摘要:

The data obtained in the earlier parts of this series for the donor and acceptor end parameters of N‐H. O and O‐H. O hydrogen bonds have been utilised to obtain a qualitative working criterion to classify the hydrogen bonds into three categories: “very good” (VG), “moderately good” (MG) and weak (W). The general distribution curves for all the four parameters are found to be nearly of the Gaussian type. Assuming that the VG hydrogen bonds lie between 0 and ± la, MG hydrogen bonds between ± 1s̀ and ± 2s̀, W hydrogen bonds beyond ± 2s̀ (where s̀ is the standard deviation), suitable cut‐off limits for classifying the hydrogen bonds in the three categories have been derived. These limits are used to get VG and MG ranges for the four parameters1and θ (at the donor end) and ± and ± (at the acceptor end). The qualitative strength of a hydrogen bond is decided by the cumulative application of the criteria to all the four parameters. The criterion has been further applied to some practical examples in conformational studies such as α‐helix and can be used for obtaining suitable location of hydrogen atoms to form good hydrogen bonds. An empirical approach to the energy of hydrogen bonds in the three categor

ISSN:0367-8377    

DOI:10.1111/j.1399-3011.1981.tb02007.x

出版商:Blackwell Publishing Ltd    

年代:1981

数据来源: WILEY

摘要:

The optical rotatory features of the β‐structure of the polypeptides in nonaqueous solutions and films cast from these solutions have been investigated. The β‐structure of poly‐S‐benzyl‐L‐cysteine, poly‐S‐carbobenzoxy‐L‐cysteine and poly‐S‐benzyl‐L‐cysteine, poly‐S‐carbobenzoxy‐L‐cysteine and poly‐O‐carbo‐bands of their films. The optical rotatory dispersion (ORD) and circular dichroism (CD) spectra of these polypeptides are found to be very similar in both film and solution. In solvents promoting the β‐structure, the polypeptides are characterized by CD troughs in the n‐±* transition region of the peptide chromophore. The ORD spectra are found to be positive in sign throughout the visible and accessible ultraviolet regions and are interpreted in terms of the possible existence of a relatively much larger positive π‐π* CD band as compared with the negative π‐π* band. The rotatory data obtained in the non‐aqueous solution are compared with those obtained for other poly peptides in aqueous solutions,

ISSN:0367-8377    

DOI:10.1111/j.1399-3011.1981.tb02008.x

出版商:Blackwell Publishing Ltd    

年代:1981

数据来源: WILEY

摘要:

The specific side‐chain orientations of the phenyl group in the polypeptides poly‐S‐benzyl‐l‐cysteine, poly‐S‐carbobenzoxy‐l‐cysteine and poly‐O‐carbobenzoxy‐l‐serine in the β‐structure have been studied by spectral measurements in solution. All the three polypeptides exhibit aromatic CD bands, indicating the asymmetric placement of the side‐chain phenyl rings when the polypeptide backbone takes up the antiparallel β‐structure. Supporting evidence for this is derived from n.m.r. spectra of the polypeptides, which show up field shift of the phenyl protons due to the stacking of the aromatic rings. Molecular model building studies reveal the stacking of alternate phenyl g

ISSN:0367-8377    

DOI:10.1111/j.1399-3011.1981.tb02009.x

出版商:Blackwell Publishing Ltd    

年代:1981

数据来源: WILEY

摘要:

Insulin performic acid‐oxidized A chain was digested with subtilisin type Carlsberg. The kinetics of proteolysis was studied and the bonds split with fast and with slow reactions were identified. The most susceptible bonds are CySO3H 11‐Ser 12 and Leu 13‐Tyr 14. Three bonds are hydrolyzed at a slower rate: Leu 16‐Glu 17, Asn 18‐Tyr 19 and Tyr 19

ISSN:0367-8377    

DOI:10.1111/j.1399-3011.1981.tb02010.x

出版商:Blackwell Publishing Ltd    

年代:1981

数据来源: WILEY

摘要:

Structure‐function and conformational studies of the molecule of phagocytosis‐stimulating tetrapeptide tuftsin permitted the conclusion that among products resulting from splitting of H‐chain of IgG Human EU by trypsin, besides tuftsin (sequence 289–292), tuftsin‐like tetrapeptide Gly‐Gln‐Pro‐Arg may be also present; theoretical conformational analysis shows a considerable similarity of spatial arrangement of this tetrapeptide and tuftsin which testifies in favour of potential tuftsin‐like activity of the tetrapeptide. Gly‐Gln‐Pro‐Arg was synthesized and its phagocytosis stimulating activity was found e

ISSN:0367-8377    

DOI:10.1111/j.1399-3011.1981.tb02011.x

出版商:Blackwell Publishing Ltd    

年代:1981

数据来源: WILEY

摘要:

A computer program was designed for determining candidate sequences of polypeptides and proteins from the molecular weights andN‐terminal partial sequences of the peptide fragments derived from the polypeptides and proteins by specific cleavages. The basic principle for sequencing a protein by this method is describe

ISSN:0367-8377    

DOI:10.1111/j.1399-3011.1981.tb02012.x

出版商:Blackwell Publishing Ltd    

年代:1981

数据来源: WILEY

摘要:

The hormone analog 8‐l‐tryptophan‐oxytocin was synthesized in solution by stepwise chain lengthening from theC‐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‐Trp8distance 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 13.5Åbetween the side chains of tyrosine and tryptophan measured in aqueous solution is compatible with the Tyr2‐Leu8distance determined with molecular models built according to the proposals of Walter for the biologically active

ISSN:0367-8377    

DOI:10.1111/j.1399-3011.1981.tb02013.x

出版商:Blackwell Publishing Ltd    

年代:1981

数据来源: WILEY

摘要:

The presence of secondary structure and the strong conformational resistance of porcine pancreatic trypsin inhibitors (Kazal inhibitors) PSTI I and PSTI II to denaturant agents have been investigated by circular dichroism (CD) and fluorescence measurements. These proteins heated for 6 h at 85° are still highly active

ISSN:0367-8377    

DOI:10.1111/j.1399-3011.1981.tb02014.x

出版商:Blackwell Publishing Ltd    

年代:1981

数据来源: WILEY

摘要:

Thermal perturbation (TP) spectra of luliberin were measured at pH 5–8, and compared with the model chromophoresN‐Ac‐Tyr‐NH2,N‐Ac‐Trp‐NH2, t‐Boc‐His‐Trp‐NH2, H‐His‐Trp‐OH, Ac‐His‐Trp‐OH, tryptophan andcyclo‐ [His‐Trp] (alll‐isomers). Between pH 5 and neutrality, the major TP extremum of the Trp3residue of luliberin increases by about 50%. A similar effect is seen for luliberin acetylated on Tyr5. The effect with luliberin is attributed to the protonation of the His2residue. One proposed explanation is that the protonated imidazole orients water around the nearby indole in a different way than does unprotonated imidazole. The Tyr5residue of luliberin behaves likeN‐Ac‐Tyr‐NH2, and is considered to be well exposed to solvent. The TP spectra ofN‐Ac‐Trp‐NH2, t‐Boc‐His‐Trp‐NH2, Ac‐His‐Trp‐OH, andcyclo‐[His‐Trp] are pH‐independent from pH 5 to 8. The TP spectrum ofH‐His‐Trp‐NH2has a bell‐shaped pH dependence, rising from normal at pH 3.5 to above normal at pH 6, and returning to normal at pH 8. Luliberin and model peptides show that

ISSN:0367-8377    

DOI:10.1111/j.1399-3011.1981.tb02015.x

出版商:Blackwell Publishing Ltd    

年代:1981

数据来源: WILEY

摘要:

The study oftBuCO‐l‐Pro‐Me‐l‐Ala‐NHiPr (1) by i.r. and n.m.r. spectroscopies has indicated that the middle amide group accommodates preferentially thecisarrangement in inert (CCl4) and aprotic (DMSO) solvents.Cisconformers are folded by a strong intramolecular hydrogen bond involving both terminal CO and NH groups whereas the minortransconformers accommodate an open conformation. Thecisfolded form is retained in the solid state and its crystal structure was fully characterized by X‐ra

ISSN:0367-8377    

DOI:10.1111/j.1399-3011.1981.tb02016.x

出版商:Blackwell Publishing Ltd    

年代:1981

数据来源: WILEY