摘要:

AbstractPolyelectrolyte expansion effects on high molecular weight bacteriophage DNA have been studied by examining the influence of simple salt concentration upon the intrinsic viscosity, [η]. The viscosity–molecular weight exponent a in the expression [η]=KMadiminishes from 0.8 in 0.005Msimple salt to a limiting value of 0.6 for salt concentrations greater than 0.6Mat 25°C. The ε parameter of theN1+εhydrodynamic representation thus varies from approximately 0.2–0.07 over this range of salt concentration. The intrinsic, viscosity of DNA decreases slightly with increasing temperature at low and moderate salt concentrations but becomes independent of temperature at high salt concentrations. The expansion of the DNA molecular domain is linear in the reciprocal square root of the simple salt concentration. Viscosity differences among DNA's isolated from several bacteriophage T5 mutants reflect small differences in molecular weight which are in agreement, with sine determination by other techniques. The DNA's isolated from various rII mutants of T4 bacteriophage including some very large deletion mutations were found to be identically the same size in accord with current genetic ideas. Details of the representation and extrapolation of viscosity data are discussed and the sensitivity of the technique is e

ISSN:0006-3525    

DOI:10.1002/bip.1968.360060802

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

年代:1968

数据来源: WILEY

摘要:

AbstractThe objective have been to establish if those ions which are known to change the stability of the structure of proteins, have any influence on the properties of ionizable polypeptides. Potentiometric titrations and complementary optical rotation data are presented for aqueous solutions of poly‐L‐lysine (PLL) in the presence of KSCN, KCl, and KF, and for poly(L‐glutamic acid) (PLGA) in the presence of KSCN, KCl, and LiCl. The following measured quantities which are affected by salt concentration were obtained: intrinsic pK(pK0), slope of pKappversus degree of ionization (α) curves, the degree of ionization at which the helix to coil transition occurs, and the free energy of this transition for the uncharged molecule (δG°hel). The effects of nonspecific salts (KCl and LiCl for PLL and KSCN and KCl for PLGA) are small, and about, as expected from general electrostatic considerations. In line with the observations made with isoelectric and cat ionic collagen, specific, effects were noted with KSCN–PLL and with LiCl–PLGA. In the presence of KSCN, the poly‐L‐lysine helix becomes stabilized at much lower degree of ionization than in the presence of KCl, and the slope of the pKappversus α plots is greatly reduced. However, ΔG°hel(for the uncharged molecule) is not affected, and pK0is only slightly higher. We interpret these data in terms of binding of SCN−primarily to the side‐chain amino groups (both to RNH3+and to RNH2) solutions. (L‐glutamic acid) in LiCl solution has its transition at the same α value as in KCl solution. However, both the slopes of the pKappversus α plots and the absolute values of ΔG°helare lower than in KCl solution. We interpret these results in terms of binding of Li+to side chai

ISSN:0006-3525    

DOI:10.1002/bip.1968.360060803

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

年代:1968

数据来源: WILEY

摘要:

AbstractInfrared spectra in the region 4000–60 cm−1have been measured for acetylglycineN‐methylamide and its deuterium homologs, CD3CONHCH2CONHCH3, CH3‐CONHCD2CONHCH3, CH2CONHCH2CONHCD3, and CH3CONDCH2CONDCH3. Normal frequencies have also been calculated for these molecules with various conformations. The spectra show that this compound has two crystalline modifications, form A and form B. The frequencies and their isotope shifts show that the molecular conformation (Ψ, ϕ) of form B is near (0, 120) and that of form A near (180, 120). The short‐range factors determining the conformation of peptide backbone having glycine residues ar

ISSN:0006-3525    

DOI:10.1002/bip.1968.360060804

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

年代:1968

数据来源: WILEY

摘要:

AbstractDensity increments (∂ρ/∂c2)°μin solutions of NaDNA in NaCl and CsDNA in CsCl were determined over a wide range of salt concentrations; calf thymus DNA, fragmented by sonic irradiation to a molecular weight of 4–6 × 105was used. The partial specific volume v̄2° of NaDNA at 25°C was found to ho 0.500 ml/g in water, and that of CsDNA 0.440 ml/g. Both values increase with increasing NaCl and CsCl concentration. Refractive index increments under various experimental conditions were also determined. The relevance of the density increments (at constant, chemical potential of diffusible solutes) to equilibrium sedimentation in a density gradient and the evaluation of molecular weights is discussed. Distribution coefficients of diffusible components, sometimes referred to as preferential solvation or net hydration, were derived from the density increments and partial volumes and compared with direct experimental results, whenever available, from membrane distribution and isopiestic distillation. The thermo‐dynamic significance of the distribution coefficients as well as possible interpretations in terms of specific molecular mechanisms

ISSN:0006-3525    

DOI:10.1002/bip.1968.360060805

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

年代:1968

数据来源: WILEY

摘要:

AbstractA model for hemoglobin is proposed and its application to allosteric enzymes is discussed with particular reference to asparate transcarbamylase. The main assumptions made are that the molecule is composed of subunits and that occupation of a sub‐unit produces a conformational change which affects the occupational probability of neighboring subunits. The results compare favorably with experiment and a number of specific predictions are made for aspartate transcarbamylas

ISSN:0006-3525    

DOI:10.1002/bip.1968.360060806

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

年代:1968

数据来源: WILEY

摘要:

AbstractComplexes of amylose withn‐butanol were prepared both as crystalline precipitates and as oriented fibers. These complexes were subjected to x‐ray analysis, their unit cells were calculated, and the space group ofP212121was confirmed.n‐Butanol complexes exist in both hydrated and anhydrous forms. There is no evidence for methanol, ethanol, orn‐propanol structures similar to those shown by then‐butanol complex. The Complexes are unstable in the open air and revert to V‐amylose hydrate

ISSN:0006-3525    

DOI:10.1002/bip.1968.360060807

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

年代:1968

数据来源: WILEY

摘要:

AbstractThe correlation between mechanical and chemical Processes in the contractile system collagen fibers–aqueous KCNS sulutions was investigated. Melting and contraction of the fibers were induced by applying a force sufficiently high as to prevent melting in a KCNS solution and then decreasing it either suddenly, or continuously at a constant rate. The kinetics of both processes are characterized by an initial rapid elastic response of the crystalline collagen, followed by a stationary region. The force–velocity relationship in this region was found to be the same under different types of mechanical deformations. It is probable that under the prevailing conditions, the behavior in the stationary state is determined by the melting process and is not markedly influenced by diffusional changes. Part of the experimental data could be explained by assuming a linear, rigid model or, better, by taking into account the highly elastic properties of the amorphous collagen. The kinetic, unit seems to be composed of several hundred amino acid resid

ISSN:0006-3525    

DOI:10.1002/bip.1968.360060808

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

年代:1968

数据来源: WILEY

摘要:

AbstractCollagen fibers were contracted “chemically,” i.e., by transferring them from water into KCNS solutions either isometrically or isotonically. Both changes in force and fiber length and in salt and water contents were measured as functions of time. The mechanical changes were found to follow the diffusional processes. The diffusion of water exhibited a plasmolytie effect. The role of water in the melting process is discus

ISSN:0006-3525    

DOI:10.1002/bip.1968.360060809

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

年代:1968

数据来源: WILEY

摘要:

AbstractThe dynamic elastic behavior of collagen fibers treated by LiBr solutions was studied by the method of free longitudinal vibrations. The frequency response functions and the stress–strain relationship were evaluated for fibers denatured to different extents by various concentrations of the salt solution. The James and Guth model for rubber elasticity was applied to the experimental data. The elastometric parameter β, which is a measure of the degree of folding of the macromolecular chains, was found to decrease on increasing the salt concentration. It might thus serve as a characteristic of the degree of denaturation of fibrillar protei

ISSN:0006-3525    

DOI:10.1002/bip.1968.360060810

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

年代:1968

数据来源: WILEY

摘要:

AbstractStudies have been made of the contraction of collagen fibers in acetone due to the action of LiBr. No contraction occurs unless a small amount of water is added; on further increase of the water concentration, the fibers relax. The first contraction is irreversible. The effect of water is discussed in terms of hydrate formation.

ISSN:0006-3525    

DOI:10.1002/bip.1968.360060811

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

年代:1968

数据来源: WILEY