ISSN:0367-8377    

DOI:10.1111/j.1399-3011.1988.tb00031.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY

摘要:

Ribosomal protein L25 from the large subunit ofE. coliribosomes has been purified using a new procedure involving a 2mLiCl extraction followed by phosphocellulose chromatography in 6murea elution buffer. The conformation of purified L25 was studied employing circular dichroism and ultraviolet absorption spectroscopy in reconstitution buffer. The analysis of the far u.v. circular dichroism spectrum of L25 indicates L25 contains ∼ 16%α‐helix and ∼ 19%β‐structure. The conformation of L25 was also studied using the predictive methods of Chou&Fasman and Maxfield&Scheraga. Both of these methods predict approximately three times the percent α‐helix present in L25 as compared with that determined from the analysis of the circular dichroism spectrum. A structure for L25 is predicted which contains two positively charged binding domains and is consistent with published binding data on the interaction of 5S RNA and L25. The large difference in the %α‐helix as determined from the analysis of the circular dichroism spectrum and the predictive techniques is suggested to result from the denaturing effects of 6murea used in the preparation of rib

ISSN:0367-8377    

DOI:10.1111/j.1399-3011.1988.tb00032.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY

摘要:

The abortifacient proteins trichosanthin, α‐momorcharin and β‐momorcharin at nM concentrations inhibit cell‐free protein synthesis. The momorcharins and the ribosome‐inactivating proteins isolated fromMomordica charantiaseeds cross‐react with the respective antisera. The ribosome‐inactivating proteins saporins, pokeweed antiviral protein (PAP) and, to a lesser extent, gelonin have abortifacient activity on

ISSN:0367-8377    

DOI:10.1111/j.1399-3011.1988.tb00033.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY

摘要:

A new synthetic pathway is proposed for the preparation of keto‐methylene and dehydro‐keto‐methylene dipeptide isosteres bearing the general formulas (RS)XxxΨ(COCH2)(RS)Yyy and (RS)XxxΨ(COCH2)ΔYyy. The method involves the condensation of an oxazolone derived from anN‐benzoyl amino acid (3a, b) via a modified Dakin‐West reaction with the appropriately α‐substituted succinoyl chloride half ester (2a, b). This last compound is obtained from a Stobbe condensation followed by reaction with oxalyl chloride. The fully protected pseudo‐dehydro dipeptides (41, b) thus obtained can then be catalytically hydrogenated to the desired pseudo‐dipeptides (5a, b). Acid hydrolysis of (4) and (5) gives the pure fully deblocked dipeptide surrogates which are thenN‐protected for coupling into the desired peptide analogs. For preparative applications, the prior isolation of intermediates is not required throughout the procedure up to the final products. In this manner, the following compounds were prepared: Boc‐(RS)PheΨ(COCH2)(E, Z)Δ Phe‐OH (9), Boc‐(RS)Pheψ(COCH2)(RS)Phe‐OH (7a), and Boc‐Glyψ(COCH2)(RS)Leu‐OH (7b). Characterization of isolated intermediat

ISSN:0367-8377    

DOI:10.1111/j.1399-3011.1988.tb00034.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY

摘要:

Myoglobins from three small placental mammals and one small marsupial were isolated from cardiac or skeletal muscle. The conformational free energies of these four myoglobins were estimated from guanidinium chloride unfolding data at pH 8 and 25°. The myoglobins from rat and rabbit are more stable than that of the most stable myoglobin previously studied, that of the sperm whale. In addition, these two myoglobins unfold with greater cooperativity than previously characterized myoglobins. The data obtained herein demonstrate unequivocally for the first time that the stability of homeotherm myoglobins correlates with neither the size of the organism nor its metabolic rate

ISSN:0367-8377    

DOI:10.1111/j.1399-3011.1988.tb00035.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY

摘要:

The crystal structures of the 1:1 complexes methylguanidinium benzylhydrogenmalonate, (C2N3H8)+(C10H9O4)−, MGD.BMAL, and methylguanidinium ethylhydrogenmalonate, (C2N3H8)+(C5H7O4)−, MGD.EMAL, and of the 2:1 complex methylguanidinium sulfate, (C2N3H8)2SO4, have been determined from three‐dimensional X‐ray data. For MGD.BMAL, the complex crystallizes in the triclinic space group Pwith two formula units in a cell of dimensions a = 6.277(5), b = 8.470(3), c = 13.191(6)Å, α= 91.01(1), β= 99.64(9), γ= 90.83(5)°. The structure has been refined to a final value of R = 0.061 based on 1511 intensities. The MGD.EMAL complex is also triclinic, space group Pwith two molecules in a cell of dimensions a = 9.254(7), b = 9.625(6), c = 6.778(2) Å, α= 109.6(1), β= 100.8(1), γ= 62.7(1)Å. The crystals of this compound are of low quality, and the final value is R = 0.109 based on 706 intensities. (MGD)2SO4is orthorhombic, space group P212121, with four molecules in a cell of dimensions a = 7.100(4), b = 12.151(3), c = 13.108(2) Å. Refinement has converged to R = 0.054 based on 907 data. All three crystals exhibit extensive interionic hydrogen bonding. The hydrogen bonding in MGD.BMAL includes a Type B interaction and a Type 1 interaction, the latter being a pairwise interaction from both amino nitrogen atoms on the cation to two carboxylate oxygen atoms from the two different carboxylate groups in an anion. In MGD.EMAL, the anion participates in both a Type A and a Type B pairwise interaction with two neighboring cations. The possible implications of the hydrogen bonding patterns in these two compounds for the role of arginyl side chains in protection of γ‐carboxyglutamate residues from decarbox

