摘要:

AbstractA dilatometric technique is employed to measure the volume changes occurring on denaturation of collagen solutions and tendons. Partial specific volumes of tropocollagen are calculated to be 0.686 ml./g. in water and 0.689 ml/g in 0.1Mcitrate buffer. From data on non‐aqueous solutions, it is estimated that most of the volume change arises from changes in polymer configuration rather than from changes in solvatio

ISSN:0006-3525    

DOI:10.1002/bip.1967.360050802

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

年代:1967

数据来源: WILEY

摘要:

AbstractA quantity, called the linking number, is defined, which specifies the total number of twists in a circular helix. The linking number is invariant under continuous deformations of the ring and therefore enables one to calculate the influence of superhelical structures on the secondary helix of a circular molecule. The linking number can be determined by projecting the helix into a plane and counting strand crosses in the projection as described. For example, it has been shown that for each 180° twist in a left‐handed superhelix, a right‐handed 360° twist is removed from the secondary helix, thus allowing local unwi

ISSN:0006-3525    

DOI:10.1002/bip.1967.360050803

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

年代:1967

数据来源: WILEY

摘要:

AbstractWe have generated solutions to the Lamm equation to examine the effects of concentration dependence on velocity experiments. Two forms ofcdependence are considered:s/s0= 1 –kcands/s0= (1 +kc)−1. Features of these solutions are discussed. The magnitude of the errors resulting from the usual procedure of measuring the rate of movement of schlieren maxima or of the position at which the concentration is one half the plateau value have been examined. These errors are usually negligible after sufficient centrifugation time. The errors in using the half‐plateau concentration are less than those using the movement of the peak. We have also examined a technique due to Fujita for determiningDfrom boundary spreading whens/s0= (1+kc)−1. This method is satisfactory whens/s0is actually of this form, or under certain limitations whens/s0= (1 +kc)−1. Creeth has shown that under certain conditions the concentration gradient, curve remains virtually unchanged in shape after separating from the meniscus. When this occurs it is possible to estimates/Dfrom the data. The condition for such a steady state is thatkc0be sufficiently large. Numerical confirmation of this method is presented in the fina

ISSN:0006-3525    

DOI:10.1002/bip.1967.360050804

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

年代:1967

数据来源: WILEY

摘要:

AbstractThe time required for the completion of the process of strand separation in λ bacteriophage DNA preparations exposed to strongly alkaline conditions in aqueous glycerol solutions was directly proportional to the viscosity of the solvent. This finding supports the idea that the rate‐limiting step in the denaturation of high molecular weight DNA is the uncoiling of the strands and in the course of this uncoiling the forces arising from electrostatic and entropic factors must overcome the hydrodynamic viscous drag of the solvent resisting the translation of the polynucleotide stran

ISSN:0006-3525    

DOI:10.1002/bip.1967.360050805

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

年代:1967

数据来源: WILEY

摘要:

AbstractPreliminary experiments have been carried out which measure the variation in the intensity of the light scattered by DNA solutions under the influence of an electric field. Data have been collected on the length of DNA molecules, their electric polarizability, and their dispersion behavior.

ISSN:0006-3525    

DOI:10.1002/bip.1967.360050806

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

年代:1967

数据来源: WILEY

摘要:

AbstractInformation concerning the structures of rA–rU, rA–rU2rI–rC, rA–rI2, and acid rA helices in solutions is reported. Through the use of diquaternary ammonium salts of the general structure,\documentclass{article}\pagestyle{empty}\begin{document}$ {\rm R}_1 {\rm R}_2 {\rm R}_3 \mathop {\rm N}\limits^ + ({\rm CH}_2 )n\mathop {\rm N}\limits^ + {\rm R}_1 {\rm R}_2 {\rm R}_3 \cdot 2{\rm Br}^ - $\end{document}(I), it is shown that (1) the distances between adjacent negatively charged oxygen atoms on the helix increases in the following order rA–rI2

ISSN:0006-3525    

DOI:10.1002/bip.1967.360050807

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

年代:1967

数据来源: WILEY

摘要:

AbstractThe structure of gels formed from solutions of silk fibroin has been observed by electron microscopy. The gels consist of fibrils, and possible methods of formation of these fibrils are suggested.

ISSN:0006-3525    

DOI:10.1002/bip.1967.360050808

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

年代:1967

数据来源: WILEY

摘要:

AbstractA Kerr effect study is reported in which measurements have been made on the magnitudes of both the steady maxima and the decays of the birefringence of solutions of ovalbumin, bovine γ‐globulin, and β‐lactoglobulin. For each protein, results are presented on solutions covering the concentration range of 0.3–1.7 g./100 ml. in order to obtain by extrapolation, values of the specific Kerr constant Ksp, and the birefringence relaxation time τ25,wat zero concentration. The relaxation times thus obtained for ovalbumin (18.3 nsec.) and γ‐globulin (157 nsec.) have been shown to be compatible with molecular models and dimensions presented in the literature. All experiments showed the need for careful extrapolation to zero concentration if reliable parameters are to be obtained: for example a 1% solution of ovalbumin or l.5% solution of γ‐globulin, would give values for τ which are 50% too high when compared with the true value at infinite dilution. The gradual fall in τ for γ‐globulin as the pH was lowered from 6.7 to 3.0 was also studied for three solvents. Fisher's generalized model for the arrangement of the polar residues around the outside of a globular protein has been developed to account for ellipsoidal particles and has been used to demonstrate the suitability and usefulness of this treatment in predicting the conformation and dimensions of these proteins. Rather unusual birefringence traces for β‐lactoglobulin were obtained, which may indicate the dissociation of aggregates, or of the parent molecule into its subunits, under the influence of

ISSN:0006-3525    

DOI:10.1002/bip.1967.360050809

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

年代:1967

数据来源: WILEY

摘要:

AbstractAn expression is derived for the melting point of a polymer when in equilibrium with a solution in which binding of low molecular weight compounds to the polymer takes place. Allowance is made for the possibility that the crystalline polymer itself is a complex. The argument is a purely thermodynamic one and is based on a consideration of the change in free energy as a result of a change in binding. Allowance is made also for non‐specific polymer–solvent interactions, in which the mixture of low molecular weight solvents is treated as a single solvent. Special attention is paid to “inverted” melting transitions, i.e., cases in which the melting point increases with increasing dilution of the polymer. It is shown that as a rule this is accompanied by a corresponding, inverted effect of the solvent composition on the melting point. It is further shown that‐in the absence of binding, “normal” behavior at the critical point (i.e., phase separation is induced by lowering the temperature) is always accompanied by “normal” melting behavior (i.e., a decrease in melting point when the polymer is diluted). Also, “inverted” melting always implies that phase separation at the critical point is induced by heating, but the reverse is

ISSN:0006-3525    

DOI:10.1002/bip.1967.360050810

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

年代:1967

数据来源: WILEY

ISSN:0006-3525    

DOI:10.1002/bip.1967.360050811

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

年代:1967

数据来源: WILEY