeptide derivatives
Authors: EL‐NAGGAR A.M. , AHMED F.S.M. , BADIE M.F. , KAMEL K.M.
Published: August 2010

Synthesis of a series of 3‐hydroxynaphthalene‐2‐carbonylamino acid methyl esters (II‐XI) and some of their corresponding hydrazides (XII‐XXI), dipeptide methyl esters (XXII‐XXXV) and dipeptide hydrazides (XXXVI‐XXXIX) is described. 3‐Hydroxynaphthalene‐2‐CO‐l‐Tyr‐N2H3 (XX) and the corresponding l‐Val‐l‐Ala‐N2H3 (XXXVI) were found to be active against a number of microorganisms.
Conjugates of catecholamines. III. Synthesis and characterization of monodisperse oligopeptides conjugates related to isoproterenol
Authors: JACOBSON K.A. , VERLANDER M.S. , ROSENKRANZ R.P. , MELMON K.L. , GOODMAN M.
Published: August 2010

A series of monodisperse oligopeptide conjugates related to the catecholamine, isoproterenol, has been synthesized. The peptide carrier molecules used were synthesized by stepwise and fragment condensation techniques and ranged in size from a single, blocked amino acid derivative to isomeric pentapeptides. The amino acid compositions and sequences of the carriers were chosen so as to provide specific information concerning the effects of molecular weight, hydrophilic/hydrophobic balance, charge, etc., on the biological activity of the final conjugates. The common point of attachment for the drug in all carriers was a p ‐aminophenylalanine residue. The peptide‐catecholamine conjugates were prepared via the attachment of carboxyl‐containing catecholamine congeners, to the peptide carriers by techniques described previously. The conjugates were purified rigorously by chromatographic techniques and characterized by high‐field n.m.r. spectroscopy.
Protected 1–3 segment of the peptaibol antibiotics alamethicin and hypelcin.
Authors: BENEDETTI ETTORE , BAVOSO ALFONSO , DI BLASIO BENEDETTO , PAVONE VINCENZO , PEDONE CARLO , TONIOLO CLAUDIO , BONORA GIAN MARIA , CRISMA MARCO
Published: August 2010

A study of the modes of folding and self‐association of Z‐Aib‐l‐Pro‐Aib‐OMe (the protected 1–3 segment of the peptaibol antibiotics alamethicin and hypelcin) in the solid state was performed using i.r. absorption and X‐ray diffraction. The stereochemically constrained tripeptide molecules adopt a 4 ± 1 intramolecularly H‐bonded form (β‐turn), where the single intramolecular H‐bond is found between the peptide N‐H group of the Aib3 residue and the urethane C = O group of the N‐blocking benzyloxycarbonyl moiety. This folded structure is stabilized by an intermolecular H‐bond between the urethane N‐H group of the Aib1 residue and the peptide C = O group of the Pro2 residue of a symmetry related molecule. According to the i.r. absorption data, in CH2Cl2 and TMP solutions the same intramolecularly H‐bonded form occurs as that found in solid state. Compared to the situation in the solid state, in CH2Cl2 and TMP solvation of the urethane N‐H group replaces self‐association (through the same N‐H group). The results are also discussed in relation to those obtained for other protected ‐Aib‐X‐Aib‐(X = Aib, l‐Ala, l‐Val) tripeptide segments of peptaibol antibiotics.
A new enkephalin analogue: trans‐4‐hydroxycinnamoyl‐glycyl‐glycyl‐phenylalanyl‐leucine. Synthesis and biological properties
Authors: AMAR CLAUDINE , V1LKAS ERNA , LAURENT STEPHANE , GAUTRAY BRUNO , SCHMITT HENRI
Published: August 2010

A new analogue of the leucine‐enkephalin in which the N ‐terminal tyrosine has been replaced by trans ‐4‐hydroxycinnamic acid, has been synthetized by liquid‐phase coupling methods. The central cardiovascular effects of this analogue were investigated and the results discussed.
Structural basis for the thermal stability of glyceraldehyde‐3‐phosphate dehydrogenases
Authors: OLSEN KENNETH W.
Published: August 2010

The amino acid sequences of two thermophilic and five mesophilic glyceralde‐hyde‐3‐phosphate dehydrogenases have been compared with the known three‐dimensional structure of this enzyme to determine the factors responsible for thermal stability. The changes are greatest in the S‐loop regions at the center of the tetramer, which show a quantitative increase in hydrophobicity and polarity that can strengthen subunit interactions in a complementary manner. The S‐loops also show increases in residue volume and bulk that may indicate a tighter packing at the molecular center. In addition, there are changes in the secondary structural parameters indicating that the helices, in particular, may be more stable in the thermophilic proteins. Increases in the hydrophobicity of domain and subunit contacts for the Thermus aquaticus glyceraldehyde‐3‐phosphate dehydrogenase may explain why it is the most thermostable protein in this series.
Synthesis and 19F spectra of tetra‐L‐alanine analogs containing selectively incorporated 3‐fluoro‐l‐alanine residues
Authors: MITRA ALOK K. , OSTASHEVSKY IOSIF , BREWER CURTIS F.
Published: August 2010

The synthesis of analogs of tetra‐l‐alanine containing 3‐fluoro‐l‐alanine selectively incorporated at each position is described. The standard procedures in the literature used to couple l‐alanine peptides together were often found to lead to undesired products, or elimination reactions when corresponding 3‐fluoro‐l‐alanine peptide analogs were used. Several modified procedures have thus been developed for the synthesis of fluorine‐substituted analogs. In addition, the pH‐dependence of 19F n.m.r. spectra of 3‐fluoro‐l‐alanine and the tetrapeptide analogs is presented.
13 C n.m.r. study of l‐alanine peptides
Authors: MITRA ALOK K. , OSTASHEVSKY IOSIF , BREWER CURTIS F.
Published: August 2010

The di‐, tri, and tetrapeptides of l‐alanine have been studied in aqueous solution by 13C n.m.r. spectroscopy at 25 and 50 MHz. By using selectively 13C enriched analogs containing either 90% 13C methyl or carbonyl carbons and measurements as a function of pH, assignment of the chemical shifts of the peptides has been made. T1 and NOE measurements of the peptides in their cationic, anionic, and zwitterionic states have been recorded as a function of concentration. The results show considerable segmental motion along the backbone carbons of the peptides, with only small changes occurring in the dynamic motions of the peptides as their charge states are altered. The lack of concentration dependence of the chemical shift and T1 values, as well as the similarity of T1 values for individual peptides in the three charge states, indicate that the peptides do not self‐associate in aqueous solution.
Hierarchic organization of globular proteins
Authors: Yuschok Thomas J. , Rose George D.
Published: August 2010

In previous work, globular proteins of known structure were shown to be iteratively subdivisible into a hierarchy of disjunct, contiguous‐chain regions, ranging in size from whole protein monomers down to individual helices and strands (1, 2). We now report the results of a similar analysis performed on a set of 1000 simulated chain folds that were generated by a method due to Schulz (3). The organization of these simulated proteins was found to be similar to that of authentic molecules. This control study strengthens earlier evidence suggesting that hierarchic architecture is a ubiquitous attribute of protein chain folds.
Origin of slow conformer conversion of triostin A and interaction ability with nucleic acid bases
Authors: HIGUCHI NAOKI , KYOGOKU YOSHIMASA , SHIN MASARU , INOUYE KEN
Published: August 2010

The n.m.r. pattern of triostin A in weakly polar solvents was expalined by the presence of two symmetrical conformers. Its S‐benzyl derivative still shows the n.m.r. pattern of two conformers, while des‐N‐tetramethyltriostin A, which lacks the N‐methyl groups, gives one conformer. Therefore the slow interconversion of two conformers arises from the cis‐trans isomerization of the N‐methyl peptide bonds, but not from the reversal of the chirality around the S‐S bond. Only one of the two conformers of triostin A interacts with adenosine and guanosine derivatives. Des‐N‐tetramethyltriostin A can also interact with the purine nucleosides, but more preferentially with the adenosine derivative.
A facile synthesis of β‐(S‐benzylmercapto)‐β,β‐cyclopentamethylenepropionic acid
Authors: YIM NELSON C.F. , HUFFMAN WILLIAM F.
Published: August 2010

The title compound is a key intermediate for the preparation of oxytocin and vasopressin antagonists. Using sodium benzylmercaptide instead of boron trifluoride etherate as catalyst gives a better than four fold overall improvement in yield of the title compound from ethyl cyclohexylideneacetate and benzyl‐mercaptan. The preparation of the corresponding acid labile S‐p‐methylbenzyl‐mercapto and S‐p‐methoxybenzylmercapto analogs is also described.
Conformational studies of cyclic tetrapeptides
Authors: RICH DANIEL H. , KAWAI MEGUMI , JASENSKY RONALD D.
Published: August 2010

The conformations of chlamydocin and cyclo (Ala‐Aib‐Phe‐D‐Pro)(Ala4‐chlamy‐docin) in chloroform have been investigated by nuclear magnetic resonance, infrared and circular dichroism spectroscopy. The data obtained from these experiments establish an all transoid, bis γ‐turn conformation for both compounds in chloroform with the following torsional angles (± 20d̀): Ala44‐chlamydocin: Aib, Ø+ 60d̀, Ψ– 50d̀; ω+ 160d̀; Phe Ø– 120d̀, Ψ+ 120d̀, ω– 160d̀; D‐Pro Ø+ 60d̀, Ø– 55d̀, ω+ 160d̀; Ala Ø– 110d̀, Ψ+ 110d̀, ω– 160d̀. Chlamydocin adopts a closely related conformation in neat chloroform. Nuclear Overhauser Effect (NOE) data are utilized to assign amide bond geometries in the cyclic tetrapeptide ring system.
Domain characteristics of the cyanogen bromide fragment 121–316 of thermolysin
Authors: VITA CLAUDIO , DALZOPPO DANIELE , FONTANA ANGELO
Published: August 2010

