摘要:

The dependence of the13C shift difference of proline carbons Cβand Cγon the dihedral angle ø has been studied using the model peptide acetyl‐d‐proline N‐methylamide. The shift difference Δβγis shown to be correlated with the percent cis isomer about the acetylproline bond, both factors depending strongly on the degree of intermolecular hydrogen bonding. Both the fraction of trans peptide bond and the fractional γ‐turn conformation increase as the sample concentration is decreased in CDCl3. Δβγvalues have been used to evaluate the fractional γ‐turn probabilities in a number of cyclic and linear peptides including thyrotropin releasing factor and bradykinin. Using this parameter, it is concluded that in bradykinin the γ‐turn probability is low in D2O and not strongly temperature dependent. In contrast, studies of a model peptide for the portion of bradykinin believed to adopt a γ‐turn conformation are consistent with an increased γ‐turn probability in less polar solvents. Data for X‐Pro‐Y peptides (Y = imino acid) indicate significantly reduced values of Δβγ, and this appears to be a useful basis for assigning the Pro Cβreso

ISSN:0367-8377    

DOI:10.1111/j.1399-3011.1979.tb01948.x

出版商:Blackwell Publishing Ltd    

年代:1979

数据来源: WILEY

摘要:

Analysis of the effect of temperature on the circular dichroism spectrum of bradykinin has led to a more precise understanding of the solution conformation of the peptide. Circular dichroism and13C n.m.r. have been used in a complementary fashion to support the picture that bradykinin spends a maximum of about 20% of its time in a partially ordered conformation featuring a γ‐turn with Pro7as the second residue. Since the γ‐turn probability is insensitive to temperature, some other conformational effect dominated by the structure of water presumably produces the pronounced change in the circular dichroism spectrum with increasing temper

ISSN:0367-8377    

DOI:10.1111/j.1399-3011.1979.tb01949.x

出版商:Blackwell Publishing Ltd    

年代:1979

数据来源: WILEY

摘要:

Ion‐exchange derivatives are described, of a hydrophilic rigid macroporous glycolmethacrylate gel called Spheron, suitable for rapid high‐performance liquid chromatography (HPLC) of proteins and their fragments. Their flow parameters are compared with those of ion exchange derivatives of cellulose and poly‐dextran. The conditions for work with them are described (regeneration, cycling, equilibration, column packing) as well as the construction of a simple apparatus for medium‐pressure ion exchange chromatography of proteins. The efficiency of these ion exchangers for the separation of proteins is illustrated with examples of chromatography of an artificial mixture of serum albumin, chymotrypsinogen and lysozyme. Chromatography of cyanogen bromide fragments of serum albumin and the A and B chains of oxidized insulin showed that the method can be applied in chromatography on higher molecular protein fragments. A review of all proteins, including technical enzymes, which have already been chromatographed on Spheron ion exchangers is also given. The prospects of Spheron ion exchangers for HPLC of proteins and their fragments are briefly di

ISSN:0367-8377    

DOI:10.1111/j.1399-3011.1979.tb01950.x

出版商:Blackwell Publishing Ltd    

年代:1979

数据来源: WILEY

摘要:

The optimized energies of seven β‐bends, repeating C5 and C7, and right‐ and left‐handed α‐helical conformations for each of eight tetrapeptides have been computed using empirical methods. Eight tetramers were selected: four helix‐forming sequences with hydrophobic residues such as Val, Leu, Ile and Trp, and four helix‐breaking sequences with hydrophilic residues such as Asp, Asn and Ser, as determined by their frequency of occurrence in beta turns in proteins. Analysis of the optimized conformations with energies ≤2.1 kcal/mol from the absolute minimum energy conformer for each tetramer reveals a correlation between low‐energy conformations and those predicted from observed protein structures. These results show that energy calculations on small peptide fragments may be useful in predicting

ISSN:0367-8377    

DOI:10.1111/j.1399-3011.1979.tb01951.x

出版商:Blackwell Publishing Ltd    

年代:1979

数据来源: WILEY

摘要:

Preparations of thiol:protein disulfide oxidoreductase from bovine liver were shown to be homogeneous by polyacrylamide gel electrophoresis, sedimentation equilibrium centrifugation and NH2‐terminal analysis (Carmichael et al., 1977). When the enzyme was subjected to prolonged storage at ‐20°, freeze‐thawing, or heating at 60°, at least one new protein species was observed using polyacrylamide gel electrophoresis. The new protein results from dimerization of the enzyme. The dimer consisted of two monomers held together by an inter‐molecular disulfide bond. The formation of this dimer can be reversed and partially prevented

ISSN:0367-8377    

DOI:10.1111/j.1399-3011.1979.tb01952.x

出版商:Blackwell Publishing Ltd    

年代:1979

数据来源: WILEY

摘要:

Detailed analyses of the conformations of the homo‐oligopeptide series, Boc‐(L‐Met)n‐OMen =2–7, in deuterochloroform have been carried out with proton n.m.r. and IR spectroscopy. Well‐resolved high field n.m.r. spectra with assignments for the NH and α‐CH resonances of these homo‐methionine peptides are presented. Extensive n.m.r. concentration‐dependent chemical shift studies are combined with IR results to delineate the involvement of the various methionine NH protons in intra‐ and/or intermolecular hydrogen bonding. N.m.r. chemical shift dependencies with temperature and solvent, DMSO‐d6,are used to explore the strength of the hydrogen bonds for the various oligopeptides. At low concentrations, where peptide aggregation is absent, the dipeptide is found to be disordered. The tetra‐ to heptapeptides possess intramolecular hydrogen bonded seven‐membered rings at internal residues. The number of internal rings and the oligopeptide self‐association increase with increasing peptide chainlength. At intermediate concentrations associations of peptide molecules with folded structures occur with initial association at theC‐terminal region. At high concentrations, “in‐register” associa

ISSN:0367-8377    

DOI:10.1111/j.1399-3011.1979.tb01953.x

出版商:Blackwell Publishing Ltd    

年代:1979

数据来源: WILEY

摘要:

We report the synthesis of nine lipophilic derivatives of N‐acetyl‐muramyl‐l‐alanyl‐d‐glutamic‐α‐amide (MDP) or ‐α‐methyl ester in which the γ‐carboxyl function of thed‐glutamyl residue is either esterified by a medium chain alcohol or substituted by anl‐alanyl residue esterified by a medium or long chain alcohol. A new method is described which easily allows one to obtain derivatives of MDP, bearing a free or substituted amino‐acyl or peptidyl resi

ISSN:0367-8377    

DOI:10.1111/j.1399-3011.1979.tb01954.x

出版商:Blackwell Publishing Ltd    

年代:1979

数据来源: WILEY

摘要:

Racemictrans, trans‐3,4‐dideutero proline has been prepared by catalytic deuteration of 3‐pyrroline‐2‐carboxylic acid. The stereospecificity of the reduction (i.e.transto the carboxylic group) was ascertained after transformation of the dideutero compound into the diketopiperazide c/Pro, Aib/, for which unambiguous proton assignments in the1H n.m.r. spectrum had been obtained previously. The identification of the configuration of the dideutero‐proline allows for the affirmation of the correctness of proton assignments as previously proposed in

ISSN:0367-8377    

DOI:10.1111/j.1399-3011.1979.tb01955.x

出版商:Blackwell Publishing Ltd    

年代:1979

数据来源: WILEY

摘要:

The amino groups of ovomucoid, lysozyme and ovotransferrin have been extensively alkylated by reacting the proteins with various carbonyl reagents in the presence of sodium borohydride. The extent of modification ranged from 40 to 100%. Essentially monosubstitution was obtained with acetone, cyclopentanone, cyclohexanone and benzaldehyde, while 20–50% disubstitution was obtained withN‐butanal and nearly 100% disubstitution was obtained with formaldehyde. Both the methylated and isopropylated derivatives of all three proteins were soluble and retained almost full biochemical activities, but introduction of the larger substituents caused precipitation with lysozyme and ovotransfer

ISSN:0367-8377    

DOI:10.1111/j.1399-3011.1979.tb01956.x

出版商:Blackwell Publishing Ltd    

年代:1979

数据来源: WILEY

摘要:

Two analogs of bovine insulin, [des(tetrapeptide B27–30),Tyr(NH2)26‐B] and [des(pentapeptide B26–30),Phe(NH2)25‐B] insulin, which differ from the parent molecule in that the C‐terminal tetrapeptide and pentapeptide sequences, respectively, from the B chain have been eliminated and the newly exposed residues are amidated, have been synthesized. The [des(tetrapeptide B27–30),Tyr(NH2)26‐B] insulin shows potencies of 16.8 IU/mg by the mouse convulsion assay method and 10.8 IU/mg by the radioimmunoassay method. The [des(pentapeptide B26–30), Phe(NH2)25‐B] insulin possesses a potency of 10.5 IU/mg when assayed by the mouse convulsion method and 14 IU/mg by the radioimmunoassay technique. The potencies of these analogs are higher than the potencies of the respective non‐amidated derivatives (Katsoyanniset al.,1973, 1974). It is speculated that the gradual decline of biological activity observed as amino acid residues are eliminated from theC‐terminal region of the B chain of insulin is due to the proximity of a hydrophilic carboxyl group to the hydrophobic core of

ISSN:0367-8377    

DOI:10.1111/j.1399-3011.1979.tb01957.x

出版商:Blackwell Publishing Ltd    

年代:1979

数据来源: WILEY