bluuebunny/crossref_metadata_2025_split huggingface dataset:
Studies of polypeptide structure by fluorescence techniques. III. Interaction between dye and macromolecule in fluorescent conjugates
Authors: Gill Thomas J. , McLaughlin E. M. , Omenn Gilbert S. 
Published: December 2004

AbstractThe effects of pH on the polarization of fluorescence of dyes dissolved in media of high viscosity or conjugated to polypeptides that undergo no structural transitions indicate that DNS is useful for studying pH‐dependent molecular transition over the range pH 2.5–14, whereas fluorescein is useful only over the range pH 6–8. Heating and cooling in aqueous solutions cause no change in the polarization of fluorescein or of DNS; therefore, the dyes themselves do not introduce artifacts into heating studies of the dye conjugates. The interaction between fluorescein or DNS and the molecule to which it is conjugated varies and thus may affect the measurements made with the conjugates: the rotational relaxation times of polylysine, of a copolymer of glutamic acid and lysine, and of lysozyme are approximately twice as long when measured with DNS‐conjugates as when measured with fluorescein‐conjugates. The explanation for this observation is postulated to lie in the tighter binding between fluorescein and the molecule to which it is conjugated, presumably around the point of its covalent attachment, which makes it a better indicator of the behavior of the rotational kinetic unit of the polypeptide chain. The stronger binding of fluorescein is inferred from two lines of evidence: (1) the fluorescent intensity and ultraviolet spectra of a fluorescein–polylysine conjugate are less susceptible to changes in solvent than those of the DNS conjugate, and (2) the net charge of the polypeptide affects the ionization of fluorescein much less than it affects the ionization of DNS. Additional evidence from previous studies corroborates this conclusion. Thus, it is important to establish the relationship between the fluorescent dye and the molecule to which it is conjugated before using the fluorescence data to calculate rotational relaxation times and other molecular parameters.
Synthèse et structure de la poly‐O‐carbobenzoxy L‐ tyrosine et de copolymères de O‐carbobenzoxy L‐tyrosine et de glutamate de benzyle ou d'aspartate de benzyle
Authors: Vollmer Jean‐Pierre , Spach Gérard 
Published: December 2004

AbstractThe optical rotatory dispersion of copolymers of O‐carbobenzoxy‐L‐tyrosine and benzyl L (or D)‐glutamate as well as benzyl L‐aspartate, dissolved in nonpolar solvent, has been studied. Moffitt's equation permits the determination of b0 coefficients whose variation, with varying composition in amino acid residues, suggests that the molecules of poly‐O‐carbobenzoxy‐L‐tyrosine have a helical structure similar to that of poly‐(benzyl L‐glutamate). Results obtained from infrared spectroscopy and x‐ray diffraction show that the copolymers possess a helical conformation in the solid state, even when they are very rich in carbobenzoxy‐L‐tyrosine residues. The value of the b0, coefficient for poly‐O‐carbobenzoxy‐L‐tyrosine may be explained by a regular stacking of the chromophore groups around the helical backbone. The ordering of the molecules of this polymer in a purely helical structure seems favored by the insertion of a small number of foreign residues in the polypeptide chain.
Activity coefficients of counterions in solutions of diethylaminoethyl dextran hydrochloride
Authors: Gubenšek F. , Lapanje S. 
Published: December 2004

AbstractActivity coefficients of counterions in solutions of diethylaminoethyl dextran hydrochloride have been determined. It has been observed that they increase with decreasing concentration of the polyelectrolyte. The experimental values have been compared with those calculated using Oosawa's theory of activity coefficients. The calculated values are higher than those observed, which suggests that the rodlike model on which Oosawa's theory is based is inadequate for the present case. Activity coefficients of counterions of some solutions containing NaCl and KC1, respectively, have also been determined. It has been found that the additivity rule for activity of counterions applies for these solutions.
NMR and optical activity observations on the helix–coil transition in poly(γ‐benzyl L‐glutamate) solutions
Authors: Liu Kang‐Jen , Lignowski J. S. , Ullman Robert 
Published: December 2004

