摘要:

AbstractThe binding of copper(II) ions by heparin was investigated using equilibrium dialysi techniques, and the effects of this binding on solution properties determined. In neus tral Tris buffer solutions, heparin binds a maximum of twenty‐three to twenty‐four copper ions in two classes of sites, one containing three to four binding sites, the other containing twenty to twenty‐one sites. Cooperative binding is associated with the larger class of sites. In more acidic citrate buffer solution, only one class of sites is observed, containing about four to five binding sites. Association constants are calculated for the classes and the possible chemical nature of the sites is discussed. The binding of calcium ions in neutral buffer is also examined, and these ions appear to be bound by a group of twenty to twenty‐one binding sites, with a larger association constant than that for the copper ions. Definite effects on the solution properties of heparin, such as intrinsic viscosity, sedimentation coefficients, and partial specific volume, can be observed only in the cooperative binding of copper ions in neutral buffer. The interpretation of these solution properties in terms of molecular size and shape is analyzed, and it is concluded that the metal ion interactions cause no major change in the apparently random coil conformation of heparin in buffered solution, although some minor changes can be associated with the cooperative uptake of copp

ISSN:0006-3525    

DOI:10.1002/bip.1973.360120112

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

年代:1973

数据来源: WILEY

摘要:

AbstractThe dielectric behavior of the DNA molecule is investigated in the presence of mechanical force as well as the electrical field. In the present experiment, the direction of the electrical field is perpendicular to that of the mechanical force. The dipole moment of polar molecules manifest itself as dielectric increment at low frequencies or as the conductance increment at high frequencies. These two quantities are closely related to each other by Eq. (1) in the text. Because of the difficulty due to electrode polarization at low frequencies, no useful information was obtained by investigating the dielectric increment in the present system. Therefore, the effect of shear gradient was studied by measuring the conductance increment at high frequencies with various velocity gradients. The conductance increment decreased when the shear was applied perpendicular to the electrical field. The conductance change is converted into the unit of dielectric constant; it was found that the dielectric increment of DNA solution decreases by as much as 85 percent. From these observations, it is concluded that the direction of the dipole moment in DNA is longitudinal rather than transverse. The same experiment was repeated with the random coil DNA and no anisotropy in the dielectric increment was observed.

ISSN:0006-3525    

DOI:10.1002/bip.1973.360120113

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

年代:1973

数据来源: WILEY

摘要:

AbstractA semi‐empirical conformational energy calculation has been performed on the ionizable polydipeptide poly(Glu‐Ala). The results indicate that; (1)the ionized polymer assumes the lefthanded extended helix conformation is aqueous solution; (2) the poly(Glu‐Ala) extended helix is less stable than that of polyglutamic acid; (3) the unionized polydipeptide will preferentially assume the “β‐helical” conformation (isolated 21degenerate helix) in aqueous solution. These conclusions are supported b

ISSN:0006-3525    

DOI:10.1002/bip.1973.360120114

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

年代:1973

数据来源: WILEY

摘要:

AbstractRandom copolymers of sarcosine and small amounts of γ‐p‐nitrophenyl‐L‐glutamate (poly(Sar,pNPGlu)) were synthesized and their hydrolyses were investigated in buffer solutions. The reaction courses of their spontaneous hydrolyses consisted of two parts; the initial fast reaction and the subsequent slow reaction. Since the former became shorter as the chain length of copolymer increased, it was attributed to a faster hydrolysis of ester groups near the chain ends.The hydrolysis was considerably accelerated by the introduction of a pyridyl group to a chain end of the copolymer. This was explained by the intrachain catalysis, since the contribution of interchain catalysis was found to be very small. The extent of acceleration was much smaller than in the reaction along the polyacrylamide chain reported by Morawetz et al. The lesser flexibility of polysarcosine chain may account for the difference. Also in the intrachain hydrolysis a large deviation from the first‐order kinetics was observed, which indicated the different reactivities of each ester group positioned at the different separation along the chain from the terminal pyridyl group. Kinetic calculations were carried out using rate constantki, for the hydrolysis of an ester group attached to theith residue by the terminal puridyl group. It was found that the dependence ofkioni, Which is the distance between an ester group and the terminal pyridyl group, was more specific than that of intrachain rate constants for the chain effect polymerization ofDL‐phenylalanine NCA previously

