摘要:

AbstractDiadenosine 5′,5‴‐P1,P4‐tetraphosphate (Ap4A), an intracellular regulatory nucleotide, has been found to react with the antitumor drugcis‐diamminedichloroplatinum(II) and its aqua derivative to form a single complex. This complex has been purified by high‐performance liquid chromatography and characterized by1H‐nmr and CD spectroscopy. In this complex, Ap4A takes a very particular conformation. It is an N7‐N7 chelate of the metal with the two adenines in a head‐to‐head arrangement and ananti–anticonformation of the adenosines. Platinum chelation leads to a large decrease of the Ap4A confo

ISSN:0006-3525    

DOI:10.1002/bip.360230902

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

年代:1984

数据来源: WILEY

摘要:

AbstractThe “ordinary–extraordinary phase transition” of poly(lysine), first reported by Lin et al. [(1978)Biopolymers17, 1041–1064], has been reexamined as a function of the data collection interval (Δt) and scattering angle (θ). These data suggest that the relaxation domains “split” as the ionic strength is lowered through the transition region. In contrast, fluorescence photobleaching recovery data of Ware and coworkers (personal communication) indicate the tracer diffusion coefficient is not sensitive to the “ordinary–extraordinary phase transition.” The apparent discrepancy between these two techniques is here proposed to be due to small ion effects on both the dynamics and the scattering power of t

ISSN:0006-3525    

DOI:10.1002/bip.360230903

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

年代:1984

数据来源: WILEY

摘要:

AbstractDirect difference ir spectra are presented as a function of hydration for lysozyme and α‐lactalbumin, and detailed sequential hydration molecular events identified. Despite the strong sequence homology between the two proteins, and their expected conformational similarity, the hydration behaviour of the polar groups is different for the two proteins. Using a Hill‐type analysis, we conclude that the acid groups ionize and hydrate rapidly and noncooperatively in both proteins, consistent with the known (lysozyme) and postulated (α‐lactalbumin) surface chemistry. The polar group hydration shows a clear cooperativity, which is quantitatively different in the two proteins. Complementary work suggests this cooperativity relates to a hydration‐induced “loosening up” of the lysozyme conformation at about 55 mol water/mol protein. α‐Lactalbumin appears to “open up” more easily for hydration than does lysozyme, consistent with its lower stability against thermal a

ISSN:0006-3525    

DOI:10.1002/bip.360230904

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

年代:1984

数据来源: WILEY

摘要:

AbstractThe electric field dependence (up to 21 kV/cm) of the steady‐state and decay signals has been examined on the four well‐fractionated samples of poly(γ‐benzyl‐L‐glutamate), [Glu(OBzl)]n, inN,N‐dimethylformamide at 535 nm and 20°C. Together with the data previously obtained from the reversing‐pulse electric birefringence [Ueda, K., Nomura, M.&Yamaoka, K. (1983)Biopolymers22, 2077–2090], the steady‐state birefringence and field‐free relaxation time were analyzed by a method that takes into account the polydispersity of the chain length. The weight‐average chain length, (lw), permanent dipole moment, (μw), electric polarizability anisotropy, (Δαw), and the length‐independent optical anisotropy factor were evaluated. The axial translation per residue was calculated for the [Glu(OBzl)]nhelix, but the uncertainly involved in the weight‐average molecular weights, determined from light scattering by different investigators, makes the determination of the exact conformation of [Glu(OBzl)]ndifficult. The contribution of Δαwto electric field orientation was found to be significant, since Δαwwas approximately proportional tolw. A linear relationship also exists between μwandlw, when the [Glu(OBzl)]

ISSN:0006-3525    

DOI:10.1002/bip.360230905

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

年代:1984

数据来源: WILEY

摘要:

AbstractNuclear magnetic relaxation rates of H217O,23Na+, and25Mg2+have been measured in aqueous hyaluronate solutions. The dependence on solution pH of the relaxation rates has been investigated, as well as the competition behavior of Na+with Ca2+and Mg2+. H217O and23Na+relaxation rates in chondroitin and hyaluronate solutions have been compared in the interval, 2 ≲ pH ≲ 12.5. The ion binding of hyaluronate can be fully accounted for by Coulomb interactions, with no need to involve chemical specificity. The hydration is only slighly pH dependent, and is comparable in magnitude to hydration of synthetic polyelectrolytes and monosaccharides. Ion‐binding and hydration properties of hyaluronate and chondroitin are quite similar, except at elevated pH. At alkaline pH, an increase in charge density with pH is seen in hyaluronate and, to a much lesser degree, in chondroitin, possibly due to the titration of hydroxy groups. H217O data indicate an alkali‐induced transition in both glycosamino