AbstractThe helix–coil transition of poly(γ‐benzyl L‐glutamate) was studied by comparing proton magnetic relaxation behavior with optical activity studies. The transition temperature as determined by magnetic relaxation was lower than that obtained by optical activity. The concentration dependence of the transition was also studied. The relationship of these experiments with previous NMR studies and also with calorimetric investigation of the transition is developed.
Origin of branches in native dextrans
Authors: Ebert K. H. , Brosche M. 
Published: December 2004

AbstractAccording to the proposed mechanism for the enzymatic formation of dextran, branches of different length are formed in a reaction between a so‐called acceptor dextran molecule and an active reaction complex; propagation of the dextran chain occurs by an insertion‐type polymer growth. To investigate this branching reaction, radioactive labeled acceptor dextran of relatively low molecular weight was added to a dextran synthesizing system and the native high molecular weight dextran separated by a fractionation method. From the specific radioactivity of the isolated native dextran, and assuming a molecular weight of 2.5 × 105, the average number of acceptor molecules incorporated into native dextran is calculated to be about unity, as predicted by the proposed mechanism. Analogous results have been obtained in the reaction of two different dextran sucrases from Leuconostoc mesenteroides B512F and B1307, respectively.
Rotatory dispersion of the β‐form of polypeptides
Authors: Volkenstein M. V. , Zubkov V. A. 
Published: December 2004

AbstractThe rotatory dispersion of the β‐form of polypeptides is considered. The parameter b0 of the Moffit‐Yang equation is calculated quantum mechanically. The results obtained b0 = −30, agrees with experiment which gives b0 near zero for the β‐form.
Spectrophotometric titration studies on poly (uridylic acid)
Authors: Simpkins H. , Richards E. G. 
Published: December 2004

AbstractIn order to provide preliminary data for the interpretation of the spectrophotometric titration properties of RNA, the spectral changes accompanying the ionization of poly‐(uridylic acid) have been determined, as have the ionization constants as a function of salt concentration and the enthalpies and entropies of ionization. The spectral propertics and ionization constants of poly (uridylic acid) have been compared with those of 2′(3′) Uridine monophosphate and of uridine; significant, differences have been established. The results obtained are consistent with the hypothesis that uracil residues in poly U are stacked only in concentrated salt solutions.
Experimental thermodynamics of the helix–random coil transition. I. Influence of polymer concentration and solvent composition in the PBG–DCA–EDC system
Authors: Ackermann Theodor , Neumann Eberhard 
Published: December 2004

AbstractThe course of the reversible helix formation of poly(γ‐benzyl L‐glutamate) (PBG) dissolved in a mixture of dichloroacetic acid (DCA) and 1,2‐dichloroethane (EDC) was followed by measuring the heat capacity and the optical rotation of the system through the transition region. The results of these measurements indicate that the transition enthalpy ΔH the transition temperature Tc, and the Zimm‐Bragg parameter σ depend considerably on the PBG concentration as well as on the composition of the solvent. For the standard state of infinite dilution, however, a linear extrapolation of the measured ΔH if values results in a standard value ΔH° = 950 cal./mole, independent of the solvent composition. The results of the calorimetric measurements are discussed in relationship to changes in optical rotation. Some peculiarities in the measured thermodynamic and optical properties in solutions with relatively high content of dichloroacetic acid are reported.
Topography of nucleic acid helices in solutions. II. Structure of the double‐stranded rA–rU, rI–rC, acid rA, and the triple‐stranded rA–rU2 and rA–rI2 helices
Authors: Gabbay Edmonxd J. 
Published: December 2004

AbstractInformation concerning the structures of rA–rU, rA–rU2 rI–rC, rA–rI2, and acid rA helices in solutions is reported. Through the use of diquaternary ammonium salts of the general structure, \documentclass{article}\pagestyle{empty}\begin{document}$ {\rm R}_1 {\rm R}_2 {\rm R}_3 \mathop {\rm N}\limits^ + ({\rm CH}_2 )n\mathop {\rm N}\limits^ + {\rm R}_1 {\rm R}_2 {\rm R}_3 \cdot 2{\rm Br}^ - $\end{document} (I), it is shown that (1) the distances between adjacent negatively charged oxygen atoms on the helix increases in the following order rA–rI2 < rI–rC < rA–rU ⩽ rA–rU2; (2) the density of the helices increases in the order. rA–rI2 < rA–rU < rA–rU2 < rI–rC; (3) there is a large hydrophobia site in rA–rI2 and possibly also in rA–rU, rA–rU2, and rI–rC helices; (4) the results of the interactions between the salts of type I and the helices may be formulated in semi‐quantitative terms by the use of two parameters, α, and β which are shown to be related to the charge separation and the density of the helices, respectively; (5) the studies in solutions compare favorably with the x‐ray studies on the fibers; and (6) the acid rA helix differs significantly from the other helices by the fact that the electrostatic interstrand interactions between the negatively charged oxygen atom of a phosphate group and the positively charged 10‐amino group of adenine contribute significantly to the stabilization of the helix, and thus it is found that the presence of the salts, I, leads to a significant destabilization of the acid rA helix.
Conformational analysis of poly‐N‐methyl‐L‐alanine
Authors: Liquori A. M. , De Santis P. 
Published: December 2004

AbstractSterically allowed forms of the poly‐N‐methyl‐L‐alanine chain were found by calculation of conformational energies as a function of the rotation angles of its chain bonds. The lowest energy form seems to be a right‐handed, approximately threefold helix.
X‐Ray diffraction of oriented amylose fibers. II. Structure of V amyloses
Authors: Zobel H. F. , French A. D. , Hinkle M. E. 
Published: December 2004

AbstractOriented amylose fibers in the V form were prepared and subjected to x‐ray analysis. Unit cells and the probable space group of P212121 were determined for the V anhydrous and V hydrate forms of amylose; the analysis confirms previous predictions of these structures based on x‐ray powder patterns. Chain folding in V amyloses is discussed in view of crystallographic evidence and folding experiments conducted with space‐filling models. Reported also is evidence for amylose helices having diameters intermediate between 13.0 and 13.7 A.
Complexing and denaturation of DNA by methylmereuric hydroxide. II. Ultracentrifugation studies
Authors: Gruenwedel Dieter W. , Davidson Norman 
Published: December 2004

AbstractWhen increasing concentrations of methylmercuric hydroxide are added to a Cs2SO4 solution of native DNA, the buoyant density of DNA is unaltered until a critical concentration is reached above which there is a cooperative transition to denatured DNA which now binds so much CH3HgOH that it becomes very dense and nonbuoyant. As increasing concentrations of methylmercuric hydroxide are added to a Cs2So4 solution of denatured DNA, the buoyant density gradually increases, indicating a gradual increase in the amount of methylmercury cation bound. The denatured DNA methylmercury complex becomes nonbuoyant at the same concentration of methylmercuric hydroxide as does the native DNA. These results support our previous interpretation that CH3HgOH reacts with the imino NH bonds of thymine and guanine in nucleic acids. The reaction occurs more or less independently at the different binding sites for denatured DNA, but it occurs cooperatively with simultaneous denaturation for native DNA. The nature of the transition of denatured DNA to the nonbuoyant state is not known, but it is probably due to an abrupt decrease in the degree of hydration of the DNA when its density and hydrophobic character are sufficiently increased by the binding of the methylmercury cation. Direct measurements of the amount of methylmercury bound by DNA, as observed by preparative ultracentrifugation, confirm approximately the buoyant density results as to the amount of methylmercury bound. The possibility of using methylmercuric hydroxide as a reagent for the separation of complementary strands, depending on then thymine of their thymine plus guanine content, is discussed.
Statistical mechanical studies of polypeptides. I. Theory of the helix–coil transition including right and left‐handed helical states
Authors: Scott Roy A. 
Published: December 2004

AbstractThe Lifson‐Roig and Zimm‐Bragg theories of the helix–coil transition in polypeptides are generalized to include both right‐ and left‐handed α‐helical states. The partition functions for these more general theories are formulated in terms of the parameters u, vR, VL, WR, and wL for the generalized Lifson‐Roig theory and σR, σL, sR, and sL for the generalized Zimm‐Bragg theory. Matrix equations are derived for calculating such average molecular properties as the fraction of the amino acid residues hydrogen bonded into right‐ and left‐handed α‐helices, the average number of right‐ and left‐handed helical sequences per molecule, the number‐average length (in residues) of the right‐ and left‐handed helical sequences, and the degree of solvent binding to the peptide NH and CO groups. These equations are shown to be conveniently adaptable to machine methods of calculation, thus avoiding the difficulty of solving an eigenvalue problem where the secular equation is of a high order. A discussion is given of the various energetic and entropic effects which determine the screw sense and stability of helices and of the extent to which it is valid to interpret experimental data by adjustment of the parameters of these statistical mechanical theories which include in their formulation only near‐neighbor interactions between residues.
Electrostatic effects on polynucleotide transitions. I. Behavior at neutral pH
Authors: Record M. Thomas 
Published: December 2004

