摘要:

AbstractThe changes in conformation undergone by α‐gelatin molecules on quenching aqueous solutions to below the temperature at which they can gel have been monitored by nuclear magnetic resonance and dielectric relaxation techniques. The relative rates of these conformational transitions are compared with changes in rheological properties. The nmr spectral intensity changes for 0.2 and 0.5% w/v α‐gelatin solutions correspond to a unimolecular process withk∼ 10−2min−1at 15°C; this process occurs independently of whether or not the solution is concentrated enough to form a gel. The process involves a slow intramolecular nucleation step, followed by a rapid conformational change of the whole molecule from random coil to a rigid stage. Comparison with other data suggests that the transition gives rise to a triple collagen‐like helix. In dilute solution (but above the critical concentration for gel formation, e.g., 0.5% w/v), the gelatin processfollowsthe formation of the rigid molecular species. It probably involves the formation of junction zones consisting of three polypeptide chains in a collagen‐like triple‐helical conformation. These junctions may form, at low concentrations, from a reorganization of previously formed, intramolecular, triple helices. Solutions below a concentration of about 0.4% w/v α‐gelatin cannot gel by this mechanism, and only

ISSN:0006-3525    

DOI:10.1002/bip.1975.360141002

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1975

数据来源: WILEY

摘要:

AbstractKinetics of proton transfer between lysozyme and a pH indicatorp‐nitrophenol (p‐Np) were measured by the temperature‐jump method in a pH range of 6.0–7.0. Two well‐defined relaxation processes were observed. The fast process (τ ≃ 15 μsec) was also observed for a lysozyme derivative succinylated at the terminal α‐amino group of Lys 1. Therefore, the fast process was found to be attributable to the proton transfer reaction of His 15 withp‐Np. The slow process (τ ≃ 50 μsec) was found to be characteristic of the proton transfer reaction of Glu 35, because it disappeared completely in solution containing a lysozyme derivative having an ester crosslink between the carboxyl group of Glu 35 and indol C‐2 of Trp 108. The rate constants for proton transfer from Glu 35 and His 15 top‐Np were found to be 9 × 106/sec/M (±65%, 23°C) and 3 × 108/sec/M (±20%, 25°C), respectively. These data indicate that the proton of the carboxyl group of Glu 35 is ki

ISSN:0006-3525    

DOI:10.1002/bip.1975.360141003

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1975

数据来源: WILEY

摘要:

AbstractThe circular dichroism of Ac‐(Ala)x‐OMe and H‐Lys‐(Lys)x‐OH withx= 1, 2, 3, and 4 has been measured in aqueous solutions. The oligomers withx= 4 show similar circular dichroism spectra in water when the lysyl amino groups are protonated, and they respond in similar fashion to heating and to sodium perchlorate. Both oligomers at 15°C exhibit a positive circular dichroism band at 217–218 nm, which is eliminated by the isothermal addition of 4Msodium perchlorate or by heating. The positive circular dichroism of the lysine oligomer is also eliminated when the pH is elevated to deprotonate the amino groups. Positive circular dichroism is still observed for Ac‐(Ala)4‐OMe at elevated pH. Circular dichroism spectra have been estimated for poly(L‐alanine) and poly(L‐lysine) as statistical coils under the above conditions, based on the trends established with the oligomers. Poly(L‐lysine) and poly(L‐alanine) are predicted to exhibit similar circular dichroism behavior in aqueous solution so long as the lysyl amino groups are protonated. The circular dichroism of the statistical coil of poly(L‐lysine), but not poly(L‐alanine), is predicted to change when the pH is elevated sufficiently to deprotonate the lysyl amino groups. These results suggest that theunionizedlysyl side chains participate in interactions that are not available to poly(L‐alanine). Hydrophobic interactions may occur between the unionized lysyl side chains. Protonation of the lysyl amino groups is proposed to disrupt these interactions, causing poly(L‐alanine) and protonated poly(L‐lysine) to have sim

ISSN:0006-3525    

DOI:10.1002/bip.1975.360141004

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1975

数据来源: WILEY

摘要:

AbstractThe preparation and characterization of α‐L‐glutamic acid oligomers with degree of polymerization (DP) up to 12 are described. The preparation of polymers with low DP corresponding to variousA/Iratios (whereAandIare monomer and initiator concentrations, respectively) with end groups blocked is given. The conditions of the fractionation, which separates the different oligomers by ion‐exchange chromatography, are discussed. Finally, the isolation from salt solutions of the pure acidic form is given. Each polymer obtained for a givenA/Iis characterized at the end of the polymerization by its molecular‐weight distribution. The average DP values calculated are compared to theA/Ivalues; agreement is very good. Potentiometric behaviour during neutralization is obtained as a function of the degree of polymerization and the elaboration of the polyelectrolytic phenomenon is d

ISSN:0006-3525    

DOI:10.1002/bip.1975.360141005

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1975

数据来源: WILEY

摘要:

AbstractThe classical potential energy of 2′‐O‐methyl cytidine was calculated using contributions from van der Waals', electrostatic, and torsional terms. All five conformational angles, namely χ, Ψ, the methoxy anglesm1andm2which are unique toO′‐methylated nucleosides, and the sugar puckerPwere varied simultaneously, and the energy was minimized with respect to these parameters. An extensive search of conformation space was made, particularly with respect to the sugar pucker. At the predicted global minimum, χ and Ψ areanti‐gg,Pis C(2′)‐endo‐C(3′)‐exo, and the methyl group is staggered with respect to the sugar. This calculated minimum agrees very well with the recently determined crystal structure of 2′‐O‐methyl cytidine. Thus, 2′‐O‐methylation still permits the conformational regions of the common nucleosides to be adopted. However, we infer that the predicted C(2′)‐endosugar pucker results from the added methyl group, since cytidine is C(3′)‐endoin the crystal, and the common ribopyri

ISSN:0006-3525    

DOI:10.1002/bip.1975.360141006

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1975

数据来源: WILEY

摘要:

AbstractSynthesis of nonapeptide hydrazide (sequence 93–101), [Thr107]‐decapeptide (sequence 99–108), [Thr107]‐tridecapeptide (sequence 96–108), [Thr107]‐hexadecapeptide (sequence 93–108), [Thr107]‐heptacosapeptide (sequence 82–108), andNα‐benzyloxycarbonyl‐[Thr107]‐dotetracontapeptide (sequence 67–108) of the proposed primary structure of baker's yeast iso‐1‐cytochrome c are described. Evidence is presented to indicate that these material

ISSN:0006-3525    

DOI:10.1002/bip.1975.360141007

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1975

数据来源: WILEY

摘要:

AbstractCircular dichroism studies on synthetic peptides related to the C‐terminal region of yeast iso‐1‐cytochrome c were carried out and compared with conformational studies on horse cytochrome c fragments. Evidence is presented for a weaker predisposition for ordered structure in the former peptides when compared with the corresponding region in horse cytochrome c. These findings agree with theoretical predictions and with observations that yeast and other mammalian type cytochromes c differ in several minor res

ISSN:0006-3525    

DOI:10.1002/bip.1975.360141008

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1975

数据来源: WILEY

摘要:

Abstract5′‐8NH2GMP forms an ordered structure in moderately acid (pD4.7) solution. We propose for this ordered form a novel hemiprotonated G·G structure with a twofold rotation axis and three hydrogen bonds between each pair of guanine residues. Gel formation does not occur with this nucleotide in either neutral or acid solution. In neutral solution 5′‐8NH2GMP also forms a regular, ordered structure, quite different from the acid form and similar to that formed by 5′‐GMP under the same neutral conditions. We suggest that this ordered structure consists of a regularly stacked array of planar tetramers, similar to that proposed for 3

ISSN:0006-3525    

DOI:10.1002/bip.1975.360141009

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1975

数据来源: WILEY

摘要:

AbstractA polarimetric electric‐field‐jump relaxation apparatus is described and used to determine the relaxation spectrum for the helix–coil transition of poly(α,L‐glutamic acid) in water at 24°C. A maximum relaxation time of 1.7 μc occurs at the transition midpoint (pH = 5.9) yielding a rate constant for helical growth of 6

ISSN:0006-3525    

DOI:10.1002/bip.1975.360141010

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1975

数据来源: WILEY

摘要:

AbstractPoly‐β‐benzyl‐L‐aspartate (poly[Asp(OBzl)]) forms either a lefthanded α‐helix, β‐sheet, ω‐helix, or random coil under appropriate conditions. In this paper the Raman spectra of the above poly[Asp(OBzl)]conformations are compared. The Raman active amide I line shifts from 1663 cm−1to 1679 cm−1upon thermal conversion of poly[Asp(OBzl)] from the α‐helical to β‐sheet conformation while an intense line appearing at 890 cm−1in the spectrum of the α‐helix decreases in intensity. The 890 cm−1line also displays weak intensity when the polymer is dissolved in chloroform–dichloroacetic acid solution and therefore is converted to the random coil. This line probably arises from a skeletal vibration and is expected to be conformationally sensitive. Similar behavior in the intensity of skeletal vibrations is discussed for other polypeptides undergoing conformational transitions.The Raman spectra of two cross‐β‐sheet copolypeptides, poly(Ala‐Gly) and poly(Ser‐Gly), are examined. These sequential polypeptides are model compounds for the crystalline regions ofBombyx morisilk fibroin which forms an extensive β‐sheet structure. The amide I, III, and skeletal vibrations appeared in the Raman spectra of these polypeptides at the frequencies and intensities associated with β‐sheet homopolypeptides. Since the sequential copolypeptides are intermediate in complexity between the homopolypeptides and the proteins, these results indicate that Raman structure–frequency correlations obtained from homopolypeptide studies can now be applied to protein spectra with greater confidence.The perturbation scheme developed by Krimm and Abe for explaining the frequency splitting of the amide I vibrations in β‐sheet polyglycine is applied to poly(L‐valine), poly‐(Ala‐Gly), poly(Ser‐Gly), and poly[Asp(OBzl)]. The value of the “unperturbed” frequency,V0, for poly[Asp(OBzl)] was significantly greater than the corresponding values for the other polypeptides. A structural origin for this difference may be displacement of adjacent

ISSN:0006-3525    

DOI:10.1002/bip.1975.360141011

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1975

数据来源: WILEY