ISSN:0006-3525    

DOI:10.1002/bip.1973.360120115

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

年代:1973

数据来源: WILEY

摘要:

AbstractExposure ofEscherichia coliMRE‐600 ribosomes to acridine orange (AO) at low ionic strength (1mMTris‐acetate pH 7.4) results in quantitative binding of the dye. Under our experimental conditions about a few hundred dye molecules can be bound to any one of the 30, 50, or 70‐S particles. AO causes the 30 and the 50‐S subunits to form ribosomal aggregates of approximate sedimentation constants of 70 an

ISSN:0006-3525    

DOI:10.1002/bip.1973.360120116

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

年代:1973

数据来源: WILEY

摘要:

AbstractDespite its being weaker base poly(2‐vinylpyridine) polymerizedDL‐β‐phenylalanine NCA at a much faster rate than pyridine and α‐picoline. Poly(2‐vinylpyridine) adsorbs NCA by hydrogen bonding with the cooperation of a few pyridine groups. This results in a high local concentration of NCA. The syndiotactic configuration of pyridine group seemed to be least suitable for the cooperative hydrogen bonding. Adsorbed NCA is activated to form an “activated” NCA which in turn reacts with an NCA adsorbed on the same polymer chain. Since the polymer chain is flexible, this intramolecular reaction takes place frequently, resulting in the acceleration of polymerization. The intramolecular reaction along the polymer chain is dependent on the degree of polymerization of polymer catalyst. A suitable model was proposed for the intramolecular reaction to explain the effect of degree of

ISSN:0006-3525    

DOI:10.1002/bip.1973.360120117

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

年代:1973

数据来源: WILEY

摘要:

AbstractAn attempt to elucidate the solution conformation(s) of the synthetic cyclic hexapeptide 5L‐ala·D‐ala is described. Nuclear magnetic resonance (nmr) spectra are recorded for the purpose of measuring the vicinal coupling constant between the amide and α‐protons in each residue and to observe the deuterium exchange rate and temperature dependence of the chemical shift of each amide proton. Low‐energy cyclic conformations, whose individual residues are in conformations consistent with the observed amide to α‐proton coupling constant, are searched for in an approximate theoretical treatment. The two lowest energy, alltranspeptide bond conformations generated are distinguishable by the presence or absence of a single intramolecular hydrogen bond. The observed temperature independence of the chemical shift of one of the amide protons is consistent with the presence of a single intramolecular hydrogen bond, while the observation of similar deuterium exchange rates for each of the amide protons indicates their comparable availability to solvent. Consequently, it is concluded that 5L‐ala·D‐ala is in rapid equilibrium between conformations with and without a single internal hydrogen bond and possesses considerable conformational flexib

ISSN:0006-3525    

DOI:10.1002/bip.1973.360120118

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

年代:1973

数据来源: WILEY

摘要:

AbstractTheoretical calculations of the circular dichroism of double‐helical DNA and RNA by the method of Johnson and Tinoco were performed in order to investigate the origins of the optical activity spectral differences between these polynucleotides. Calculations were performed using transition moment directions arising from molecular orbital calculations as well as a transition moment directions in agreement with experimental directions. The results of these calculations indicate that the conservative circular dichroism spectrum of B‐form DNA and the nonconservative spectrum of RNA (and A‐form DNA) arise as a consequence of the distance between the paired bases and the helix axis. The negative nonconservative spectrum of C‐form DNA was calculated and shown also to result from the distance of the paired bases from the helix axis. Several other conspicuous geometric parameters of DNA and RNA were investigated and were found to be less significant in their effects upon the spectral differences. Theoretical calculations on a four‐stranded DNA model which has paired bases similarly related to the helix axis as RNA and A‐form DNA was found to yield a low intensity, nonconservative circular dichroi

ISSN:0006-3525    

DOI:10.1002/bip.1973.360120119

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.1973.360120101

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

年代:1973

数据来源: WILEY