ISSN:0006-3525    

DOI:10.1002/bip.360250702

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

年代:1986

数据来源: WILEY

摘要:

AbstractDynamic light scattering has been used to characterize a variety of lathyritic rat skin collagen solutions. The technique was used to monitor the onset of fibril assemblyin vitroand to investigate the thermal memory effect. Although the incorporation of thermal memory was demonstrated by reheating the sample and subsequently observing a shortened turbidimetric lag phase, no significant differences between naive solutions and ones exhibiting thermal memory could be detected using photon correlation spectroscopy. This suggests that subtle changes in the state of the collagen molecules rather than extensive changes in the degree of aggregation are responsible for the thermal memory effect. During fibrillogenesis, no large‐scale changes in the distribution of monomers or aggregates occur until near the end of the lag phas

ISSN:0006-3525    

DOI:10.1002/bip.360250703

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

年代:1986

数据来源: WILEY

摘要:

AbstractWe studied the interactions of the substitution‐inert inversion‐labile complexes Fe(bipy) 32+and Fe(phen) 32+[and the inversion‐stable complex Ru(bipy) 32+] with DNA. The association of these complexes to DNA is mainly electrostatic, and Fe(phen) 32+shows a more effective binding to DNA than the two bipyridyl complexes, possibly owing to a different binding mode. The interactions are enantioselective, leading to a Pfeiffer shift in the diastereomeric inversion equilibria and an excess of the Δ‐enantiomer of Fe(phen) 32+and Fe(bipy) 32+, which is directly monitorable through CD. The partition constants for the inversion equilibrium range from 1.3 to 2.0 for Fe(bipy) 32+and Fe(phen) 32+, depending on ionic conditions. From flow LD information about the orientation of the complexes on DNA was obtained: it is consistent with a fit of the Δ‐enantiomer in the major groove of the right‐handed DNA helix. The mechanisms of interaction are discussed against equilibrium, sp

ISSN:0006-3525    

DOI:10.1002/bip.360250704

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

年代:1986

数据来源: WILEY

摘要:

AbstractA computational method for attempting to predict protein complexes from the coordinates of the individual proteins has been developed. It is based on matching complementary patterns of knobs and holes. The computer algorithm correctly and uniquely predicts the association of thealphaandbetasubunits to form the αβ dimer corresponding to the α1β1interface in the hemoglobin tetramer. It fails to correctly dock trypsin inhibitor onto trypsin. Nevertheless, this lone success is still a significant advance over previous protein‐docking algorithms. The method is also important because it introduces several ways to measure the shape of protein surface re

ISSN:0006-3525    

DOI:10.1002/bip.360250705

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

年代:1986

数据来源: WILEY

摘要:

AbstractChiral discrimination in the energetics of formation of diastereomeric pairs between iron (III)‐complex ions bound to poly(L‐glutamate) or poly (D‐glutamate) andL‐catecholamines was measured by differential microcalorimetry at 25°C. When the association of substrates by Fe–polypeptide systems was virtually complete, diastereomeric discrimination energies of a few hundred calories per mol were observed, while diastereomeric discrimination entropies were found to be negligibly small. These results are consistent with the finding that the overall stereoselectivity in the electron transfer reaction between the optically active catecholamines and enantiomeric iron(III) materials—corresponding to Δ(ΔG≠) values around 900 cal/mol—is largely controlled by transition state effec

ISSN:0006-3525    

DOI:10.1002/bip.360250706

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

年代:1986

数据来源: WILEY

摘要:

AbstractSome of the factors that govern the interaction between membrane‐active peptides and membranes were analyzed using melittin as an example. The structural properties of melittin were studied in a variety of micellar and reverse micellar assemblies of varying sizes, shapes, and net charges. The roles of the polarity, packing, and the charge carried by the host assembly on the structural features of the incorporated melittin are delineated. Such an analysis is expected to be of relevance to other membrane‐active peptides as w

ISSN:0006-3525    

DOI:10.1002/bip.360250707

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

年代:1986

数据来源: WILEY

摘要:

AbstractThe combination of ultrafiltration and difference spectroscopy allows the quantitative determination of spectra of thionine bound to heparin. The spectra of the bound dye do not depend on the degree of coverage; this and the shape of the Scatchard plot show that “all‐or‐none” binding is valid. A calculus of variations based on a modification of the Hill plot shows that aggregates of seven thionine cations are bound. Tetrasaccharides with an average charge of two carboxylate and five sulfate groups are suggested to be the binding sites. The binding constant given for one mole thionine is 4.4 · 105M−1. The Gibbs enthalpy for binding of one mole of thionine is −31.7 k

ISSN:0006-3525    

DOI:10.1002/bip.360250708

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

年代:1986

数据来源: WILEY

摘要:

AbstractThe distribution of bound Mn2+ions about poly(rI)·poly(rC) has been studied by measuring the effect of this paramagnetic metal ion on the relaxation behavior of poly(rI)·poly(rC) protons. By combining selective spin – lattice and spin – spin relaxation rates for various protons, some of the principle regions of ion association can be identified. The relaxation data on the CH6 proton are consistent with a<10% occupancy of phosphate inner‐sphere binding sites. The broadening of the imino proton resonance requires a substantial occupancy of sites located in the major groove, possibly near IN7. This would also be consistent with the observation that IH8 resonance is the proton most susceptible to relaxation by Mn2+. The relaxation data for the IH2 proton indicate a relatively low occupancy of minor‐groove binding sites (e

ISSN:0006-3525    

DOI:10.1002/bip.360250709

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

年代:1986

数据来源: WILEY

摘要:

AbstractThe unfolding ofB. subtilis5S RNA is examined by direct calorimetric measurement in the presence of various concentrations of Na+and Mg2+. The composite differential scanning calorimetry (DSC) curve is analyzed into 3–5 individual two‐state melting transitions. In the absence of added Na+or Mg2+, the 5S RNA segments melt together atTm= 40°C. Addition of Na+stabilizes the molecular structure (Tm= 56°C) and widens the melting temperature range, so that up to five component transitions are observed. Addition of Mg2+alone produces a very stable structure (Tm= 75°C) with highly cooperative melting. Finally, addition of both Na+and Mg2+produces the highest stability (Tm= 76°C). The results are interpreted according to hypothetical secondary and tertiary base‐pairing schemes. The conformational changes demonstrated here may facilitate the movement of the protein synthesis machinery during RNA tr

ISSN:0006-3525    

DOI:10.1002/bip.360250710

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

年代:1986

数据来源: WILEY

摘要:

AbstractThe polymerization of fibrin, at pH 8.5 and ionic strength 0.45, and under conditions where the action of thrombin on fibrinogen was the rate‐determining step, was interrupted by inactivating thrombin withp‐nitrophenyl‐p′‐guanidinobenzoate (NPGB). Addition of the tetrapeptide Gly‐Pro‐Arg‐Pro (GPRP) partially dissociated the fibrin oligomers as shown by subsequent ligation with Factor XIIIa and calcium ion followed by denaturation and gel electrophoresis; polyacrylamide gel electrophoresis with reduction showed a decrease in the proportion of γ‐γ ligation compared with controls untreated by GPRP, and agarose gel electrophoresis showed a shift in the distribution of oligomer sizes. The dissociation was accomplished within 15 min and its extent was consistent with establishment of an equilibrium in which two molecules of GPRP react to sever an oligomer. When GPRP was introduced into fine unligated fibrin clots by diffusion, there was some dissociation as shown by differences in the degree of γ‐γ ligation after treatment by Factor XIIIa; but the action of GPRP was much slower and less complete than on soluble oligomers. However, even a small amount of dissociation affected the mechanical properties of fine clots profoundly. The shear modulus (measured 25 s after application of stress) decreased progressively with increasing concentration of GPRP introduced by diffusion. The rate of shear creep under constant stress and the proportion of irrecoverable deformation also increased enormously. If the steadystate creep rate is interpreted in terms of an effective viscosity, the latter is decreased by up to three orders of magnitude by the presence of GPRP. In terms of transient network theories of viscoelasticity, the average lifetime of a network strand is greatly diminished. However, the total density of strands remains constant during creep and creep recovery as shown by constancy of the differential modulus or compliance. Removal of GPRP by diffusion only partially restores the original shear modulus and creep behavior of the original clot. Some limited data on the effect of the tetrapeptide Gly‐His

ISSN:0006-3525    

DOI:10.1002/bip.360250711

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

年代:1986

数据来源: WILEY