The molecule of thermolysin was shown by X‐ray crystallography to be composed of two structural domains of equal size comprising residues 1–157 and 158–316. In order to explore the possibility that these domains correspond to globular fragments able to refold autonomously, we have investigated the conformational and stability properties of fragment 121–316, which was obtained by limited chemical cleavage of thermolysin with cyanogen bromide. As judged by far‐ultraviolet circular dichroism measurements, in aqueous solution under neutral conditions the fragment maintains a relative amount of helical structure which is comparable to that exhibited by the corresponding region in native thermolysin. The secondary structure attained by the fragment appears remarkably stable to the denaturing action of heat. By measuring the temperature dependence of the dichroic signal at 220 nm a Tm near 74d̀ was obtained. Immunodiffusion analyses indicated that the fragment recognizes and precipitates antibodies raised in rabbits using native thermolysin as immunogen. The overall conformational and immunochemical data indicate that fragment 121–316 of thermolysin is able to refold into a stable structure of native‐like characteristics independently of the rest of the molecule. The results of this study complement those previously reported for fragment 206–316 (Vita, C., Fontana, A., Seeman, J.R. & Chaiken, I.M. (1979) Biochemistry18, 3023–3031).
Synthesis of [1, 6‐cyclo(Acetyl‐1‐L‐glutamic acid, 2‐D‐phenylalanine, 3‐D‐tryptophan, 6‐D‐lysine)] luteinizing hormone‐releasing hormone on poly‐N‐acrylylpyrrolidine resin
Authors: SMITH CLARK W. , SKALA GERALD , WILKS JOHN W.
Published: August 2010

The protected peptide, Ac‐Glu(OBut)‐D‐Phe‐D‐Trp‐Ser(But)‐Tyr(But)‐D‐Lys(Z)‐Leu‐Arg(Tos)‐Pro‐Gly‐NH2 was synthesized in a stepwise manner on a resin of poly‐N‐acrylylpyrrolidine using both acid cleavable Nα‐tert.‐butyloxy‐carbonyl and base cleavable Nα‐fluorenylmethyloxycarbonyl protecting groups. After cleavage by ammonolysis in methanol, the tert.‐butyl and benzyloxy‐carbonyl side‐chain protecting groups were cleaved with CF3‐CO2H‐thioanisole and the 1–6 amide ring formed by cyclization with diphenylphosphorylazide, after which the remaining tosyl protecting group was cleaved in HF‐anisole. [1,6‐Cyclo (Ac‐Glu1, D‐Phe2, D‐Trp3, D‐Lys6] LH‐RH exhibited less than 10% of the antiovulatory potency of [D<Glu1, D‐Phe2, D‐Trp3,6] LH‐RH, a potent linear antagonist.
X‐ray studies on crystalline complexes involving amino acids and peptides
Authors: SURESH C.G. , VIJAYAN M.
Published: August 2010

L‐Arginine acetate crystallizes in the monoclinic space group P21 with a = 9.229(2), b = 5.178(3), c = 13.271(4) Å and β= 111.4(1)d̀. The crystal structure was solved by direct methods and refined to an R value of 0.058 for 1333 observed reflections. The conformation of the arginine molecules in the crystal is different from those observed in the crystals of L‐arginine, its salts and complexes. The crystal structure indicates that complexation with a small carboxylic acid like acetic acid is sufficient to align arginine molecules in a head‐to‐tail fashion. The structure contains a specific ion‐pair interaction, involving electrostatic attraction as well as two nearly parallel, N‐H. O hydrogen bonds, between the guanidyl group and the acetate ion.
Synthesis and backbone conformations of cyclic hexapeptides cyclo‐(Xxx‐Pro‐D‐Gln)2
Authors: KOPPLE KENNETH D. , PARAMESWARAN KUMARAMPURAM N.
Published: August 2010

The solution syntheses of cyclo‐(Xxx‐Pro‐D‐Gln)2, where Xxx=Gly, Ala, Leu, Phe and Val are described. Several routes were examined, the most successful involving the intermediate Z‐Xxx‐Pro‐D‐Gln‐O‐tBu and proceeding to cyclization of H‐Xxx‐Pro‐D‐Gln‐Xxx‐Pro‐D‐Gln‐OH using diphenylphosphoryl azide. The N‐H regions of the proton magnetic resonance spectra of aqueous solutions of these peptides were examined, and in the Xxx=Leu and Val peptides an unsymmetrical backbone, presumably with one cis Xxx‐Pro peptide bond, was found to be important. Previous reports of cyclo‐(Xxx‐Pro‐D‐Yyy)2 peptides have shown only C2‐symmetric forms.
Synthesis and properties of β‐endorphin analogs containing the dynorphin‐(1–13) sequence
Authors: LI CHOH HAO , YAMASHIRO DONALD , FERRARA PASCUAL , TSENG LIANG‐FU , WAY E. LEONG
Published: August 2010

Two analogs of βh‐endorphin containing dynorphin‐(5 ‐ 13) or dynorphin‐(6 ‐ 13) sequence have been synthesized by the solid‐phase method. Biological activities of the analogs have also been investigated. It was found that the opiate activity is about three times more than βh‐endorphin in the guinea pig ileum assay. Both analgesic potency and opiate receptor‐binding activity of the analogs are lower when compared with βh‐endorphin. However, the analogs have interesting behavioral effects in mice.
ß‐endorphin: synthesis and properties of analogs modified at position 6
Authors: YAMASHIRO DONALD , WESTPHAL MANFRED , HOEY KENWAY , LI CHOH HAO
Published: August 2010