AbstractAn approximate analytical expression for the electrostatic free energy of a polynucleo‐tide in any of its possible ordered or random conformations is derived by integration of the screened‐Coulomb potential energy function over all charge pairs in the structure. The electrostatic free energy of any form is found to be a linear function of the logarithm of the monovalent counterion concentration, in the range of low salt concentrations. Hence the electrostatic free energy difference between ordered and disordered forms in a polynucleotide structural transition is a linear function of the logarithm of the monovalent counterion concentration. A free energy balance applied to a two‐state model for the transition then yields a linear dependence of the transition temperature Tm upon the logarithm of the counterion concentration. Calculation of the quantity dTm/d log M, where M is the monovalent counterion concentration, shows it to be a characteristic constant for a given transition, with a magnitude and sign proportional to the charge density difference between the ordered and disordered forms. Use of any one of several alternate, simple assumptions yields predicted dTm/d log M values in good agreement with experimental data for various polynucleotide transitions.
Numerical solutions of the Lamm equation. IV. Rotor slowing experiments
Authors: Billick Irwin H. , Dishon Menachem , Weiss George H. , Yphantis David A. 
Published: December 2004

AbstractThis paper presents the results of a numerical solution of the Lamm equation for roton slowing specified by ω2 = ω02 exp {– λτ}, for parameters relevant to equilibrium experiments. It. is shown that in the two‐component system it is theoretically possible to deduce s/D from measurements of the difference of concentration across the. cell with rotor slowing, provided that the time at which the difference reaches a maximum is known.
Effect of carcinogens and related compounds on the semiconductive properties of protein
Authors: Snart Ronald S. 
Published: December 2004

AbstractThe d.c. electrical conductivity of solid gels of bovine plasma albumin, under high vacuum, shows a semiconductive behavior which is sensitive to small amounts of complexed carcinogens and related compounds. The effect of these compounds on the electrical properties of the protein provides evidence of an interaction which may be related to the carcinogenic activity.
Electrophoresis of absorbed RNA
Authors: Chowrashi P. K. , Chattoraj D. K. , Chakravarti K. 
Published: December 2004

AbstractThe electrophoretic mobilities of adsorbed yeast ribonucleic acid have been measured as functions of pH, ionic strength, and biopolymer concentration and the results so obtained have been critically compared with those for adsorbed DNA. Like DNA, ribonucleic acid has also been found to reverse the positive charge of alumina owing to its adsorption on the solid‐liquid interface. The mobilities of adsorbed RNA have been found to be less than those of adsorbed DNA under identical conditions. The observed mobilities of adsorbed heat‐ and alkali‐denatured RNA are significantly less than those of adsorbed native RNA at a given pH and ionic strength of the medium. The electrophoretic mobilities as observed also show the evidence of RNA adsorption on the negatively charged surface of Dowex‐50 resin, but practically no adsorption of RNA on the negatively charged glass surface has been predicted.
Flow birefringence of T2 bacteriophage DNA
Authors: Harrington Rodney E. 
Published: December 2004

AbstractThe streaming birefringence and extinction angles of DNA from T2 bacteriophage in neutral aqueous buffers have been determined over a range of concentrations from 5 to 44 μg./ml. and of velocity gradients from 5 to 50 sec.−1. Although the extinction angles are relatively small even at the lowest velocity gradients and concentrations studied, a lower limit estimate of the limiting extinction angle to shear rate ratio can be made, and this value is interpreted in terms of available dynamical theory. The statistical segment length has been estimated from the birefringence data as ∼ 1100 A. This figure is in satisfactory agreement with the results of independent calculations by others.
Calculation of melting curves for DNA
Authors: Crothers Donald M. 
Published: December 2004

