bluuebunny/crossref_metadata_2025_split huggingface dataset:
Hydrophobic interaction and a model for the elasticity of elastin
Authors: Gosline John M. 
Published: December 2004

AbstractThe thermodynamics of the elastic process in the rubberlike protein elastin have been investigated by microcalorimetery. The results indicate that the reversible heat liberated upon the extension of water‐swollen elastin at room temperature is much largerthan the stored elastic energy, indicating a large than the stored elastic energy, indicating a large, negative internal energy change for stretching. The ratio of the measured internal energy change to the stored energy varies inversely wiht extension, and at 22° C it is −91 for 2% extension and −3 for 70% extension. The interanl energy change also varies dramatically with temperature over the range of 2–65° C it is zero.The temperature dependence for internal energy change is virtually identical to the temperature dependence for internal energy changes associated with the breaking of hydrophobic interactions, and it is suggested that the measured internal energy change can be attributed entirely to hte absorption of water onto nonpolar groups in the elastin network. Calculatons based on this assumption indicate that the free‐energy change associated with this solvent–polymer process is large and positive. It is concluded that the absorption of water onto hydrophobic groups contributes to the elasticity of elastin, particularly at extensions of less than about 70%. The implications of this elastic mechanism are discussed in terms of the random‐network model for elastin structure.
Conformational studies of bacterial polysaccharides. II. Optical activity of some bacterial capsular polysaccharides
Authors: Wolf Ch. , Elsässer‐Beile U. , Stirm S. , Sutton G. G. S. , Burchard W. 
Published: December 2004

AbstractThe optical activity of the Klebsiella capsular polysaccharides of serotypes K1, K5, K6, K8, K11, K56, and K57 has been studied in aqueous solution. Measurements of ORD in the range 185–450 nm reveal anomalous ORD with Cotton effects near λ0 = 195nm. The results are evaluated quantitatively according to hte Moffitt‐Yang and the Drude equations. Straight lines are obtained in the Moffitt‐Yang plots, while the corresponding Drude plots yield bent curves. The b0 values, calculated from the slope of the stright lines in the Moffitt‐Yang plot, range from 90 to 270 and suggest a helical superstructure for the capsular polysaccyharides. Positive b0 values have been found for K1, K5, and K6 and negative b0 values for K8, k11, K56, ad K57. Circular dichrosim has been mesured, but the CD curves are found to be truncated at the lower‐wavelength end due to the 185‐nm limit of the spectrometer used. Measurements of the temperature dependence of the specific optical rotation [α] reveal in all cases cooperative order–disorder transitions at temperatures, Tm, fro m298 to 323°K. The van′t Hoff enthalpies derived from the width of the transition curves are found to be similar in value to those of polypeptieds in aqueous solution. The K8 polysaccharide shows a two‐step transition. The results are discussed in relation to the known primary structure and x‐ray data from oriented and partially crystalline films. A model is suggested for the two‐step transition in the K8 polysaccharide.
Dynamic structure of polyriboguanylic acid in neutral aqueous solution. A proton and phosphorus‐31 NMR study
Authors: Yamada Atsuko , Akasaka Kazuyuki , Hatano Hiroyuki 
Published: December 2004

AbstractAn NH proton signal was observed in neutal D2 solution (pH 5.8 ± 0.2) of poly (G) (Mr > 150,000) that had been lyophilized from H2O. This NH proton is slowly exchanged with deuterium with a rate constant of 5 × 10−5 sec−1 at 29.5° C. This proves that poly(G) exists in a relatively rigid multistranded form after lyophilization in neutral aqueous solution. The number of NH protons, observedis approximately 0.5 per nucleotide, indicating that this multistrand would not be a complete four‐stranded form as suggested by x‐ray works [Zimmerman et al. (1975) J. Mol. Biol. 92, 181–192: and Arnot et al. (1974) Biochem. J. 141, 537–543]. The large difference between phosphorus‐31 spin–spin relaxation time (T2) measured with the spin‐echo method and that calculated from the line width suggests that there is a distribution of rotational angles about the phosphodiester bond. The rate of conversion among different conformatonal states is slow in the nmr time scale and is estimated to be less than 300 sec−1 at 28° C.For both phosphorus and H8 proton, spin‐‐lattice relaxation time (T1) and T2 show opposite temperature dependence and the ratio of T1 to T2 gives the correlation time τr of 5 × 10−8 sec and 7 × 10−8 sec (at 27° C) for H8 and phosphorus, respectively. These correlation times are considerd to represent the slow rotional diffusion of the multistranded form of poly(G).
Dilute solution properties of proteoglycan fractions from bovine nasal cartilage
Authors: Kitchen Robert G. , Cleland Robert L. 
Published: December 2004

AbstractFresh proteogycans (adult bovine nasal cartilage) isolated from the densest portion of a dissociative density gradient had a weight‐average molecular weight of ca. 106 in 4M guanidine hydrochloride (GdnHCI) by light scattering. Fractions of such material obtained by elution with 4M GdnHCI from 2% agarose gel, both normal and cross‐linkd, has proteoglycan subunit molecular weights ranging from 0.8 to 2.6 × 106 and root‐mean‐square radii ranging from 35 to 52 nm in the same solvent. The protein molecular weight per proteoglycan subunit was about 1.2 × 105 and that of keratan sulfate about 1.8 × 105, both independent of total molecular weight. A random‐flight “graft copolymer” model having uniform side chains of chondroitin sulfate (40 disaccharides) and keratan sulfate (15 disaccharides) and a random‐coil polypeptide back bone was used to estimate the unperturbed radius, whihc was about 19 nm for a mol wt of 1.5 × 106. Experimental light‐scattering data for fractions were fitted very well by theoretical curves for the particale scattering factor for both linear and appropriate branched polymers. Examination of coil expansion on the basis of perturbation calculations for branched polymer models suggested that expansion did not account for the experimentally observed radii in terms of unperturbed radii calculated from the model. A possible explanation is that substantial local stiffening of the polypeptide chain due to substitution of side‐chain clusters increases the unperturbed radii. The intrinsic viscosity [η] is 4M GdnHCI ranged from 120 to 180 ml/g, and could be interpreted in terms of th eequivalent sphere model; the Flory number has approximately its normal value for flexible linear polymers. The treatment of the sedimentation coefficient by this is less successful, since the Man delkern‐Flory parameter β apparently increases with increasing molecular weight; average value are similar to those for flexible polymers, but the variation in β makes this method useful only for rough estimation of molecular weight of proteoglycans. Molecular weights of purified proteoglycans are the same in 0.2M NaCI as in 4M GdnHCI, while crude preparations gave higher molecular weights in 0.2M NaCI, probably because of association due to incomplete removel of “linking” proteins.
Kinetics of large‐ligand binding to one‐dimensional lattices: theory of irreversible binding
Authors: Epstein Irving R. 
Published: December 2004

AbstractExact solutions are obtained for the time dependence of the extent of irreversible binding of ligands that cover more than one lattice site to a homogeneous one‐dimensional lattice. The binding may be cooperative or noncooperative and the lattice either finite or infinite. Although the form of the solution is most convenient when the ligand concentration is buffered, exact numerical or approximate analytical solutions, including upper and lower bounds, can be derived for the case of variable ligand concentration as well. The physical reason behind the relative simplicity of the kinetics of irreversible as opposed to reversible binding in such systems is discussed.
Degree of polymerization and polydispersity of xylan from the cell wall of the green seaweed Penicillus dumetosus
Authors: Mackie W. , Sellen D. B. 
Published: December 2004

AbstractXylan was extracted from the cell wall of green seaweed penicillus domutosus using a very mild procedure. Xylan dinitrate samples were prepared and their degrees of polymerization found to depend markedly on temperature, of nitration, the best compromise between yield and degradation being at about −20°C. Two samples, one obtained under optimum conditions and one highly degraded, were investigated in detail by using light‐scattering, osmometry, gel‐permeation chromatography, and viscosity techniques. The results show that there are xylan chains present, in the cell wall having degrees of polymerization above 10,000. This figure is much higher than those previously found for other similar xylans. The light‐scattering results show that the xylan dinitrate molecule is much smaller than the molecules of the trinitrates of other structural polysaccharides (cellulose and mannan) for the same degree of polymerization. The effective bond length b is 16 Å, assuming a linear chain.
A proton magnetic resonance study of the interaction of adenylyl (3′ → 5′) adenosine with polyuridylic acid
Authors: Kreishman George P. , Chan Sunney I. 
Published: December 2004

AbstractThe interaction of adenylyl (3′ → 5′) adenosine (ApA) with polyuridylic acid in D2O solution at neutral pD has been studied by high resolution proton magnetic, resonance spectroscopy. At temperatures above ∼32°C, no evidence was obtained for the interaction of ApA with poly U. Below this temperature, a rigid triple‐stranded complex involving a stoichiometry of 1 adenine to 2 uracil bases is formed, presumably via specific adenine–uracil base‐pairing and cooperative base stacking of the adenine bases in a manner similar to that previously reported for the adenosine–poly U complex.
Syntheses of poly[β‐(l)‐menthyl D‐ and L‐aspartates] and their secondary structures
Authors: Yamamoto Hiroyuki , Hayakawa Tadao 
Published: December 2004

Abstractβ‐(l)‐Menthyl D‐ and L‐aspartates were prepared by a fusion reaction of N‐phthalyl D‐ and L‐aspartic anhydrides with l‐menthol, followed by hydrazinolysis. The monomers were then polymerized to poly[β‐(l)‐menthyl D‐ and L‐aspartates] by the N‐carboxyanhydride method. These polymers were soluble in many organic solvents, such as diethyl ether, tetrahydrofuran, chloroform, n‐bexane, and dioxane. From the results obtained by a study of the optical rotatory dispersions and circular dichroisms, poly [β‐(l)‐menthyl D‐aspartate] was found to be a β form structure in solution. On the other hand, poly[β‐(l)‐menthyl L‐aspartate] was a random‐coil structure. These results suggest that the asymmetry of the l‐menthyl chromophore in the side chain interacts with the polypeptide main chain and causes an extraordinary optical rotation.
Helix–coil transition in copolypeptides. II. Poly(γ‐benzyl L‐glutamate‐co‐ε‐carbobenzoxy‐L‐lysine)
Authors: Roig A. , Blanco F. García , Cortijo M. 
Published: December 2004

AbstractThe thermal helix–coil transition of poly(γ‐benzyl L‐glutamate‐co‐ε‐carbobenzoxy‐L‐lysine) copolypeptides was studied in solvent mixtures of different compositions. The cooperativity parameter v changes linearly with polymer (and solvent) composition, whereas the heat of the transition shows a very pronounced minimum as a function of polymer composition. This minimum cannot be due only or mainly to the solvent changes and must be attributed to the effect on the transition of the side chains of the polypeptides.
Optico‐hydrodynamic properties of high molecular weight DNA. II. Effect of aqueous glycerol solvents
Authors: Harrington Rodney E. 
Published: December 2004

AbstractThe optical and hydrodynamic properties of T2 bacteriophage DNA have been determined by steady‐state flow birefringence and viscosity in glycerol–aqueous buffer solvents at 25°C. Flow birefringence and extinction angle data were obtained over a velocity gradient range of 0.1 to 5 sec−1 and at concentrations from 3 to 55 μg/ml in solvents containing approximately 30, 42, and 48 vol‐% glycerol. Large optical backgrounds were observed in the mixed solvent flow birefringence studies which presented special experimental difficulties; these are described and their effect upon the flow birefringence data are discussed. The data on extinction angle provide no evidence for an internal viscosity effect on the stationary‐state hydrodynamic properties of high molecular weight DNA over a range of solvent viscosity from 0.9 to 4.6 cP. Both the optical and hydrodynamic properties under present conditions of measurement appear to be self‐consistent in terms of the values for these quantities in neutral aqueous buffer solution. Interpretation of the birefringence is complicated by uncertainties inherent in calculating the form anisotropy of DNA in non‐aqueous solvents, but the data imply no large changes in helical structure with increasing glycerol concentration. Both intact and slightly degraded DNA samples were investigated, and no significant polydispersity effects were observed under the experimental conditions described.
Potentiometric and circular dichroic measurements of poly(L‐glutamic acid) in aqueous solutions of organic and inorganic electrolytes at ambient temperature
Authors: Steigman Joseph , Cosani Alessandro 
Published: December 2004