Two analogs of ß‐endorphin (ß‐EP) weresynthesizedby the solid‐phase method: [D‐Ser6]‐ßc‐EP (I) and [Pro6]‐ßc‐EP (II)(ßc‐EP = camel ß‐EP). Radioreceptor binding assay with use of tritiated human ß‐EP (ßh‐EP) as primary ligand gave relative potencies as follows: ßc‐EP, 100; I, 32; II, 28. Relative potencies in ananalgesia assaywere: ßc‐EP, 100; I, 115; II, 31.
Specific modification of carboxyl‐groups in bovine growth hormone by a soluble carbodiimide and glycinemethylester
Authors: DELFINO J.M. , FERNANDEZ H.N. , SANTOMÉ J.A.
Published: August 2010

The reactivity of the carboxyl groups in bovine growth hormone was studied by reaction with 1‐ethyl‐3(3‐dimethylaminopropyl) carbodiimide in the presence of an excess of glycinemethylester. Localization in the molecule of the various kinetically distinguishable carboxyl groups was achieved. Highest reactivity was found in carboxyl groups 30, 125, 127 and 128. These residues were followed, as to reactivity, by a set including carboxyl groups 65, 105, 151, 152, 185 and 190. Modification of approximately one fifth of the carboxyl groups in bovine growth hormone led to an important decrease in its growth promoting activity and capacity to compete with125I‐labeled growth hormone for rat liver binding sites. Demethoxylation restored most of the original biological activity.
Ethoxyformylation of bovine growth hormone
Authors: FUKUSHIMA J.G. , BONINO M.J. BISCOGLIO DE JIMENEZ , CASCONE O. , SANTOMÉ J.A.
Published: August 2010

Reactivity of histidines in bovine growth hormone towards ethoxyformic anhydride was investigated and localization in the molecule of two kinetically distinguishable classes was achieved, a slow class including only histidine residue 169 (k = 0.180 min‐1) and a fast one composed of histidines 19 and 21 (k = 0.900 min‐1). Total ethoxyformylation of bovine growth hormone brought about a complete loss of its capacity to compete with125I‐labelled hormone for rat‐liver binding sites, but modification of approximately half of the fast histidine group was enough to produce an important decrease in this capacity. Circular dichroism studies indicated no significant changes in protein conformation with all three histidine residues modified. Practically full binding capacity was restored when these residues were regenerated by treatment with hydroxylamine. These results suggest that one or both of the fast reacting histidine residues are involved in bovine growth hormone binding to its specific receptors.
Chemical modification of ribonuclease A with 4‐arsono‐2‐nitrofluorobenzene
Authors: HUMMEL HARLES F. , GERBER BERNARD R. , CARTY ROBERT P.
Published: August 2010

4‐Arsono‐2‐nitrofluorobenzene reacts selectively at the anion binding site of bovine pancreatic ribonuclease A. The major derivative is the inactive 41‐(4‐arsono‐2‐nitrophenyl) ribonuclease A (45% yield). Additional products are 1‐α‐(4‐arsono‐2‐nitrophenyl) ribonuclease A (11% yield) which is enzymatically active and the disubstituted, inactive 1,41‐bis‐(4‐arsono‐2‐nitrophenyl) ribonuclease A (25% yield). 2′ (3′)‐O‐Bromoacetyluridine reacts with 41‐(4‐arsono‐2‐nitrophenyl) ribonuclease A exclusively at the histidine‐12 residue at a rate which is approximately one‐fourth the rate observed with the unmodified enzyme. Saturation kinetics are observed and the dissociation constant for the protein‐inhibitor complex is 0.096 ± 0.023 M. The first‐order unimolecular decomposition constant for complex breakdown is 8.9 ± 2.9 times 10‐4s‐1. 2′‐Bromoacetamido‐2′‐deoxyuridine reacts with 41‐(4‐arsono‐2‐nitrophenyl) ribonuclease A 25 times more slowly than 2′(3′)‐O‐bromoacetyluridine. Bromo‐acetate reacts with 41‐(4‐arsono‐2‐nitrophenyl) ribonuclease A predominantly at the histidine‐119 residue at a rate 45 times less than that found for the unmodified enzyme. The results of the alkylation studies imply that the dianionic arsonate does not occupy the phosphate binding site in the enzyme but is sufficiently proximate to account for a decrease in bromoacetate binding as well as a reduction in the nucleophilic reactivity of histidine‐12 and ‐119. All these effects may be accounted for in terms of a local electrostatic perturbation of the active site region by the arsononitrophenyl group.
Structure and conformation of linear peptides
Authors: SUBRAMANIAN E. , LALITHA V. , BORDNER J.
Published: August 2010

L‐tyrosyl‐L‐tyrosine crystallizes as a dihydrate in the orthorhombic system, space group C2221, with a = 12.105(2), b = 12.789(2), c = 24.492(3) Å, Z = 8. The structure was solved by direct methods and refined to a final R‐value of 0.059 for 1740 observed reflections. The molecule exists as a zwitterion, the peptide unit is trans planar, and the backbone torsion angles correspond to an extended conformation, with e1 = 149.4°, e2 = ‐ 161.2°, e2 = 158.3°. The values of the side‐chain torsion angles (χ1, χ2) are (‐ 58.8°, ‐ 63.1°) for the first tyrosine and (‐ 171.7°, ‐ 116.5°) for the second. The planes of the aromatic rings are nearly parallel (dihedral angle of 6.1°), and their centers are separated by 10.9 Å. The carboxyl plane forms a dihedral angle of 23.8° with the plane of the peptide bond.
Ontogeny of the bovine neurohypophyseal hormone precursors
Authors: CHAUVET MARIE‐THÉRÈSE , CHAUVET JACQUELINE , ACHER ROGER
Published: August 2010

Neurohypophyseal hormones are fragments of precursor proteins that include specific neurophysins and are processed during axonal transport. Neurohormones and neurophysins purified from 7–9 month old bovine foetuses have been characterized by amino acid analysis and partial amino acid sequences. Oxytocin and arginine vasopressin, on one hand, and VLDV‐neurophysin and MSEL‐neurophysin, on the other, are identical to products previously characterized in the adult. Whereas oxytocin and vasopressin genes seem to be expressed at the same rates in the adult, as judged by the amounts of their peptide products in neurohypophysis, in the late foetus the vasopressin gene appears to be roughly three times more active than the oxytocin gene.
Isolation of large peptides derived by cyanogen bromide cleavage of thermolysin using fast protein liquid chromatography (FPLC)
Authors: VITA CLAUDIO , DALZOPPO DANIELE , PATTI SALVATORE , FONTANA ANGELO
Published: August 2010

The recently introduced fast protein liquid chromatography (FPLC) system of Pharmacia (Uppsala, Sweden) was employed to isolate rather large peptides derived from thermolysin by selective chemical fragmentation at methionine in positions 120 and 205 of the polypeptide chain of 316 amino acid residues. Thermolysin was cleaved under conditions of limited fragmentation in order to produce, besides fragments 1–120, 121–205 and 206–316, the overlapping fragments 1–205 and 121–316. These polypeptides were separated employing prepacked Mono Q or Mono S columns (quaternary ammonium and sulfonic acid support, respectively). The columns were equilibrated with acetate‐7 M urea buffer, pH 5.0 or 6.0, and eluted with a gradient of sodium chloride or acetate. Separations were achieved in 10–20 min and were carried out also at a semipreparative level (1–3 mg per run). All five protein fragments were isolated in homogeneous form, as judged by amino acid analysis and electrophoresis. Considering that protein fragmentation with cyanogen bromide is the most commonly used procedure to achieve selective chemical fragmentation of a polypeptide chain, these results indicate that FPLC with ionic exchangers can be usefully employed to isolate rather large protein fragments especially suitable for automatic sequence analysis with the sequenator.
Brain and pituitary β‐endorphin levels at different developmental stages of the rat
Authors: NG TZI BUN , HO WALTER K.K. , TAM PATRICK P.L.
Published: August 2010

β‐Endorphin‐like immunoreactivity in whole brains of Sprague‐Dawley rat fetuses of different gestational ages was measured by radioimmunoassay and found to increase throughout the gestational period studied. The immunoreactivity in various brain parts (forebrain, midbrain, hindbrain, hypothalamus and pituitary) of late prenatal, early postnatal, young mature and retired breeder rats was also determined. In all the brain parts studied, a maximum in the content and concentration of β‐endorphin‐like immunoreactivity was attained when the rats were about 3–4 months old.
Racemization mechanism of serine dipeptide active ester derivatives*
Authors: KOVACS J. , JHAM G.N. , HUI K.Y. , HOLLERAN E.M. , KIM S.E. , CANAVAN T.
Published: August 2010

The racemization of Z‐Gly‐Ser(Bzl)‐OPcp was studied using the isotope effect to distinguish between enolization and 5(4H)‐oxazolone mechanism. Labeled Z‐Gly‐L(α2H)‐Ser(Bzl)‐OPcp was racemized with NEt3 in THF to give kr2H = 570; similarly the unlabeled Z‐Gly‐L‐Ser(Bzl)‐OPcp yielded a racemization rate constant of krH = 720. The krH/kr2H ratio of 1.3 indicates that the serine dipeptide active ester derivatives racemize mainly through 5(4H)‐oxazolone and to a lesser extent through the enolization mechanism, provided the 5(4H)‐oxazolone racemizes much faster than it couples. 5(4H)‐Oxazolone was prepared from Z‐Gly‐L‐Ser(Bzl)‐OH with DCC. Its first order racemization rate constant in THF is independent of its concentration, indicating that the racemization is not an intermolecular autoracemization. The unimolecular, that is intramolecular self‐catalyzed, racemization is not possible based on molecular models. Therefore, it must be a solvent catalyzed bimolecular reaction. Its racemization was instantaneous with NEt3 while its coupling with H‐Val‐OMe was found to be 4 times 10‐2M‐1 s‐1, that is kr± kc. The kc/kr values, which indicate the extent of racemization during coupling, are compared for benzyloxycarbonylamino and benzyloxycarbonylglycylamino acid active esters; the most vulnerable amino acids are His, Cys and Ser. The kc/kr values also indicate that for practical synthetic purposes the pentafluorophenyl esters should be preferred over other active esters to minimize racemization.
N.m.r. studies of myelin basic protein
Authors: MENDZ GEORGE L. , MOORE WALTER J. , KING GARRY , WRIGHT PETER E.
Published: August 2010