ISSN:0367-8377    

DOI:10.1111/j.1399-3011.1988.tb00036.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY

摘要:

The absolute configuration of the cyclopropane phenylalanine moiety inN‐benzyloxycarbonyl‐(+)‐E‐cyclopropane‐phenylalanyl‐l‐leucine methyl ester (Z‐(+)‐▿EPhe‐Leu‐OMe) has been determined by X‐ray crystallographic methods. The conformation of the cyclopropane amino acid and its effect on the peptide is also discussed. The peptide crystallizes in the monoclinic space group P2, and the structure was solved using MULTAN and refined by block diagonal least‐squares to a present R value of 11 %. The absolute configuration of the (+)‐▿EP

ISSN:0367-8377    

DOI:10.1111/j.1399-3011.1988.tb00037.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY

摘要:

An investigation on the resistance against acids of over 30 peptides containing a repetition ofN‐alkylated amino acids has revealed the extremely facile cleavage of the peptide bond (endopeptolysis; ranking from a few minutes to 1 hour in Tfa) between the second and third residue in a sequence of threel‐imino acid residues (called “triad”)‐ This is pronouncedly so if Pro is the head member of the triad. Triads become resistant against hydrolysis, however, when both the first and second positions are occupied by Pro, and even more so if the second member isd‐MePhe. On the other hand, as an exception, diads of iminoacids preceded by Gly also are sensitive to hydrolysis. Two possible mechanisms are proposed, among which the one that is characterized by an intramolecular attack of theN‐nucleophilic site of the first residue on the peptide bond between the second and third unit and thus forming a diketopiperazine‐onium intermediate, is our preference. This sensitivity towards acidolysis and acid‐catalyzed hydrolysis should not be overlooked, not only during the planning of peptide syntheses (having especially implications during acidic deprotection protocols), but it will compromise any strategy that makes use of strong acid conditions, e.g. in chiral determinations ofN‐alkylated amino acids in peptide hydrolysates, because acidic peptide breakdown is accompanied by appreciable stereo‐mutation. Finally, the weakened resistance of iminoacid peptide chains is obviously related totrans‐cisisomerization about the first peptide bond within the triads and suggests that endopeptidases may well act initially through at

ISSN:0367-8377    

DOI:10.1111/j.1399-3011.1988.tb00038.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY

摘要:

The synthesis of fourN‐acetylN′‐methylamide cystine‐containing hexapeptides, CVPGVC, CGVVGC, CKPGEC, and CEPGKC, is described. These were used in disulfide‐exchange reactions with the peptide CVPGGC as the formal oxidant. The relative propensities for peptide cyclization were thus deduced, and the tendency toward the formation of chain‐reversal conformations was established quantitatively. An additional peptide, CVVVVC, was prepared but was never obtained as the cyclic monomer, demonstrating that the formation of chain‐reversals in this peptide was of very low probability. Incorporation of pairs of valyl residues decreased the ease of cyclization, but it appeared that conformational flexibility in the cystine‐containing hexapeptides may have compensated for substitutions which would have been expected to hinder the adoption of certain β‐turn conformations. The peptides containing ionic residues were cyclized more readily than expected, and this process was relatively insensitive to salt concentration. This observation is discussed with regard to the stabilization of β‐turns by i‐to‐(i + 3) ionic interactions in peptides and proteins. A method for blocking thiols was introduced as an improvement in the analysis of

ISSN:0367-8377    

DOI:10.1111/j.1399-3011.1988.tb00039.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY

摘要:

The thiocarboxyl group reacts with diaryl disulfides to give an unsymmetrical acyl disulfide in dimethylformamide (DMF) and a symmetrical diacyl disulfide in aqueous DMF. Both acyl disulfides react with the α‐amino group to form the peptide bond. The method was used in a new segment synthesis of α‐inhibin‐92 (α‐IB‐92) with use of 2,2′‐dipyridyl disulfide as activator. Thiocarboxyl peptides were synthesized by the solid‐phase method on 4‐[α‐(Boc‐Gly‐S)benzyl]phenoxyacetamidomethyl‐resin. The segments α‐IB‐92‐(1–34)SH (I), Msc‐α‐IB‐92‐(35–65)SH (II), Msc‐α‐IB‐92(66–92)OH (III), and Msc‐α‐IB‐92‐(35–92)OH (VI) were prepared in yields of 33, 36, 41, and 25%, respectively, with use of crystalline symmetrical anhydrides in double and triple coupling protocols. Segments I, II, and III were used in a 3‐segment synthesis of α‐IB‐92 with an overall yield based on starting resin of about 8% while a 2‐segment syn

ISSN:0367-8377    

DOI:10.1111/j.1399-3011.1988.tb00040.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY