bluuebunny/crossref_metadata_2025_split huggingface dataset:
Molecular conformation of poly‐S‐carboxytmethyl‐L‐cysteine in aqueous solutions
Authors: Ikeda Shoichi 
Published: December 2004

AbstractPoly‐S‐carboxymethyl‐L‐cysteine has been prepared by debenzylation of poly‐S‐carbobenzoxymethyl‐L‐cysteine with hydrogen bromide in acetic acid. By the infrared spectroscopic method the polymer is found to be in the extended β‐conformation with an antiparallel arrangement of polypeptide chains in solid film, if it has been regenerated from dimethyl sulfoxide solution. Aqueous solutions of the polymer have been investigated by measurements of optical rotatory dispersion and viscosity. Various properties sharply change around pH 5 at different ionic strengths. By combining these with infrared studies in D2O solutions, it has been shown that the polymer exists in the random coil conformation at higher ionization but associates into the intermolecular β‐conformation at lower ionization. At the lowest pH attainable in solution, the β‐form is partly converted into the random coil as the temperature is raised. The rotatory dispersion of the polymer is described by the Moffitt equation. While the random coil form has a large negative a0 value and a zero b0 value, the β‐form is characterized by a positive a0 value and a negative b0 value, −130°.
Volume change on formation of native collagen aggregate
Authors: Cassel James M. , Christensen Richard G. 
Published: December 2004

AbstractThe volume change which occurs in dilute tropocollagen solution as a result of the phase transition producing the “native” form of collagen aggregate has been measured dilatometrically. A volume increase of 0.8 × 10−3 ml./g. collagen in phosphate buffer (pH 7–7.5) was determined. The volume expansion is attributed to a reduction in the organization of water molecules around nonpolar surfaces of the individual tropocollagen units. This volume expansion is consistent with a previous hypothesis that hydro‐phobic bonding is the driving force in this collagen aggregation.
X‐Ray diffraction of oriented amylose fibers. I. Amylose dimethyl sulfoxide complex
Authors: French A. D. , Zobel H. F. 
Published: December 2004

AbstractThe amylose–dimethyl sulfoxide complex has been investigated with the aid of x‐ray diagrams of oriented fibers. The amylose occurs in a six‐residue helix with alternate “up” and “down” chains packed in a square array, that is, pseudo‐tetragonal. A unit cell is proposed with a = b = 19.21 A. and c = 8.12 A.
Interaction of polynucleotides with aromatic hydrocarbons
Authors: Isenberg I. , Baird S. L. , Bersohn R. 
Published: December 2004

AbstractDNA in its native and denatured form and yeast RNA complex individual aromatic hydrocarbon molecules but single‐stranded poly A does not. The degree of complexing appears to depend on molecular dimensions; it is appreciable for phenanthrene, pyrene, and benzpyrene but very small or undetectible for coronene, tetracene, pentacene, and 20‐methylcholanthrene.
Influence of counterions radius on the polymerization of actin
Authors: Botré C. , Borghi S. , Marchetti M. , Baumann M. 
Published: December 2004

AbstractThe G–F transformation of actin was studied in terms of an interaction between different counterions and actin. macroion by means of electrometric measurements. Due to the polyelectrolyte‐structure of the actin molecule, the electrostatic interactions must play a predominant role. In this sense the influence of the counterion radius has been investigated.
Infrared absorption of tyrosine side chains in proteins
Authors: Bendit E. G. 
Published: December 2004

AbstractPoly‐L‐tyrosine absorbs strongly at 1515 cm.−1, and a band at this frequency has been found in a number of proteins and has been assigned to the tyrosine residue. The assignment was confirmed by examination of spectra of deuterated proteins, which usually exhibit a residual band at 1513 cm.−1. In proteins, this band correlates linearly with known tyrosine content, but the point corresponding to poly‐L‐tyrosine itself does not fall on the correlation line. The possibility and limitations of using the infrared method for tyrosine determinations is discussed.
Conformation of horse heart ferricytochrome c. III. Comparative optical rotatory dispersion study of the protein with its derivative heme undecapeptide
Authors: Saludjian P. , Shechter E. 
Published: December 2004

AbstractThe optical rotatory dispersion of horse heart ferricytochrome c and of a ferri heme undecapeptide have been determined under various conditions. Analysis of the Soret region makes it possible to characterize three different states of ferricytochrome c. the native state (superposition of a negative and a positive Cotton effect); an intermediate state (single positive Cotton effect whose magnitude Δ[M] is equal to 55,000); a denatured state (single positive Cotton effect whose magnitude Δ[M] is equal to 115,000) in which compared to both the native and intermediate states a more or less important decrease in helix content is observed. The optical rotatory dispersion spectra of the Soret region of the monomeric ferri heme undecapeptide is similar to that of denatured ferricytochrome c. The multiplicity of Cotton effects observed under certain conditions for the hemopeptide is a consequence, resulting from a polymerization, of intermolecular interactions. The comparison of the optical rotatory dispersion spectra of ferricytochrome c and the ferri heme undecapeptide indicates that in the intermediate state interactions remain between the heme group and the portion of the poly pep tide chain absent in the hemopeptide. These interactions disappear in the denatured state.
Influence of reductants upon optical characteristics of the DNA–Cu2+ complex
Authors: Minchenkova L. E. , Ivanov V. I. 
Published: December 2004

AbstractThe addition of reducing agents, i.e., ascorbic acid or sodium borohydride, to a DNA solution containing Cu2+ ions causes changes in the DNA absorption spectra which are due to a new absorption band with a maximum at 280 mμ assigned to a DNA base–Cu1+ complex. The stoichiometry of the complex is one Cu1+ ion per four bases of DNA. The DNA–Cu1+ complex has an increased melting temperature and rather different circular dichroism curve as compared with DNA itself. It is inferred that the above effects are caused by proton transfer along the hydrogen bond from guanine to cytosine under complexing of Cu1+ ions with the N7 atom of the guanine of DNA.
Hydrophobic fluorescent group coupled to Taka‐amylase A. Change of its environment accompanying splitting of disulfide bonds
Authors: Takagi Toshio , Nakanishi Yoshiko , Okabe Nobuo , Isemura Toshizo 
Published: December 2004

AbstractNative Taka‐amylase A (α‐amylase produced by Asp. oryzae) was coupled with 1‐dimethylaminonaphthalene‐5‐sulfonyl chloride. When disulfide bonds of the modified enxyme were split by reduction or by reduction and subsequent carboxymethylation, its fluorescent properties changed markedly. It was suggested that the hydrophobic dye group is incorporated into a hydrophobic region as the consequence of the flexibility gained by the polypeptide chain by the cleavage of disulfide bonds.
Conformations of copoly(γ‐benzyl L‐glutamate–O‐benzyl‐L‐serine)
Authors: Imahori Kazutomo , Inouye Hiroshi 
Published: December 2004

AbstractFour samples of copolymers of γ‐benzyl is L‐glutamic (BLG) and O‐benxyl‐L‐serine (BLS) were synthesized by changing the mixing ratio of two monomer anhydrides. The conformations of these copolymers in CHCl3, containing very small amount of dichloroacetic acid (DCA) necessary to dissolve the sample, were determined by their compositions; the copolymer which is rich in BLG is mostly helical and one which is rich in BLS is mostly in the β conformation. However, in DCA solution the conformations of these copolymers are independent of their composition. The interesting observation was that the copolymer which has least con tent of BLS is richest in β‐conformation.
Transient distributions arising from initially sharp boundaries in the ultracentrifuge
Authors: Charlwood P. A. 
Published: December 2004

AbstractAn infinite series solution to the Mason‐Weaver equation is presented for the case in which a synthetic boundary is formed originally between solution and solvent. Digital computations based on this series, and confirmed independently, have been made for a range of parameters. For given conditions, the maximum rate of change of concentration at the meniscus and the time at which it occurs can be easily estimated by means of the curves presented. In equilibrium experiments which commence with formation of a sharp boundary, this enables the fringes to be identified with certainty.
Kerr effect study of the aqueous solutions of three globular proteins
Authors: Riddiford C. L. , Jennings B. R. 
Published: December 2004

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, w at 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 strong electric fields.
Effect of binding on melting transitions in polymer–diluent systems
Authors: Orofino T. A. , Ciferri A. , Hermans J. J. 
Published: December 2004

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 not necessarily true.
Calculated optical properties of 64 trinucleoside diphosphates
Authors: Cantor Charles R. , Tinoco Ignacio 
Published: December 2004

AbstractThe optical rotatory dispersion and ultraviolet absorption spectra of the 64 trinucleoside diphosphates containing the bases A, U, C, and G have been calculated by using a simple semiempirical approach. These calculations accurately predict the optical properties of the nine trimers for which extensive experimental results are available. The computed optical data should be useful in the identification of oligonucleotides obtained in the course of sequence determination of ribonucleic acids and should simplify the determination of the concentration of oligonucleotides in aqueous solution. Additional calculations indicate that it should be possible to analyze most, mixtures of sequence isomers of trinucleoside diphosphates by direct, measurement of the ORD of the mixture at neutral pH.
Thermal transition of DNA measured by NMR spin‐echo technique
Authors: Lubas Barbara , Wilczok Tadeusz , K.‐Daszkiewicz Olgierd 
Published: December 2004