The peptide Phe‐Lys‐Leu‐Gly‐Gly‐Arg‐Asp‐Ser‐Arg derived from myelin basic protein is part of an epitope encephalitogenic in rhesus monkey and cross reactive with certain tumor antigens. Its proton n.m.r. spectrum has been studied in dimethyl‐sulfoxide solutions over a range of temperatures. Following assignment of all the resonances by standard one‐ and two‐dimensional n.m.r. methods, nuclear Overhauser and chemical‐shift data indicate that the molecule has considerable mobility about the central pair of Gly‐Gly residues, an electrostatic or hydrogen bond between the sidechains of Asp7 and Arg9, and other nonrandom structures in the N‐ and C‐terminal portions.
Backbone conformations, bend structures, helix structures and other tests of an improved conformational energy program for peptides: ECEPP83
Authors: CHUMAN H. , MOMANY F.A. , SCHÄFER L.
Published: August 2010

Improvements in the potentials used in the computer program ECEPP (empirical conformational energy program for peptides) and a variety of test cases using a new program (ECEPP83) are described. The changes made in ECEPP are based on recent results of ab initio geometry optimized dipeptide studies, and also on the inability of ECEPP potentials to predict low‐energy conformations in regions of Ø‐Ø space where experimental β‐bends occur. The concept of the thermal ellipsoid is also developed as a method for visualizing correlated conformational motion about energy minima. A series of previously studied bend structures in proteins are examined again using the improved program, ECEPP83. The changes made to the program are found to result in significant modifications in the ordering of computed energy minima, protein bend structures, and in the values of Ø and Ø at the energy minimum for helical homopolymers. Agreement with experiment is improved over that found using ECEPP.
Tyrosine residues of bovine thyrotropin
Authors: STRICKLAND THOMAS W. , WILLIAMS JEFFREY F. , PIERCE JOHN G.
Published: August 2010

The susceptibility of the tyrosines of bovine thyrotropin (bTSH) and of its isolated α and β subunits to lactoperoxidase catalyzed iodination was examined as a probe of the reactivity of these residues. In isolated TSHα, tyrosines at positions 21, 41, 92 and 93 were labeled with radioactive iodine to a nearly equivalent extent while residue 30 did not incorporate iodine. In intact TSH tyrosine 41, as well as 30, was not modified showing that, upon association with β subunit, residue 41 becomes substantially less reactive. The other three tyrosines of the α subunit retained reactivity; residue 21 incorporated relatively more label than residues 92 and 93. The pattern of reactivity of the TSHα tyrosines in intact TSH parallels previous studies on the α subunits of lutropin (LH) and human choriogonadotropin (hCG). Thus the different primary sequences of the β subunits do not influence environments around tyrosines at positions which are spaced throughout the α subunit structure. Most of the 11 tyrosine residues of TSHβ incorporate significant amounts of iodine. In intact TSH, β tyrosines 25, 37, and 119 are most readily iodinated and tyrosines 14, 25 and 37 are the most reactive in the isolated subunit. Of particular interest in intact TSH is that tyrosine 37 and to a lesser extent 61 are modified. These tyrosines are found in analogous and highly conserved domains in the β subunits of all glycoprotein hormones whose sequences have been determined, but in LH and hCG they can only be iodinated in isolated β subunits.
Intramolecular sulfhydryl‐catalyzed structural alteration of bovine plasma albumin–N‐A isomerization*
Authors: INOUYE HIROSHI , ERA SEIICHI , SAKATA SHIGEKI , KUWATA KAZUO , SOGAMI MASARU
Published: August 2010

The N‐A isomerization of bovine plasma albumin (BPA) (the intramolecular sulfhydryl‐disulfide exchange reaction) is not a two‐state but a multi‐state reaction as shown in the following equation

N ± A1 + mH+ ± A2 + nH+ ±

where N and A1 are the N‐ and A(aged)‐forms, respectively. The N‐A isomerization was strongly suppressed by increasing the ionic strength, especially by divalent cations, such as Ca2+. The N‐A isomerization was completely suppressed in the presence of 20 mM sodium caprylate and 40 mM N‐acetyltryptophan. This suppression of the intramolecular sulfhydryl‐disulfide exchange reaction might be due to the reduction of the structural fluctuation of BPA.
Origin of a fluorescence increase accompanying the limited proteolysis of fluorescein‐labeled human prothrombin by Factor Xa
Authors: MORRISON SIDONIE A.
Published: August 2010

In a search for a probe which would report its proteolysis to thrombin, the human blood coagulation zymogen prothrombin was covalently labeled with fluorescein. Fluorescein isothiocyanate (FITC) and dichlorotriazinylamino‐fluorescein (DCTAF) both introduced ˜ 1 molecule of dye, but labeling occurred at different locations, as FITC had no effect on clotting activity whereas DCTAF caused 95% inactivation. At pH 9.0 DCTAF, but not FITC, could induce labeling up to 4 mol/mol. All derivatives were activated normally by prothrombinase (the activating complex of Factor Xa, Factor V(a), Ca2+ and phospholipids), as indicated by the pattern of bands on SDS gel electrophoresis and an unaltered yield of activity toward a chromogenic substrate for thrombin. Upon undergoing this limited proteolysis, the most heavily labeled derivative showed a 40% increase in fluorescence of the fluorescein at 520 nm (Λex 480 nm). In contrast, the fluorescence of lightly labeled forms was more intense but increased by only 0–5% upon activation. The data suggest that the lower fluorescence of the most labeled form is due to an intramolecular quenching effect between the dye molecules on individual polypeptide chains that is partly relieved when activation occurs.
Cyclic peptides
Authors: KOZONO TOSHIRO , MIHARA HISAKAZU , AOYAGI HARUHIKO , KATO TETSUO , IZUMIYA NOBUO
Published: August 2010