AbstractTitration of an aqueous solution of sodium poly‐L‐glutamate with a strong acid usually produces turbidity and precipitation before the equivalence point is reached. In 1M sodium p‐toluenesulfonate and 1M sodium methylcyclohexanesulfonate aggregation was delayed for days to months. In very concentrated tetra‐n‐butylammonium chloride and bromide the polymeric acid dissolved and could be titrated with NaOH. However, potentiometric titration curves in these solutions did not yield information (by way of plots of apparent pK versus the degree of neutralization) about the helix‐to‐coil transition of the polymer. It was argued in addition that the apparent pK of a weak polyelectrolyte should not be calculated from titrations in concentrated salt solutions since it is a mixed or composite quantity. It contains not only the effect of the salt on the dissociation of the weak electrolyte but its effect on the activity coefficient of hydrogen ions as well.Circular dichroic spectra were therefore measured a t various degrees of neutralization of poly(L‐glutamic acid) in a number of aqueous salt solutions and mixtures of organic solvents with water. It was found that the undissociated polymer in the concentrated methylcyclohexanesulfonate and quaternary ammonium halide solutions had the spectrum of a right‐handed α helix. The n → π* band at 222 mμ was used as a measure of the fraction of polymer in the helical conformation. The value of − Δε for the undissociated polyacid in these organic electrolyte solutions was 11.4. By means of this value and a number of assumptions, the fraction of helix (fh) as a function of α, the degree of polyacid neutralization, was calculated for the different solvent mixtures. An empirical equation was used to describe the variation of fh with α, fh = 1/(1 + e−a+bα), in which b represents the degree of cooperativeness of the transition, and a is a measure of the effect of the medium on the onset of the transition. The values of b did not differ very much from one another, suggesting that the cooperativeness of the transition was not sensitive to changes in the medium. On the other hand, the value of a (or its equivalent, the value of α at the halfway point in the transition) was more dependent on the solvent. Comparisons of these results with those of some other workers were made by means of the empirical equation.
Amylose optical rotation in some mixed solvent systems
Authors: Dintzis F. R. , Tobin R. , Babcock G. E. 
Published: December 2004

AbstractThis paper extends a previous study in which a discontinuity in the specific rotation of open chain α‐l,4‐linked glucopyranosides in the water–dimethyl sulfoxide (H2O–DMSO) system was attributed to a symmetry change about a polymer chain segment. Optical rotation of amylose, cyclohexamylose, methyl β‐maltoside, and dextran was measured in the following mixed solvent systems: formamide–dimethyl sulfoxide (F‐DMSO), ethylenediamine–dimethyl sulfoxide (E–DMSO), and hexamethylphosphoramide–dimethyl sulfoxide (HMPA–DMSO). Refractive index measurements were used in an attempt to detect hydrogen bonding between solvent components. The specific rotation of amylose corrected for variation in refractive index (CSR), as a function of solvent composition, showed a discontinuity at solvent compositions corresponding to about 1 mole F to 2 moles DMSO and to 1 mole E to at least 8 moles DMSO. A discontinuity in the CSR function of amylose in the H2O‐DMSO mixed solvent that occurs at 25°C is not observed at 70°C. The CSR function of methyl‐β‐maltoside exhibits a discontinuity in solvent composition corresponding to mole ratios between 2F–DMSO and 3F–DMSO. Present results indicate that an amylose chain segment may undergo a symmetry change in solvent compositions corresponding to mole ratios between F–DMSO and F–2DMSO. Our CSR measurements of amylose and model compounds in E–DMSO and HMPA–DMSO do not permit us to distinguish between possible changes in amylose chain segment symmetry and solvent interactions that could affect symmetry properties of the glucopyranose ring.
Experimental thermodynamics of the helix–random coil transition. IV. Influence of the base composition of DNA on the transition enthalpy
Authors: Klump H. , Ackermann T. 
Published: December 2004

