摘要:

AbstractA systematic survey has been made, using molecular mechanics, of the conformation ofcyclo(‐Nγ‐Mabu‐Gly‐Ala‐Ala‐), where Mabu is (R)‐α‐methyl‐γ‐aminobutyric acid. This molecule corresponds to the 14‐membered ring of the conformationally restricted, biologically active, Leu‐enkephalin analog, Tyr‐cyclo(Nγ‐D‐A2bu‐Gly‐Phe‐Leu‐), reported by DiMaio and Schiller [(1980)Proc. Natl. Acad. Sci. USA77, 7162–7166]. There is one extensive low‐energy conformational region, in which the two lowest energy minima are separated by a low barrier; other low‐energy conformations exist but are closely restricted. Assuming that enkephalin in its active form shares conformation features with the cyclic molecule, it is deduced that enkephalin contains a Gly3‐Phe4type II′ bend and that it could be similar to the model propose

ISSN:0006-3525    

DOI:10.1002/bip.360230802

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

年代:1984

数据来源: WILEY

摘要:

AbstractThe dielectric properties of sonicated calf‐thymus DNA sodium salt in aqueous solutions have been studied in the frequency range from 40 MHz to 2 GHz by time domain spectroscopy (TDS). A dielectric dispersion not previously reported was found, which has a characteristic frequency of about 150 MHz. All of the dielectric parameters are insensitive to the size of DNA fragments and to helix‐to‐coil transitions. The study of this dispersion as a function of DNA concentration and temperature allows us to conclude that it may be due to counterion fluctuation on short sections, probably in a direction transverse to the macromolecular

ISSN:0006-3525    

DOI:10.1002/bip.360230803

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

年代:1984

数据来源: WILEY

摘要:

AbstractThe oxidation ofL‐adrenaline (epinephrine) in the presence of [Fe(tetpy)(OH)2]+ions bound to poly(L‐glutamate) or to poly(D‐glutamate) has been studied at pH 7 (tetpy = 2,2′:6′,2″:6″,2‴‐tetrapyridyl). Electron transfer from the substrate to the central metal ion, which is rate‐determining, proceeds stereoselectively only when extensive and possibly specific interactions between adrenaline and the peptidic residues of the ordered polymer in the close environment of the active sites occur. This ensures different steric constraints for the two diastereomeric precursor complexes, which are thought to affect the separation and orientation of the redox centers differently, leading to the observed phenomena. Some data on the catalytic oxidation ofL‐dopa(3,4‐dihydroxyphenylalanine) are also presented, showing stereoselective effects similar to those observed withL‐adrenaline, despite the diverse distance of the chiral center from the reacting OH groups. A mechanistic interpretation of the results is discussed in the light of a few general considerations concerning the structural features of the catalytic systems. Possible explanations for the finding that stereoselectivity occurs at the expense of the efficiency of cata

ISSN:0006-3525    

DOI:10.1002/bip.360230804

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

年代:1984

数据来源: WILEY

摘要:

AbstractMeasurements of Rayleigh scattering of Mössbauer radiation (RSMR) have been performed on syntheticL‐Dopa melanin as a function of the scattering vector,Q, and temperature,T, and are compared with the results of X‐ray diffraction analyses. The data obtained allow us to derive a radial distribution function for the atomic positions not affected by the dynamic disorder and determined only by the distribution of equilibrium interatomic distances. The mean‐square atomic displacements,, derived from the RSMR measurements, evidence a strong anisotropy of the atomic vibrations: even at room temperature,reaches fairly high values for off‐plane displacements, as compared with those for motions within the planes of the structure. A connection is suggested between the observed dynamics and the biological screening action of

ISSN:0006-3525    

DOI:10.1002/bip.360230805

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

年代:1984

数据来源: WILEY

摘要:

AbstractConformational analysis of triple helics of a type of collagen was performed with typical collagen tripeptide sequences based on Gly‐Pro‐Ala, Gly‐Ala‐Hyp, and Gly‐Ala‐Ala. During energy minimization, the possibility of continual deformation of the pyrrolidine cycle was taken into account in order to achieve better accuracy in the resulting structure. The (Gly‐Pro‐Ala)nstructure is almost isomorphic to the (Gly‐Pro‐Hyp)nstructure obtained in the previous work [Tumanyan, V. G.&Esipova, N.G. (1982)Biopolymers21, 475–497]. For a collagen‐type structure, the optimal conformation of (Gly‐Ala‐Hyp)ntends to have a decreased unit twist (t= 15°), although the energy advantage with respect to the conformation witht= 45° is not so significant. A similar situation is observed for (Gly‐Ala‐Ala)n. In this case, the energy decrease during unwinding tot= 15° fromt= 45° is quite small. The conformations of (Gly‐Ala‐Hyp)nand (Gly‐Ala‐Ala)nwitht= 15° exhibit a similarity with a triple complex of polyproline II helices—a noncoiled coil such as (Gly‐Pro‐Hyp)nand (Gly‐Pro‐Ala)n. A similar structure may be postulated for subcomponent cq1 of the first component of a human complement containing substantial Gly‐X‐Pro and Gly‐X‐Y tripeptide derivatives in the primary structure (X, Y = any amino acid). The results suggest that the observed helical symmetry of collagen (t= 36°) is a consequence of superposition of diffraction patterns (for sufficiently long segments) from various helices (tvaries from ∼15° for Gly‐X‐Hyp and Gly‐X‐Y to ∼56° for Gly‐Pro‐Ala). For short a

ISSN:0006-3525    

DOI:10.1002/bip.360230806

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

年代:1984

数据来源: WILEY

摘要:

AbstractA simple point‐charge potential, developed earlier for the calculation of intermolecular forces in molecular‐dynamics simulations of liquid water, has been extended to include interactions between water molecules and polar groups of proteins. A complete potential for use in the simulation of protein dynamics in water is repor

ISSN:0006-3525    

DOI:10.1002/bip.360230807

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

年代:1984

数据来源: WILEY

摘要:

AbstractVibrational CD (VCD) of amide I and II vibrations of several α‐helical polypeptides have been measured in solution. For the amide II as well as the amide I [previously published: Lal, B.B.&Nafie, L.A. (1982)Biopolymers21, 2161] we find the VCD to be characteristic of the polypeptide secondary structure. Amide II bands of right‐handed α helices were all found to have negative VCD and to have their maximum rotational strength for the parallel (low‐energy) component. However, left‐handed α helices formed fromL‐amino acids gave positive amide II bands at higher frequencies than found for the right‐handed helices, indicating that the VCD was sensitive to the stereochemical difference. The amide‐I VCD spectra of some deuterated right‐handed α‐helical polypeptides have a new negative feature to low frequency that does not reflect theoretical predictions but also appears to be stereochemically sensitive. Amide‐II and amide‐A VCD of a few deuterated polypeptides imply retention of the secondary‐structure‐dependent characteristics

ISSN:0006-3525    

DOI:10.1002/bip.360230808

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

年代:1984

数据来源: WILEY

摘要:

AbstractVibrational CD (VCD) of amides A, I, and II vibrations of a variety of polypeptide films have been measured. VCD of films of α‐helical and β‐sheet structures are compared in the three regions. Reproducible spectra could only be obtained for thin films free of orientation dependence. The sign and band shape of the VCD of films are not always the same as that in solution. However, the magnitude of the observed VCD seems to correlate with the secondary structure such that α‐helical molecules typically have much larger Δε/ε values than do β‐sheet molecules. The possibility of interference by artifacts owing to light‐scattering effe

ISSN:0006-3525    

DOI:10.1002/bip.360230809

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

年代:1984

数据来源: WILEY

摘要:

AbstractThe topological aspects of the conformational transformations in proteins are investigated using a new peptide‐ribbon representation of the tertiary structure. The topological parameters evaluated on a set of 49 proteins show striking regularities that extend beyond the secondary structures actually present and are interpreted as a manifestation of the topological invariance of conformational transformations in globular protein

ISSN:0006-3525    

DOI:10.1002/bip.360230810

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

年代:1984

数据来源: WILEY

摘要:

AbstractThe observed Raman and ir spectra of Ca‐poly(L‐glutamate) in the β conformation have been analyzed by means of a normal mode calculation. The force field for the main chain was transferred without refinement from β‐poly(L‐alanine), yet it provides a good prediction of the observed bands and, in particular, explains subtle differences in the spectra of these two β‐sheet structures. Main‐ and side‐chain modes are well characterized, and the dependence of the amide III frequency on side‐chain composition is

ISSN:0006-3525    

DOI:10.1002/bip.360230811

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

年代:1984

数据来源: WILEY