AbstractA method is reported for calculating the melting curve of a DNA molecule of random base sequence, including in the formalism the dependence of the free energy of base pair formation on the size of a denatured section. Some explicit results are shown for a “typical” base sequence, in particular the probability of helix formation at individual base pairs in several different regions of the molecule and the amount of melting from the end of the chain. Particular attention is drawn to the variation of local melting behavior from one region of the molecule to another. It is found that sections rich in AT melt at relatively low temperatures with a fairly broad transition curve, whereas regions rich in GC pairs melt at higher temperatures (as expected) with a very abrupt, local transition curve. To account qualitatively for the results one may divide melting into two kinds of processes: (a) the nucleation and growth of denatured regions, and (b) the merging together of two denatured sections at the expense of the intervening helix. The first of these processes dominates in the first stages of melting, and leads to rather broad local melting curves, whereas the second process predominates in the later stages, and occurs, in a particular part of the molecule, over a very narrow temperature range. It is estimated that the average length of a helix plus adjacent coil section at the midpoint of the transition is approximately 600 base pairs. Since transition curves which measure the local melting behavior reflect local compositions fluctuations, these curves contain information about the broad outlines of base sequence in the molecule. Some suggestions are made concerning experiments by which this potential information source could be exploited. In particular, it is pointed out that one might hope to map AT or GC rich regions at particular genetic loci in a biologically active DNA molecule. Values of the relevant parameters found earlier for the transition of homopolymers produce melting curves for a DNA of random base sequence which are in good agreement with the experimental transition curve for T2 phage DNA. Hence the present theoretical picture of the melting of polynucleotides is at least internally self‐consistent.
Optical anisotropy of synthetic polynucleotides. I. Flow birefringence and π‐electron polarizabilily of bases
Authors: Takashima Shiro 
Published: December 2004

AbstractBirefringence of poly‐A, poly‐U, and double‐stranded poly‐AU are investigated experimentally as well as theoretically. Single‐stranded poly‐A, at low ionic strength, exhibits a strong negative birefringence indicating that, adenine molecules are stacked regularly with their planes along the transverse direction. On the addition of Mg or Mn ions, the birefringence decreases markedly. Poly‐U has no noticeable birefringence indicating that poly‐U has a contracted configuration in solution. On mixing poly‐A and poly‐U with 10–3M MgCl2, the birefringence increases markedly, but the change in the chain configuration seems less pronounced. The polarizability of adenine and uracyl are ejaculated using the simple Ifïückel scheme. The calculation shows that the π‐electron polarizability normal to the base plane is zero. Therefore, the negative birefringence is probably due to the lack of π‐electron polarizability in the direction normal to the base plane and accordingly no π‐electron polarizability along the major helix axis. Conversely, the negative birefringence is an indiaction of base stacking.
Determination of stability of the DNA double helix in an aqueous medium
Authors: Privalov P. L. , Ptitsyn O. B. , Birshtein T. M. 
Published: December 2004

AbstractThe possibility of determining the free energy of stabilization ΔG0 of native DNA structure with the help of calorimetric data on heats ΔH of transition from the native to denaturated state is considered. Results of microcalorimetric measurements of heats of denaturation of T2 phage DNA at, different values of pH and ionic strength of solution are given. Values of free energy of stabilization of the DNA native structure ΔG0 under various conditions have been obtained. It is shown that under conditions close to physiological ΔG0 approaches 1200 cal/mole per base pair.
Poly(L‐leucyl‐L‐ornithyl‐L‐leucine) and its Guanidization Product: Synthesis and Antibacterial Activity
Authors: Fridkin M. , Frenkel A. , Ariely S. 
Published: December 2004

AbstractThe synthesis of poly(L‐leucyl‐L‐ornithyl‐L‐leucine) and of poly(L‐leucyl‐L‐arginyl‐L‐leucine) is reported. The antibacterial action of the two copolymers was checked by growth inhibition experiments on Staphylococcus aureus. The activity was found to be identical with that of a disordered 1:1 copolymer of L‐ornithine and L‐leucine. Conversion of 75% of the ornithine residues to arginine had no effect on the antibacterial activity.