摘要:

AbstractThermal denaturation and renaturation of directly mixed and reconstituted polylysine–DNA, directly mixed polylysine–nucleohistone complexes, and NaCl‐treated nucleohistones in 2.5 × 10−4MEDTA, pH 8.0 have been studied. At the same input ratio of polylysine to DNA, the percent of renaturation of free base pairs in a directly mixed polylysine–DNA complex is higher than that in a reconstituted complex. For a directly mixed complex, the renaturation of free base pairs is proportional to the fraction of DNA bound by polylysine or inversely proportional to the sizes of free DNA loops. A of large amount of renaturation of free base pairs has also been observed for 0.6Mand 1.6MNaCl‐treated nucleohistones. The binding of polylysine to nucleohistone enhances the renaturation of histone‐bound base pairs. The percent of renaturation of polylysine–bound base pairs is high and is approximately independent of the extent of binding on DNA by polylysine. This is true in polylysine–DNA complexes prepared either by reconstitution or by directly mixing. It also applies for polylysine–nucleohistone complexes.The model where polylysine‐bound base pairs collapse atTm′ with two complementary strands still bound by polylysine is favored over the model where polylysine is dissociated from DNA during melting. The low renaturation of histone‐bound base pairs in nucleo‐histone indicates that either histones do not hold two complementary strands of DNA tightly or that histones are fully or partially dissociated from DNA when the nucle

ISSN:0006-3525    

DOI:10.1002/bip.1974.360130402

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

年代:1974

数据来源: WILEY

摘要:

AbstractDNA from bacteriophage T7 was irradiated at long ultraviolet wavelengths in the presence of silver ions. Such treatment leads to selective production of thymine: thymine dimers in DNA. The DNA was melted and the renaturation rate was determined as a function of thymine dimer content and renaturation temperature. Under “normal” hybridization conditions little change in the renaturation rate was observed even when 30% of the thymine was dimerized. This result is consistent with the view that up to a 15% change in the primary sequence of DNA dose not appreciably change the renaturation r

ISSN:0006-3525    

DOI:10.1002/bip.1974.360130403

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

年代:1974

数据来源: WILEY

摘要:

AbstractThe thermoelastic properties of elastin immersed in water or in aqueous solutions of alcohols closely resemble those of typical polymers in the rubber elastic state. The evolution of heat much in excess of the work performed on elastin when it is stretched while immersed in water at ca. 25°C is attributable to the exothermic heat of dilution by water absorbed into the polymer during elongation. The negative sign of the temperature coefficient of swelling is confirmatory of this explanation. A network of random chains within the elastin fibers, like that in a typical rubber, is clearly indicated. The elastic properties of elastin are not explicable in terms of a two‐phase model consisting of discrete globules of compact elastin molecules fused one to another by cross‐linkages, with diluent (water) filling the interst

ISSN:0006-3525    

DOI:10.1002/bip.1974.360130404

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

年代:1974

数据来源: WILEY

摘要:

AbstractInterpreting the data of Kobayashi et al.1on the thermal transitions of triple helices of (gly‐pro‐pro)nforn= 10, 15, and 20 using a simple model of unzippering and chain dissociation, the thermodynamic parameters characterizing gly‐pro‐pro triple‐helix formation have been determined. The enthalpy and entropy of triple‐helix formation per repeating unit are found to be −7.4 ± 0.8 kcal/mol and −20 ± 2 eu, respectively. Using these parameters, the nature of the unwinding has been investigated for chains containing up to 300 triplets; it is found that there is only a minor amount of helix unwinding from the ends, the major change in helical content arising from chain dissociation. Experimental data on the melting temperatures of natural collagens as a function of imino‐acid composition are used together with the thermodynamic parameters for (gly‐pro‐pro)nto estimate the thermodynamic parameters for triple‐helix formation of amino versus imino acids (the parameters for the former being found to be similar to those for α‐helix formation). Calculations are given using these parameters for model specific‐sequence collagens; it is found that heterogeneity can have a significant influence on the nature of the

ISSN:0006-3525    

DOI:10.1002/bip.1974.360130405

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

年代:1974

数据来源: WILEY

摘要:

AbstractThe chiroptical properties ofL‐3‐methyl‐2,5‐diketopiperazine (L‐alanylglycyl anhydride) are examined on a theoretical model in which the electronic wave functions are obtained from semi‐empirical all‐valence‐shell molecular orbital calculations. The INDO molecular orbital model is used to perform SCF‐MO calculations on the ground states of six conformation isomers ofL‐3‐methyl‐2,5‐diketopiperazine and two chiral conformational isomers of unsubstituted 2,5‐diketopiperazine. Excited‐state wave functions are constructed in the virtual orbital‐configuration interaction approximation. The rotatory strengths, dipole strengths, oscillator strengths, and dissymmetry factors of the first eight singlet–singlet transitions for each of the eight structures are calculated and reported. Additionally, ground‐state dipole moments, net atomic charges, and the first four ionization potentials (calculated according to Koopman's theorem) are computed for each structure. The signs and the magnitudes of the rotatory strengths are found to be extremely sensitive to the conformation of the piperazine ring as well as to methyl substitution at the α carbon of the ring. Spectra–structure relationships based on the calculations reported here are discussed, and the available experimental CD data on dissymmetric 2,5‐diketopiperazine are exam

ISSN:0006-3525    

DOI:10.1002/bip.1974.360130406

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

年代:1974

数据来源: WILEY

摘要:

AbstractCertain discrepancies in measured heats of helix–coil transitions in polypeptides are examined in terms of the theory of the effect of solvent composition on transition temperatures and heats in such systems. It is found, generally, that disagreement between enthalpy measurements conducted at fixed solvent compositions and isothermally may be expected because of the possibility of incomplete conversion of the polypeptide from the random‐coil to the helical conformations, or vice versa in one, or both, of these regimes in the course of the transition. The magnitude of the disagreement, if any, can depend quite critically on the particular region in the transition temperature–solvent composition plane in which measurements are undertaken. Application of these results to the system, poly‐γ‐benzyl‐L‐glutamate–dichloroacetic acid‐1,2‐dichloroethane, however, suggests that previously observed discrepancies in enthalpies here cannot be attribute

ISSN:0006-3525    

DOI:10.1002/bip.1974.360130407

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

年代:1974

数据来源: WILEY

摘要:

AbstractIf dispersion effects are not taken into account, the dimensions of particles in suspension estimated from spectrophotometric data (slope of the log OD versus log λ plot) are too low. By measuring dispersion curves for the medium and for the suspension, a consistent estimate of the size of latex particles of different diameter is obtained from the OD data

ISSN:0006-3525    

DOI:10.1002/bip.1974.360130408

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

年代:1974

数据来源: WILEY

摘要:

AbstractThe helix–random‐coil transition process for poly‐γ‐benzyl‐L‐glutamate (PBG) in solvent mixtures trifluoroacetic acid/deuterochloroform (TFA/CDCl3) at different temperatures has been studied by nmr. The chemical shift behavior of the α‐CH resonances of the peptide chain and of the TFA carboxylic prot

ISSN:0006-3525    

DOI:10.1002/bip.1974.360130409

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

年代:1974

数据来源: WILEY

摘要:

AbstractThe mechanical properties of gelatin films were studied in relation to the effect of water, and compared with those of collagen films. The S‐shaped sorption isotherm was separated into an adsorption curveC1and dissolution curveC2. From theC2curve, the interaction parameter χ1of Flory–Huggins' equation was calculated. The χ1of gelatin were larger than those of collagen at low relative humidities (RH), while they coincided with each other at high RH. It was found that a composite curve was made by shifting stress relaxation curves obtained at different humidities along the log time axis. The shift factor for the formation of the composite curve was analyzed by Fujita–Kishimoto's equation, which was based on the free volume theory. The parameter β, which expressed the extent of the contribution of sorbed water to the increase in the free volume of the system, was 0.05 in the range ofC2from 0 to 0.08 (0–65% RH). This value was much smaller than 0.16 for collagen. The value was 0.16 in the range ofC2higher than 0.08, which was equal to that of the collagen. Dynamic shear modulusG′, loss modulusG″, and tan δ were determined as functions of RH. The gelatin film extended more than 100% at 73% RH under the very small stress of about 107dyn/cm2. This corresponds to the region where β changes from 0.05 to 0.16, although such a phenomenon was not observed in the collagen film. The wide‐angle X‐ray pattern of extended gelatin was similar to that of rena

ISSN:0006-3525    

DOI:10.1002/bip.1974.360130410

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

年代:1974

数据来源: WILEY

摘要:

AbstractThe helix–coil transition of poly‐N5‐(3‐hydroxypropyl)‐L‐glutamine in methanol–water solutions has been observed using13C nuclear magnetic resonance. Two signals appear in the α‐CH region in the course of the transition; this is in contrast with previous proton magnetic resonance experiments carried out on this polymer in the sam

ISSN:0006-3525    

DOI:10.1002/bip.1974.360130411

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

年代:1974

数据来源: WILEY