摘要:

The1H and13C n.m.r. spectral parameters of CTP‐NH2[d‐Phe‐Cys‐Tyr‐d‐Trp‐Lys‐Thr‐Pen‐Thr‐NH2], a potent, highly selective μ‐opiate antagonist, were measured in aqueous solution and a possible conformation has been deduced from the spectral data. The data are consistent with a type II'β‐turn for the tetrapeptide sequence ‐Tyr3‐d‐Trp4‐Lys5‐Thr6‐. Solvent shielding of the Cys2amide proton, observed in variable temperature experiments, suggests an orientation of this amide proton toward the gem dimethyls of Pen7with possible hydrogen bonding to the Thr6carbonyl oxygen, and a dihedral angle of −110° for the disulfide bond. Partially relaxed Fourier transform13C relaxation studies confirm a constrained cyclic system, with the Cα carbons in the “hinge” of the β‐turn having the shortest t1times. Segmen

ISSN:0367-8377    

DOI:10.1111/j.1399-3011.1988.tb00012.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY

摘要:

The tripeptides Z‐Pro‐Leu‐Gly‐OEt, Z‐Pro‐Leu‐Gly‐NH2and Z‐Pro‐Leu‐Gly‐OBzl were synthesized by thermolysin and α‐chymotrypsin catalysis. The optimum conditions for the couplings between Z‐Pro‐OH and H‐Leu‐OEt or H‐Leu‐Gly‐OEt catalysed by thermolysin were determined by a systematic study involving analysis of pH effect, ammonium sulfate concentration, reaction time, enzyme concentration, and relative proportion of the carboxyl and amine components. The best yield obtained for Z‐Pro‐Leu‐OEt was 77% and for Z‐Pro‐Leu‐Gly‐OEt, 100%. Z‐Pro‐Leu‐OEt was coupled to H‐Gly‐OEt, H‐Gly‐NH2and H‐Gly‐OBzl. The best conditions to obtain Z‐Pro‐Leu‐Gly‐OEt and Z‐Pro‐Leu‐Gly‐NH2were determined by the study of some factors that affect the reaction yield, such as organic solvent presence, substrate ratio and aqueous and organic solvent ratio. The yield obtained under optimum synthesis conditions was 55% for Z‐Pro‐

ISSN:0367-8377    

DOI:10.1111/j.1399-3011.1988.tb00013.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY

摘要:

Amino acid analyses after acid hydrolysis have demonstrated that luciferin, the substrate of the bioluminescent reaction of the dinoflagellatePyrocystis lunulaand its precursor. P630, possess the same peptide moiety. The molecular weight of the resulting chromopeptides would be 5400.

ISSN:0367-8377    

DOI:10.1111/j.1399-3011.1988.tb00014.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY

摘要:

A single crystal of17O enriched α‐glycine was grown by slow evaporation of aqueous solution.17O n.m.r. studies of the α‐glycine molecule in single crystalline form revealed five17O transitions each consisting of two lines due to inequivalency of the oxygen atoms in the unit cell, with each of these lines revealing a dipolar interaction between the17O and the nearest hydrogen atom. The spectral width was found to be of the order of magnitude of MHz and the linewidths of the order of magnitude of

ISSN:0367-8377    

DOI:10.1111/j.1399-3011.1988.tb00015.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY

摘要:

The effect of calcium (II) and magnesium (II) ions on the conformation of the 18–23 cyclic peptide loop of bovine prothrombin are investigated by the molecular mechanics program AMBER (Assisted Model Building with Energy Refinement). The work is an extension of an earlier paper (Eastmanet al, Int. J. Peptide Protein Res.27, 1986, 530–553) that employed the program ECEPP (Empirical Conformational Energy Program for Peptides). In the absence of either metal ion, or in the presence of either one Ca(II) or one Mg(II) ion, the lowest‐energy forms found by AMBER have the Gla21‐Pro22 peptide bond in atransconformation. In the presence of two Ca(II) or Mg(II) ions, the loop form of lowest energy is decidedlycis.The coordination about the Ca(II) and Mg(II) ions is different in both the single and double metal cases. In addition, the peptide chains that emerge from the loop are oriented parallel to each other in the lowest‐energy complex with two Ca(II) ions, but are not parallel in the lowest‐energy complex with two

ISSN:0367-8377    

DOI:10.1111/j.1399-3011.1988.tb00016.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY

摘要:

The gonadotropin of silver carp (scGTH) was purified from the pituitary glands in a yield of 8.4 mg g through extraction with 6% ammonium acetate (pH 5.1)–40% ethanol followed by 80% ethanol precipitation. DEAE‐cellulose chromatography and gel filtration. The molecular weight of scGTH is about 32 000 as estimated by gel filtration. Leucine and serine were the twoN‐termini of scGTH. The amino acid composition of scGTH is rich in aspartic acid asparagine, glutamic acid/glutamine, valine, proline and half cystine. Its carbohydrate content is 22.2%. Biologically, scGTH significantly stimulated the steroidogenesis in carp testis and ovaryin vitroand induced the ovulation in loaches. It also stimulated the32P‐phosphate uptake into 1‐day‐old chicken testis. Immunologically. scGTH could cross‐react with the anti‐serum against cGTH and vice versa. In both cases parallel displacement curves

ISSN:0367-8377    

DOI:10.1111/j.1399-3011.1988.tb00017.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY

摘要:

Previous potential energy calculations have always indicated that the folded conformation is the most stable one for cyclic dipeptides containing benzylic side chains. We have carried out intramolecular van der Waals potential energy calculations on cyclo‐(d‐Phe‐l‐Pro),N‐(N‐phenylacetyl‐l‐alanyl)‐cyclo‐(l‐Phe‐d‐Pro) andN‐(pyruvoyl)‐cyclo‐(l‐Phe‐d‐Pro) adopting the geometries found in their crystal structures. The calculations made on these compounds, having the peptide skeleton made of the same aminoacid residues but differing in the degree of buckling of the boat, show that there is a dependence between diketopiperazine ring and phenylalanine side‐chain conformations. The folded conformer is preferred as long as it is allowed by the degree of buckling of the boat. When the boat becomes highly buckled, as in the case of the pyruvoyl derivative, the folded rotamer is no longer favoured. This is the first energy calculation to demonstrate that the folded ro

ISSN:0367-8377    

DOI:10.1111/j.1399-3011.1988.tb00018.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY

摘要:

Crystal and molecular structures for the heterochiral sequenceN‐formyl‐l‐methionine‐d‐phenylalanine, 1, and its tertiary butyl ester, 2, are reported. The solid‐state peptide conformation is compared to that observed in solution by n.m.r. techniques. ForN‐f‐Met‐d‐Phe, 1, the crystal was orthorhombic, space group P212121with a cell of dimensions a = 5.061(3), b = 16.575(5) and c = 19.656(6) Å at ambient temperature of 293K; V = 1649(2)Å3, Z = 4, Dm= 1.31(2)gcm−3, Dx= 1.307gcm−3, μ(Mokx) = 2.047cm−1. ForN‐f‐Met‐d‐Phe‐OtBu. 2, the crystal was monoclinic, space group P21with a cell of dimensions a = 9.963(2), b = 11.147(2), c = 19.166(3)Å. β= 102.31(1) at 273K; V = 2080(2) Å3Z = 4, Dm= 1.22(2)gcm−3, Dx= 1.215gcm−3μ(MoKx) = 1.714cm−1. The structures were solved from diffractometer data and refined to conventional final R = 0.046, Rw= 0.053 for F‐Met‐d‐Phe (1301 observations. I ≥ 3σ(I)) and to R = 0.056, Rw= 0.064 for the t‐butylester (2411 observations. I ≥ 3σ(I)). Thel‐dacid, 1, crystallizes in an extended β‐sheet conformation withtrans‐planarpeptide bond; the principal torsion angle values are φ1=– 141.2(4).Ψ1= 149.6(4)3, φ2= 157.4(4)°. The methionine side chain adopts a common coiled conformation with x11= ‐ 58.0(5).x21= 175.1(4), x31= 76.5(5). The Phe side chain adopts the statistically least favored g orientation in contrast to the most populated rotamer in solution. The crystal structure is composed of parallel β‐sheets held together by four weak intermolecular contacts including two C‐H O contacts from the alpha carbons to the formyl and peptide carbonyl oxygens. Sheet layers are joined in a head‐to‐tail fashion through a very short (2.569(4) Å) contact between the carboxyl OH and the formyl oxygen and may be further stabilized by a C‐H—O interaction between the formyl proton and the carboxyl OH. Two crystallographically independent molecules are observed in the crystal structure ofN‐f‐l‐Met‐d‐Phe‐OtBu, 2. These are distinct conformational isomers differing principally at both theNandCtermini. Particularly noteworthy is the synplanar orientation of the ester C = O with respect to the peptide nitrogen in molecule A. which contrasts to the antiplanar orientation in molecule B. Additionally, the formyl group is coiled more towards theC‐terminus in molecule B. Principal torsion angles are φ1(A) = ‐ 120.6(5), Ψ1(A) = 102.0(6)°, φ2(A) = 128.1(6), φ1(B) = ‐ 94.6(5), Ψ1(B) = 91.9(6)°. 121.7(6)°. The peptide bond istrans‐planar in both molecules. Side chain dispositions are essentially identical in both structures. The Met side chain adopts the zig‐zagtrans‐planar conformation while the Phe residue adopts an orientation near + 60° in agreement with rotamer populations observed by solution n.m.r. Typical peptide intermolecular H‐bondi

ISSN:0367-8377    

DOI:10.1111/j.1399-3011.1988.tb00019.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY

摘要:

The three‐dimensional structure of the immunosuppressive cyclic peptide cyclosporine (Cs), determined in crystal by X‐ray analysis and in solution in aprotic solvents by n.m.r., differs mainly by the orientation of the 7 carbon side chain of residue 1. Because of its poor solubility in water, the conformation of Cs in aqueous medium cannot be studied by n.m.r. methods, which require concentrations of the substance of the order of milligram/mL but can be analyzed by immunochemical methods in which concentrations in the nanogram/mL range are detected. In the present study, the ability of a series of monoclonal antibodies (McAbs) raised against Cs to recognize different parts of residue 1 of Cs was determined from the cross‐reactivity of different Cs‐analogues modified in residue 1. The results show that when Cs is dissolved in aqueous buffer, the terminal atoms of residue 1 side chain are not available for binding to antibodies recognizing the face of the molecule defined by residues 1, 2, 3, 10, 11, suggesting that the chain is probably folded back under the molecule, as observed in the crystal structure. Binding of McAbs to Cs was also affected by conformational modifications of the peptide ring that occur in some Cs‐analogues. The results illustrate the potential of McAbs for probing the conformation of Cs‐derivatives for which no structural data ar

ISSN:0367-8377    

DOI:10.1111/j.1399-3011.1988.tb00020.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY

摘要:

Evidence is presented for the facile acid‐hydrolytic cleavage ofC‐terminalN‐alkylated amino acid residues in peptide acids. A mechanism (defined as “back‐biting”) is proposed in which the process is initiated by a nucleophilic attack of the conjugated base of the terminal acid on the (protonated) precedingcis

ISSN:0367-8377    

DOI:10.1111/j.1399-3011.1988.tb00021.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY