ISSN:0006-3525    

DOI:10.1002/bip.1968.360060602

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

年代:1968

数据来源: WILEY

摘要:

AbstractThe dynamic viscoelastic properties of hyaluronic acid solutions have been measured over the frequency range 0.02–1.67 cps. The effects of varying temperature, hyaluronic acid concentration, pH, and ionic strength on the dynamic shear moduli were studied. The solutions exhibited a sharp transition from viscous to elastic behavior as the strain frequency increased. No entanglement coupling of the hyaluronic acid molecules was evident over the concentration range 2.0–4.0 mg./ml. Solutions at pH 2.5 showed a pronounced elastic behavior relative to both higher and lower pH's. This effect was attributed to a stiffening of the hyaluronic acid molecule at this

ISSN:0006-3525    

DOI:10.1002/bip.1968.360060603

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

年代:1968

数据来源: WILEY

摘要:

AbstractThe denaturation of single‐stranded and double‐stranded RNA's in solutions with varying proportions of dimethyl sulfoxide has been followed by changes in absorbancy, optical rotation, and—with a double‐stranded form of bacteriophage of MS2 RNA— infectivity for bacterial spheroplasts. By these criteria the RNA's studied, including the synthetic polynucleotide rG:rC, are completely denatured at room temperature in high concentrations of this solvent. In lower concentrations, theTmof the RNA preparation is decreased only slightly as the dimethyl sulfoxide concentration is raised until a critical concentration is reached. TheTmfalls sharply with small further increases in dimethyl sulfoxide concentration. Sedimentation studies can be conducted directly in these media. The determination of sedimentation velocity in 99% dimethyl sulfoxide containing 0.001MEDTA provides a reliable estimate of RNA molecula

ISSN:0006-3525    

DOI:10.1002/bip.1968.360060604

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

年代:1968

数据来源: WILEY

摘要:

AbstractElectronic excitation spectra were measured on a donor‐acceptor pair which was separated by oligomers ofL‐proline of gradually increasing lengths. The logarithmic plot of the transfer efficiency versus the donor‐acceptor separation, for (pro)noligomers withn⩾5, yielded a slope of 5.8 ± 0.3 in good agreement with the theoretical value of 6, predicted by Forster. The above method is suggested as a tool for the estimation of distances between certain chromophoric groups, covalently bound to macromolecules. The use of any stereoregular polymer for calibrating a certain energy donor‐acceptor pair is

ISSN:0006-3525    

DOI:10.1002/bip.1968.360060605

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

年代:1968

数据来源: WILEY

摘要:

AbstractTo make a comparison of some of the various polymerization methods, poly‐γ‐D‐andL‐glutamylglycine were synthesized through the mixed anhydride, carbodiimide, and pentachlorophenyl active ester methods. This last method proved to be best, on the basis of weight‐average molecular weights (M̄w). A detailed study was also carried out to determine the optimum conditions for this method. TheM̄w, values of the polymers were determined by the sedimentation equilibrium method; it was found that the pentachlorophenyl active ester gaveM̄wvalues of up to 11, 500 but the mixed anhydride and carbodiimide methods gaveM̄w, values of only about 1000. Tests with rabbit antianthrax immune serum showed that neitherD‐ norL‐isomer precipitated with the antiserum, but that, both were able to inhibit the precipitation of the antiserum by anthrax polypeptide. In addition, theD‐polymer gave more inhibition than theL, which would indicate a specificity of the antibody forD‐

ISSN:0006-3525    

DOI:10.1002/bip.1968.360060606

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

年代:1968

数据来源: WILEY

摘要:

AbstractAn alcoholysis method is described for the modification of high molecular weight poly(β‐benzylL‐asparatate); by this method the benzyl groups in the polypeptide have been replaced by methyl, ethyl, isopropyl,n‐propyl, and phenethyl groups to give a series of copolymers of each of the corresponding aspartate esters with benzylL‐aspartate. By repeating the reactions, replacement of better than 99% has been achieved in some cases to give in effect the homopolymer. Optical rotatory dispersion studies show that of all the systems studied only poly(β‐methylL‐aspartate) has the left‐handed helix sense, the others are right‐handed. It is shown further that the helix sense is not an intrinsic property of the nature of the aspartate side chain. Raising the temperature of chloroform solutions of the right‐handed form of the copolymers of benzylL‐aspartate and ethylL‐aspartate results in a transition to the left‐handed helix, the temperature of the transition being dependent on the composition of the copolymer. Also poly(β‐n‐propylL‐aspartate) undergoes a transition from the right‐ to the left‐handed helix form at 59°C. These results suggest a general pattern of behavior of poly(aspartate esters) and that with suitable conditions of solvent and temperature they may be in either t

ISSN:0006-3525    

DOI:10.1002/bip.1968.360060607

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

年代:1968

数据来源: WILEY

摘要:

AbstractThe helix‐coil transition has been studied by high‐resolution NMR for three water‐soluble polypeptides. Such systems are better models for protein behavior than those in TFA‐CDCl3solvent. An upfield shift of ∼7 cps is observed for the α‐CHpeak of poly(L‐glutamic acid) and poly‐L‐lysine as the helix content increases over the transition. No such shift is found for copoly(L‐glutamic acid42,L‐lysine28,L‐alanine30). The width of the α‐CHpeak for poly L‐lysine increases rapidly as helix content rises but for polyL‐glutamic acid and the copolymer, the width of this peak remains unchanged up to 60% helicity. This demonstrates a rapid rate of interconversion between helical and random conformations in partly helical polymer for the latter two polypeptides. All three polymers however, show no apparent α‐CHpeak at 100% helicity. Side‐chain resonance lines also broaden as helix content increases and, to a greater extent, the cl

ISSN:0006-3525    

DOI:10.1002/bip.1968.360060608

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

年代:1968

数据来源: WILEY

摘要:

AbstractRandom number methods are used to calculate helix—coil transition curves for the model of a heterogeneous polypeptide of random sequence. These curves are compared with several other calculations. The random number computations confirm the exact calculation of Lehman; among the several approximate calculations examined only that of Fixman and Zeroka agrees closely with results of the random number method over the whole range of conditions considered. Calculations are also reported of the average length of helix and coil sections in a heterogeneous molecule of random sequence which is undergoing the helix‐coil transit

ISSN:0006-3525    

DOI:10.1002/bip.1968.360060609

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

年代:1968

数据来源: WILEY

摘要:

AbstractA general method to calculate experimentally accessible thermodynamic and kinetic quantities for any type of cooperative transitions is developed. Special attention has been directed to transition curves and mean relaxation times. The procedure is applied to the most general case of nearest‐neighbor cooperativity by using the linear Ising model and the matrix method of evaluation. The various potential types of end effects arid the resulting chain length dependences are discussed in detail. The significance of the theory with respect to the helix‐coil transition of polypeptides as well as to the polyproline I‐II transition is indi

ISSN:0006-3525    

DOI:10.1002/bip.1968.360060610

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

年代:1968

数据来源: WILEY

ISSN:0006-3525    

DOI:10.1002/bip.1968.360060611

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

年代:1968

数据来源: WILEY