In order to explore the route for cyclization of linear oligopeptide containing a ΔAla (α, β‐dehydroalanine) residue, AM‐toxin II was synthesized. As a preliminary experiment, synthesis of [L‐Phe3] AM‐toxin II, containing L‐Phe in place of L‐App (L‐2‐amino‐5‐phenylpentanoic acid), was attempted. Cyclization of H‐L‐Phe‐ΔAla‐L‐Ala‐L‐Hmb‐ONSu in pyridine at 3 mM concentration yielded a mixture of cyclic dimer and cyclic polymers. Cyclization of H‐L‐App‐ΔAla‐L‐Ala‐L‐Hmb‐ONSu under the same conditions gave similar results; however, cyclization at 0.3 mM concentration yielded a mixture of desired cyclic monomer and cyclic dimer. An appreciable amount of cyclic monomer was isolated from the mixture. Characteristic features of the monomer were identical to those of natural AM‐toxin II.
Conformational changes in cyclic (D‐Phe‐Pro‐Gly‐D‐Ala‐Pro) upon complexation with Mg++.
Authors: Karle Isabella L.
Published: August 2010

Upon long standing and very slow evaporation, a solution of the cyclic penta‐peptide and Mg(SCN)2 in CDCl3/CD3CN produced colorless crystals of a 1:1 complex of the peptide and Mg++. X‐ray diffraction analysis showed the contents of the asymmetric unit to be C24H31N5O5˙ Mg++˙ NCS‐˙ HSO‐4˙ 6H2O (P212121, a = 8.444 (1) A, b = 10.735 (2) A, c = 39.726 (6) A). This first example of a metal ion complex with a cyclic pentapeptide is in the form of an infinite stack with alternating peptide and Mg++ moieties. The octahedrally coordinated Mg++ makes only two ligands with the peptide carbonyls: O(3)—Mg++ above and O(1)—Mg++ below. The equatorial coordinations involve three H2O molecules and NCS‐. There is a profound change in conformation upon complexation, with several ø and ø values changing by 90° to 230°. One NCS‐ oxidizes to HSO‐4 to provide the counter‐ion.
Crystal structure of cyclo‐L‐histidyl‐L‐methionine and studies of metal complexation with divalent metal ions
Authors: Bressan M. , Marchiori F. , Valle G.
Published: August 2010

The structure of the title compound displays a buckled diketopiperazine ring. The two side‐chains are both folded, with the imidazole ring facing the methionine chain. Imidazole nitrogen is the primary site for metal coordination of the ligand. Only for copper (II) adducts and in the solid state are there evidences of additional coordination through the sulfur atom.
Backbone side chain interactions in peptides.
Authors: Aubry A. , Ghermani N. , Marraud M.
Published: August 2010

The preferential occurrence of amino‐acid residues having short polar side‐chain within β‐folded regions of crystallized proteins suggests the existence of some stabilizing interaction involving the side polar function. Three model dipeptides tBuCO‐l‐Pro‐l‐Ser‐NHMe 1, tBuCO‐l‐Pro‐d‐Ser‐NHMe 2 in the pure enantiomeric a and racemic b forms, and iPrCO‐l‐Pro‐d‐Ser‐OMe 3 have been investigated in the solid state by X‐ray crystallography. Homo and heterochiral sequences 1 and 2 are folded in the βI and βII types, respectively, whereas 3 obviously accommodates an open conformation. Besides the i + 3 →i hydrogen bond typical of β‐bends in 1, 2a, and 2b, the Ser NH group in all four crystal structures is a proton donor to the lone orbitals of the Ser Oγ oxygen atom. The result is that the disposition of the Ser Cα–Cβ bond corresponds to the rotamer III (χ1⋍ 60°). As shown by the crystal structure of 3, the intra‐Ser NH.Oγ hydrogen bonding is not restricted to β‐folded Pro‐Ser sequences. Therefore, this interaction is not only a stabilizing factor for β‐turns but it is also probably responsible for the already mentioned stability of rotamer III for the Ser Cα–Cβ bond in peptides and protein.
Synthesis and conformational study of a cyclic hexapeptide analog of somatostatin containing dehydrophenylalanine
Authors: Brady Stephen F. , Cochran David W. , Nutt Ruth F. , Holly Frederick W. , Bennett Carl D. , Paleveda William J. , Curley Paul E. , Arison Byron H. , Saperstein Richard , Veber Daniel F.
Published: August 2010

A cyclic hexapeptide analog of somatostatin, cyclo‐(Pro‐Δz‐Phe‐d‐Trp‐Lys‐Thr‐Phe) (II)† has been synthesized by a combination of solid phase and solution methodology. It shows a potency for inhibition of growth hormone release in vitro about one‐tenth that of the corresponding saturated analog, cyclo‐(Pro‐Phe‐d‐Trp‐Lys‐Thr‐Phe) (I). N.m.r. studies indicate comparable backbone conformations for analogs I and II. However, the sum of our findings from biological evaluation and solution physical data suggest that on the receptor the position‐7 phenyl ring of I is adopting a conformation which differs from that of one of the major solution conformers defined previously by n.m.r. studies.
Effects of structure‐forming solutes on chicken eggwhite lysozyme after reductive cleavage of disulfide bonds
Authors: White Frederick H. , Wright A. Gilbert
Published: August 2010

As an approach to learning more about structure‐forming processes in chicken eggwhite lysozyme, the reduced protein was studied in the presence of methanol, 2‐chloroethanol, trifluoroethanol, and sodium dodecyl sulfate, at various concentrations in aqueous solution. The mixtures were subjected to gel filtration chromatography, with circular dichroism (CD) examination of the resulting polymers and monomers. Changes in CD behavior, indicating development of ordered structure, were seen to be associated only with polymer formation. Contributing to these changes were increases in β structure as well as α‐helix. Since the solutes studied are known as helix formers, it is suggested that studies on many proteins, carried out in the presence of these and other structure‐modifying solutes, may have been complicated by formation of β structure as well as by polymerization. The reduced monomer formed no structure in the hydrophobic environment afforded by these solutes, but only randomized further. Thus, hydrophobic interactions may be of no significance to lysozyme chain folding in its early stages. As an alternative, the long range interactions stabilized by native tertiary cross links may be critical for the transition to native secondary structure.
Acceptors in the removal of protecting groups
Authors: Bodanszky Miklos , Bodanszky Agnes
Published: August 2010

Acidolytic cleavage of benzyloxycarbonyl and O‐benzyl groups with trifluoroacetic acid is accelerated by the addition of 4‐(methylmercapto)phenol (4MP) that can play the role of acceptor of benzyl groups in two different ways and can replace the previously used thioanisole‐m‐cresol mixture. Some advantages of 4MP are pointed out and its usefulness is demonstrated in practical examples.
Precursor polyproteins in endocrine and neuroendocrine systems
Authors: Chretien M. , Seidah N.G.
Published: August 2010

The biosynthesis of neuro and hormonal peptides is in a state of rapid progress. The development of protein microsequencing is making it possible to characterize more and more new important molecules with nanomolar quantities, while the DNA structural studies favor the sequencing of the precursors of all these new peptides. These precursors are often polyproteins containing more than one active end‐product. Their maturation processes are following a highly similar pattern with cleavage of the precursors at sites characterized by the presence of pairs of basic amino acid as noted in 1967–68 for the LPH and the pro‐insulin models. This now constitutes a general concept which has good chances to be applicable to all the exciting neuro and hormonal peptides recently identified or yet to be discovered.
Application of N,N‐dimethylformamide dineopentyl acetal for efficient anchoring of Nα‐9‐fluorenylmethyloxycarbonylamino‐acids as p‐alkoxybenzyl esters in solid‐phase peptide synthesis
Authors: Albericio Fernando , Barany George
Published: August 2010

The attachment of Fmoc‐amino acids onto p‐alkoxybenzyl alcohol resins via DCC‐DMAP coupling suffers from two different problems: formation of dimers and racemization. The use of N,N‐dimethylformamide dineopentyl acetal for the preparation of Fmoc‐aminoacyloxybenzyl handles is the basis of a safe and efficient anchoring method that avoids both problems.
4‐Sulfobenzyl ester – its use in peptide synthesis
Authors: Bindewald Roland , Danho Waleed , BüLlesbach Erika E. , Bodanszky Miklos , Zahn Helmut
Published: August 2010

Amino acid 4‐sulfobenzyl esters were employed for the synthesis of peptides in solution. They significantly increase the hydrophilicity of protected intermediates as shown by analytical reversed‐phase high performance liquid chromatography and counter‐current distribution. General methods for working up are described which permit simple and standardized isolations of products. The use of several coupling methods was demonstrated in the synthesis of Z‐Val‐Gly‐OBzl‐SO3NH4. Ion‐exchange chromatography was introduced as a selective purification procedure for protected peptide 4‐sulfobenzyl esters. A step‐wise synthesis of [Leu5]‐enkephalin was performed, starting from leucine 4‐sulfobenzyl ester. Removal of N‐terminal protecting groups produced zwitterionic peptide 4‐sulfobenzyl esters. These were readily purified by crystallization from slightly acidic media; no further purification was necessary. The biologically fully active pentapeptide Tyr‐Gly‐Gly‐Phe‐Leu was obtained in an overall yield of 30.2%.
Preparation of a specifically tritiated locust adipokinetic hormone analog with full biological potency
Authors: Muramoto Koji , Ramachandran J. , Moshitzky Pnina , Applebaum S.W.
Published: August 2010

A synthetic peptide related to locus adipokinetic hormone (AKH) and shrimp red pigment concentrating hormone (RPCH) containing a tyrosine residue in place of phenylalanine was iodinated and the 3,5‐diiodotyrosyl derivative was isolated by reverse phase HPLC. Catalytic dehalogenation of the diiodo derivative in the presence of tritium yielded the tritiated AKH analog which was isolated by gel filtration on Sephadex LH‐20 and reverse phase HPLC. The tritiated peptide was formed to be identical to AKH in its ability to stimulate lipid release into the hemolymph of locusts in vivo where the diiodotryrosyl derivative was inactive. The specific radioactivity of the tritiated peptide was 57.2 Ci/mmol, or 99% of the theoretical value.