摘要:

AbstractNew experimental data were obtained by means of circular dichroism, melting, renaturation, and kinetic experiments, upon Cu2+binding to DNA, poly dAT, and poly dGdC. They enable us to propose a model of binding giving a satisfactory explanation to all of the data found in the literature. Two types of binding sites are proposed: (a) a “sandwich” of Cu2+between two adjacent G‐C pairs giving a charge‐transfer complex, and (b) a chelate between a phosphate group and a nitrogen atom of the bases (N7of guanine and N3of cytosine at room temperature, N3of adenine after thermal opening of A‐T pair). Type (a) stabilizes the helix and keeps the two strands linked. Type (b) destabilizes the helix and explains why the kinetic rate of renaturation is the same as that of coppe

ISSN:0006-3525    

DOI:10.1002/bip.1973.360120102

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

年代:1973

数据来源: WILEY

摘要:

AbstractA statistical‐mechanical model for superhelical DNA is presented. The partition function for a DNA superhelix is written by using a combinatorial approach in order to allow for the known relation between the number of superhelical twists and the states of the base pairs in the double helix. While the theory allows any factors which might contribute to the free energy of superhelical twisting to be included in the statistical weights of the superhelical twists, only the reduction in configurational entropy is considered in this paper. Similarities between an imperfectly matched DNA double helix and a DNA superhelix are used in the derivation of expressions for the entropy of superhelical DNA. Although the partition function is presented in a general form, permitting many equilibrium properties of DNA superhelices to be treated, the application considered in this paper is the calculation of helix–coil transition curves. Several experimentally observed features of such transitions are predicted. For example, the curves are bimodal, with an early and a late transition relative to that of a nicked molecule. The results are very sensitive to the volume within which two parts of the double helix must meet when forming a superhelical twist. The free energy of superhelix formation is calculated, and the results are compared with those obtained from the data of Bauer and Vinograd for ethidium bromide intercalation. In the present model, the free energy increases less sharply with an increase in the number of superhelical twists than observed experimentally, indicating that factors other than configurational entropy probably make important contributions to the free energy of superhelix format

ISSN:0006-3525    

DOI:10.1002/bip.1973.360120103

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

年代:1973

数据来源: WILEY

摘要:

AbstractUltraviolet absorption and static fluorescence properties of hexanucleotide (Gm‐A‐A‐Y‐A‐ψp) and a dodecanucleotide (A‐Cm‐U‐Gm‐A‐A‐Y‐A‐ψ‐m5C‐U‐Gp) excised from the anticodon region of phenylalanine tRNA from yeast have been studied with respect to temperature, pH, ionic strength, and Mg2+concentration. At low temperature these oligomers have a largely stacked structure. Only the melting data of the dodecanucleotide in absence of Mg2+fit a two‐state model. From the different melting behavior of the oligonucleotides after excision of base Y, a rodlike structure of the hexanucleotide produced by stacking interactions can be concluded. The Y fluorescence increase produced by Mg2+has been used to evaluate the binding equilibria between Mg2+and the oligonucleotides. One strong binding site per oligonucleotide and a greater number of weak binding sites have been found. The fluorescence of the free base Y is not influenced by Mg2+. The dodecanucleotide enhances the ethidium fluorescence to the same extent as tRNAPheand produces comparable shifts in the excitation and emission spectra. Therefore a double helical structure for this oligomer under the assay conditions is suggested. Only weak binding of ethidium to the hexanucleotide is observed, indicating that intercalation of the dye into its structure is not favored. The data show the decisive role of the nucleobase Y in maintaining a rigid stacked structure of the anticodon nucleotides. This structure is stabilized by high

ISSN:0006-3525    

DOI:10.1002/bip.1973.360120104

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

年代:1973

数据来源: WILEY

摘要:

AbstractThe CD spectra of DNA from various sources (T2; T4; Cd;Escherichia coli; calf thymus;Streptomyces chrysomalis) were investigated. A new band Δε210in the CD spectra of glucosylated DNA of the T even phages was found. The temperature dependence of the CD spectra of DNA was obtained over a wide range of temperatures, including those of the helix–coil transition.The band Δε275for all DNAs does not appreciably change in the range of the helix–coil transition. The monotonic increase of this band before melting, and its decrease after melting is observed with an increase in temperature.The amplitude of the CD band Δε245for all the DNAs studied and Δε210(glucosylated DNA) parallels the change ofE26

ISSN:0006-3525    

DOI:10.1002/bip.1973.360120105

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

年代:1973

数据来源: WILEY

摘要:

AbstractSedimentation constant and intrinsic viscosity were measured on purified tropocollagens extracted from earthworm‐cuticle and lathyritic ratskin. A cartesian diver viscometer was used to make viscosity measurements at small shear stress and to avoid the effects of surface forces. By comparing the experimental data with the hydrodynamic theories of wormlike‐coil of Ullman a value of 1300 Å has been assigned for the persistence length of these tropocollagens. Other factors which may affect the estimate are discu

ISSN:0006-3525    

DOI:10.1002/bip.1973.360120106

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

年代:1973

数据来源: WILEY

摘要:

AbstractUsing a potato amylose fraction of 8 × 105, molecular‐weight viscosity studies were carried out at 25°C on solutions containing 0.176–0.042% polymer, 8.67 mMKI, 1% ethanol, and different concentrations of iodine. By a novel extrapolation method, the intrinsic viscosities of the amylose/iodine complex were determined under various conditions of iodine binding (0–0.133 g I2/g amylose). Contrary to the view long held in this research area, it was found that the intrinsic viscosity of amylose solutions decreases significantly upon complex formation with iodine. Taking into account the results of our previous kinetic studies, the present findings are interpreted in terms of an amylose model characterized by loose, extended helical regions which are interrupted by short disordered regions. It is proposed that the intrinsic viscosity decrease observed is due to a shortening of the linear dimension of the polymer chain. This conformation change is apparently caused by the contraction of loose helical regions of the amylose macromolecule due to the entrapment of iodine (and perhaps other) atoms inside the helical c

ISSN:0006-3525    

DOI:10.1002/bip.1973.360120107

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

年代:1973

数据来源: WILEY

摘要:

AbstractUltrasonic absorption measurements were carried out on solutions of polybenzyl‐L‐aspartate (PBLA) in chloroform–dichloroacetic acid (DCA) and in 1,2‐dichloroethane (DCE)–DCA, in the range 3.9–155 MHZ. The helix–coil transition of PBLA produces an increase of absorption which is larger in CHCl3–DCA than in DCE–DCA solutions. The influence of the solvent on the excess ultrasonic absorption suggests that solvation processes may be involved in these changes of absorption. The plots of the absorption vs. the volume fraction of DCA do not show any absorption maximum. This indicates that the ultrasonic absorption is not sensitive to the helix–coil equilibrium of PBLA in the frequency range investigated. A maximum value of 109S−1has been obtained for the rate constant of gro

ISSN:0006-3525    

DOI:10.1002/bip.1973.360120108

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

年代:1973

数据来源: WILEY

摘要:

AbstractConformation of two‐stranded DNA in H2O–methanol, H2O–ethanol, H2O–isopropanol, and H2O–dioxane solutions at different concentrations of alkaline ions has been studied with the aid of circular dichroism. The following conclusions are drawn:The conformation of DNA in H2O and H2O–methanol belongs to a family of B forms (B, C, T forms are the representatives of the family). The magnitude of the winding angle between adjacent base pairs (θ) is determined by the concentration and type of the cations. In H2O the cation action is nonspecific and leads to an increase in θ value. In 80% methanol the ions act specifically, Cs+being to stabilize a form with a greater θ value, and Li+being with a lesser one. The total θ change is likely within the limits of 33° ⩽ θ ⩽ 45°.At high content of ethanol, isopropanol, or dioxane (∼80%), but not with methanol, and in low ionic strength the conformation of DNA belongs to a family of A forms (A form is one of the members of the family) and is specified by the concentration and type of cation involved. The two‐stranded regions of RNA in H2O are also of A type and winds with the rise of cation concentration. The range of θ variation is not narrower than 30° ⩽ θ 33°.The conformational transitions within the families (induced by ions) are of non‐cooperative pattern, wheras the transitions between the families (induced by nonpolar component) are of cooperative pattern. The effect of cations, when specific, is discussed on the basis of steric correspondence between the width of DNA narrow groove

ISSN:0006-3525    

DOI:10.1002/bip.1973.360120109

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

年代:1973

数据来源: WILEY

摘要:

AbstractThe electric permittivity of alfalfa virus particles in buffer solutions of three different concentrations at pH 7 was studied between 10 kHz and 100 MHz. The experimental results could be described with one single dispersion curve of the Cole‐Cole type characterized by a concentration independent specific dielectric increment and mean relaxation time. The results were interpreted semi‐quantitatively in terms of counterions–atmosphere polarizability, neglecting counterion repu

ISSN:0006-3525    

DOI:10.1002/bip.1973.360120110

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

年代:1973

数据来源: WILEY

ISSN:0006-3525    

DOI:10.1002/bip.1973.360120111

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

年代:1973

数据来源: WILEY