AbstractThe thermal helix–coil transition of DNA can be studied by means of the spin‐echo technique. The longitudinal spin–lattice relaxation time T1 and the transvense spin–spin relaxation time T2 of the DNA sample show a similar phase transition as observed spec‐trophotometrically with increasing and decreasing temperatures. Four slopes on the T1 and T2 temperature relationship curves were found and interpreted as functions of nonrelational hydration of the DNA molecule. The T1 and T2 values differ depending on the native or denatured state of the DNA molecule. The importance of the dynamic equilibrium between water molecules in the hydration lattice and steps in the denaturation of the DNA molecule are discussed. This phenomenon may be directly related to the nonrotational hydration.
Sedimentation coefficient of polyoma virus DNA
Authors: Gray Horace B. 
Published: December 2004

AbstractThe sedimentation coefficient of the twisted circular form of polyoma virus DNA is calculated from the Kirkwood sedimentation–diffusion equation, the structure being assumed to be a rigid double superhelix. Agreement with the experimental sedimentation coefficient can be obtained, with the use of an experimental value for the number of superhelical turns, when the pitch of the superhelix is intermediate between its minimal and maximal possible values. Another model, which has been proposed for polyoma DNA at low ionic strengths, may be visualized as a superhelical structure wound about a torus. Calculations of sedimentation coefficients for this model agree qualitatively with experimental data at ionic strengths Below 10−2M.
Kinetics of biopolymerization on nucleic acid templates
Authors: MacDonald Carolyn T. , Gibbs Julian H. , Pipkin Allen C. 
Published: December 2004

AbstractThe kinetics of biopolymerization on nucleic acid templates is discussed. The model introduced allows for the simultaneous synthesis of several chains, of a given type, on a common template, e.g., the polyribosome situation. Each growth center [growing chain end plus enzyme(s)] moves one template site at a time, but blocks L adjacent sites. Solutions are found for the probability nj(t) that a template has a growing center that occupies the sites j — L + 1,…, j at time t. Two special sets of solutions are considered, the uniform‐density solutions, for which nj(t) = n, and the more general steady‐state solutions, for which dnj(t)/dt = 0. In the uniform‐density case, there is an upper bound to the range of rates of polymerization that can occur. Corresponding to this maximum rate, there is one uniform solution. For a polymerization rate less than this maximum, there are two uniform solutions that give the same rate. In the steady‐state case, only L = 1 is discussed. For a steady‐state polymerization rate less than the maximum uniform‐density rate, the steady‐state solutions consist of either one or two regions of nearly uniform density, with the density value(s) assumed in the uniform region(s) being either or both of the uniform‐density solutions corresponding to that polymerization rate. For a steady‐state polymerization rate equal to or slightly larger than the maximum uniform‐density rate, the steady‐state solutions are nearly uniform to the single uniform‐density solution for the maximum rate. The boundary conditions (rate of initiation and rate, of release of completed chains from the template) govern the choice among the possible solutions, i.e., determine the region(s) of uniformity and the value(s) assumed in the uniform region(s).
Vacuum ultraviolet absorption spectra of sublimed films of nucleic acid bases
Authors: Yamada Takenori , Fukutome Hideo 
Published: December 2004

AbstractMeasurements of the optical absorption spectra of the sublimed films of adenine, guanine, cytosine, thymine, and uracil were extended down to 120 mμ at room temperature. Several remarkable absorption peaks were found to exist below 190 mμ in addition to the already known ones near 260 mμ and 200 mμ. The intensities of these peaks were comparable to or, in some cases, even larger than those near 260 mμ and 200 mμ. It was found that the relative intensities of the absorption peaks differed considerably from sample to sample for all five bases, probably due to variation in the arrangement of the bases in the sublimed films. It was found also that the absorption spectra of the sublimed films change with aging on standing in vacuo at room temperature. On comparing the spectra of several fresh samples it was found that the intensities of the transitions with wavelength longer than 160 mμ of adenine, guanine, and uracil films are inversely correlated with those of the transitions shorter than 160mμ.
A theory on the effect of low molecular salts on the conformation of linear polyions
Authors: Oosawa Fumio 
Published: December 2004

AbstractThe effect of low molecular salts on the conformation of linear polyions is analyzed on the basis of the additivity law for the thermodynamic properties of polyelectrolytes in the presence of salts. In the case of flexible polyions the theory shows that the logarithm of the conformation parameter changes proportional to A ln (1 + γs0Cs/γpCp) as a function of the salt concentration cs, where cp is the concentration of counterions from polyelectrolytes and γp and γs0 are the activity coefficient of counterions from polyelectrolytes in the absence of salts and from salts in the absence of polyelectrolytes, respectively. In the case of the discontinuous transition of the conformation of polyions, it is shown that the change of the transition point by salts is proportional to the same factor as the above. The constant A, which determines the magnitude of the effect of salts, is proportional to the sensitivity of the activity coefficient to the conformation of polyions in the absence of salts. A similar analysis is made for the conformational change due to dilution by the addition of solvent. These theoretical results are found to be in good agreement with experimental data on the viscosity of flexible polyions and on the helix–coil transition of biopolymers. The interrelation between these conformational changes and various thermodynamic properties of polyelectrolytes with salts is discussed.
Acid–base behavior of poly (vinylpyrrolidone–vinylimidazole) copolymers
Authors: Klotz Irving M. , Lyndrup Mark L. 
Published: December 2004