ISSN:0006-3525    

DOI:10.1002/bip.360230906

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

年代:1984

数据来源: WILEY

摘要:

AbstractA tractible matrix formulation is developed for the formation of intramolecular antiparallel β sheets in a homopolymer chain molecule. The formulation is applicable to chains with a finite degree of polymerization. It can readily be extended to treat specific‐sequence heteropolymers. Individual sheets may contain any number of strands, the number of residues per strand can range upward from two, and there is no artificial constraint linking the numbers of residues in adjacent strands. The weighting scheme utilizes two end‐effect parameters, denoted by τ and δ. The first parameter is associated with each residue that does not have a partner in a proceding strand, and the latter is associated with each β bend. A third parameter,t, is associated with every residue in the sheet. Conditions are described which lead to the formation of different types of sheets: (1) “sheets” comprised of isolated extended strands; (2) cross‐β fibers in which a sheet contains a large number of very short strands; (3) fibers in which a few very long strands run parallel to the fiber axis; (4) sheets comprised of several strands in which the average strand contains five residues. The fourth type of sheet resembles those found in globular proteins. It is formed when τ and δ are both small, with the ratio, τ/δ, being slig

ISSN:0006-3525    

DOI:10.1002/bip.360230907

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

年代:1984

数据来源: WILEY

摘要:

AbstractThe frequency dependences of the dielectric constant, ε′, and the loss factor, ε″, in collagen were measured at several water contents from 0.1 to 0.3 g/g collagen over a frequency range of 30 Hz to 100 kHz and at a temperature of 20°C. Remarkable dispersion was observed at the lower frequencies for higher water contents. According to accumulated results on the thermodynamic and structural investigations, the dispersion has some analogy to the surface conduction proposed by B. V. Hamon [(1953)Aust. J. Phys.6, 304–315]. An empirical relation bewteen ε″ and frequency,f, ε″ ∝︁fn, where 0

ISSN:0006-3525    

DOI:10.1002/bip.360230908

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

年代:1984

数据来源: WILEY

摘要:

AbstractFor a long time the action pattern of depolymerizing enzymes was explored by examining the distribution of products. Some attempts to interpret the data on the action of α‐amylases on amylose quantitatively have led to conflicting results. In the present work, new mathematical models are developed based on the properties of the most‐probable distribution and on the recently established fact of its partial stability at enzyme depolymerization. Published data for several α‐amylases are reexamined in light of this theoretical analysis. The theory proposed permits us to resolve a controversy concerning the interpretation of experimental data in thi

ISSN:0006-3525    

DOI:10.1002/bip.360230909

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

年代:1984

数据来源: WILEY

摘要:

AbstractWe have derived radii of gyratin,Rg, from the absolute intensity of the scattered light of mondisperse linear Col E1LiDNA in solution at various LiCl concentrations up to 5M. The second virial coefficients,A2, decrease strongly with increasing LiCl concentration, and vanish between 3 and 5MLiCl. It was thus possible to calculate a limiting value at a high salt concentration of 28.5 nm for the persistence length,a0, of LiDNA, without the necessity of applying excluded‐volume corrections. The value obtained is in good agreement with the value previously obtained for NaDNA at high NaCl concentrations, and can be identified with the high salt limit of DNA flexibility, with long‐range electrostatic interactions effectively screened. Sedimentation coefficients in the ultracentrifuge and apparent and translational diffusion coefficients (at finite and vanishing scattering vectors, respectively) from dynamic laser‐light scattering have also been obtained up to 5MLiCl. From the sedimentation and apparent diffusion,D(90), (at 90° scattering angle only) above 5M, and up to 9MLiCl, it could be shown that the solutions are stable for reasonable periods of time, and the molecular parameters vary smoothly and moderately at high salt. Conformational transitions were not observed and precipitation occurs between 9 and 1

ISSN:0006-3525    

DOI:10.1002/bip.360230910

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

年代:1984

数据来源: WILEY

摘要:

AbstractManning's counterion condensation theory has been applied to the temperature‐induced conformational transition of κ‐ and ι‐carrageenan in the solution and gel states. The formalism of the theory has been extended to transitions between conformations with charge densities below or across the counterion condensation threshold. Measurements of the dependence of the melting temperature on ionic strength, and of the enthalpy of melting, are interpreted with the theory as indicating that the conformational transition is intramolecular and that side‐by‐side dimerization of chains gives rise to the ge

ISSN:0006-3525    

DOI:10.1002/bip.360230911

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

年代:1984

数据来源: WILEY