AbstractCopolymers of vinylimidazole and vinylpyrrolidone containing 0.7–24% of the former residue have been prepared. Titration behavior was examined over a range of temperature and at several ionic strengths. Intrinsic pK's, corrected for electrostatic effects, arc independent of mole fraction of imidazole residue in the copolymer. Nevertheless they are about 1.15 pK units lower than in the corresponding model small molecule, N‐ethylimidazole. Enthalpies and entropies of ionization in the copolymer are changed by ionic strength. It is apparent that the charged state of an N‐ethylimidazole residue placed in a macromolecular matrix is destabilized relative to the uncharged state because of changes in the local polymer or solvent environment.
Esterolytic activity of vinylimidazole–vinylpyrrolidinone copolymers
Authors: Kopple Kenneth D. 
Published: December 2004

AbstractCopolymers of vinylimidazoles and vinylpyrrolidinone, dilute in imidazole residues, have been prepared; their reactivity in the hydrolysis of p‐nitrophenyl acetate has been examined. The catalytic activity of imidazole residues in these copolymers is comparable to that of nonpolyineric imidazoles of the same basicity, and no kinetic effects of preassociation of polymer with substrate ester of p‐nitrophenol were detected. It is suggested that although polyvinylpyrrolidinone probably does bind these substances, they are sequestered from the catalytic, side chains.
Stereochemical criteria for polypeptides and proteins. V. Conformation of a system of three linked peptide units
Authors: Venkatachalam C. M. 
Published: December 2004

AbstractThe general conformations of a system of three linked peptide units are studied, and it is found that there are three types of conformations which contain NH…O hydrogen bonding between the first and the third units. One of them is part of a 310‐helix, while the other two arc nonhelical. The two nonhelical conformations are very similar, and in both the cases the peptide chain turns around, reversing the direction of progress. Such a conformation can therefore occur in the region where a polypeptide chain folds back on itself, as in the cross‐β structure. The method of representing these interesting tripeptide conformations in a (ϕ,ψ) map is described. Examples of such hydrogen‐bonded, nonhelical conformations which occur in peptides and proteins are discussed—e.g., in cyclohexaglyeyl, an open tetrapeptide Gly‐L‐Pro‐L‐Leu‐Gly, and in parts of the lysozyme chain.
Gel–water relationships: Dielectric dispersion
Authors: Masuzawa Mitsunobu , Sterling Clarence 
Published: December 2004

AbstractAt low frequencies, the dielectric constant of gels of agar, carboxymethyl cellulose, gelatin, mid maize starch is much higher than that of water. It decreases continuously as the frequency increases, tending to level off at about 108 cps. The dielectric constant is lower the higher the concentration of polymer; it increases in the order: carboxymethyl cellulose, agar, starch, and gelatin. Results are most reasonably explained by assuming a more solid structure of water the lower the dielectric constant.
Studies on conformational changes in the DNA structure induced by protonation: Reversible and irreversible acid titrations and sedimentation measurements
Authors: Zimmer Ch. , Triebel H. 
Published: December 2004

AbstractReversible and irreversible conformational changes in the acid‐induced denaturation of DNA were studied by spectrophotometric titration, sedimentation, and melting measurements. A GC‐rich DNA (72 mole‐%) shows complete or partial reversibility of the titration profiles within the pH region of transition from helix to coil, while AT‐rich DNA (29 mole‐%) is irreversible in its titration behavior at each acid pH below the onset of the transition. The results for GC‐rich DNA further indicate distinct differences in the titration behavior, which can be attributed to differences in the frequency of GC clusters along the DNA molecule. Plots of the sedimentation coefficient and the parameter asapp against pH lead to the conclusion that conformational changes occur before the onset of the acid‐induced helix–coil transition. These alterations are more pronounced upon protonation of larger GC‐rich domains than of smaller ones, as concluded from very marked differences observed in the sedimentation–pH behavior of two GC‐rich DNA's. An acid denaturation scheme for a GC‐rich DNA segment is suggested. Reversibility of the acid denaturation is explained by the existence of stable, protonated, single GC base pairs in nonprotonated stacked single‐stranded domains formed in the acid‐induced transition region.