AbstractThe helix–coil transition of DNA of various base compositions has been followed by measuring the heat capacity and the ultraviolet absorption as a function of temperature through the transition region. The results of these measurements indicate that the transition enthalphy ΔH for a given pH value and salt concentration depends considerably on the base composition of the various DNA samples. The values of the transition enthalpies vary from ΔH = 7.73 kcal/mole base pair (MBP) for 31% GC base pairs to ΔH = 8.52 kcal/MBP for 72% GC base pairs. The results of the heat capacity measurements are discussed in relationship to the theoretical models suggested by various authors. Some peculiarities of the measured heat capacity versus temperature curves are reported. The correlation between these peculiarities and the results of the transcription experiments of DNA is discussed.
Effects of alkali ions on myosin conformation
Authors: Cheung Herbert C. , Cooke Roger 
Published: December 2004

AbstractWe have used two probes to study the effects of alkali ions on the conformation of myosin. One was paramagnetic, the “spin label” N‐(1‐oxyl‐2,2,6,6‐tetramethyl‐4‐piperidinyl)‐maleimide, which binds primarily to SH groups; and the other was fluorescent, l‐anilino‐8‐naphthalenesulfonate, which binds to an apolar niche. The bonding of the spin label to myosin was carried out in 0.6M LiCl, 0.6M NaCl, or 0.6M KCl, and the resulting labeled myosin was studied in the same medium in which the myosin was labeled as well as in other alkali chlorides. The electron paramagnetic resonance spectra of the spin label showed that the structure of myosin in the vicinity of the labeled groups differed in the various salts. The protein surface in the region of the labeled groups restricted the rotational freedom of the spin label more in KCl than in any of the other salts. Although ions are known to influence the properties of myosin, our results show that these ions also effect the molecular structure. The fluorescence of l‐anilino‐8‐naphthalenesulfonate, noncovalently attached to myosin in the presence of alkali chlorides, decreased progressively with increasing size of the cations, again showing the protein structure near the probe attachment to be a function of the cation, in the solvent. Ca2+ quenched the fluorescence of the bound probe, indicating an interaction between Ca2+ and the myosin molecule. The effect of Ca2+ on the fluorescence was greatest in KCl.
Minor nucleosides in RNA: Optical studies of dinucleoside phosphates containing inosine
Authors: Formoso Carl , Tinoco Ignacio 
Published: December 2004

AbstractFrom the study of circular dichroism (CD) spectra and hypochromism we conclude that the dinucleoside phosphates IpA, ApI, and IpI stack, while IpU stacks very little. Studies with various concentrations of IpI in low salt, and 1M NaCl indicate that the stacking geometry of this compound is sensitive to the ionic strength of solution. The CD of poly I is presented and compared to the data for IpI. Little change was found in the CD of poly (G,I) (1 : 1) with change of salt concentration, and we conclude that, unlike Poly I, there is no major structural change. From the CD of poly (G, I), IpI, and GpG, the CD of IpG plus GpI is calculated by using the nearest‐neighbor approximation. From the calculated spectrum, we tentatively conclude that there is stacking in either IpG or GpI or both.
Synthesis and physicochemical properties in aqueous solution of the sequential polypeptide poly(Tyr‐Ala‐Glu)
Authors: Ramachandran Janakramana , Berger Arieh , Katchalski Ephraim 
Published: December 2004

AbstractA polypeptide having the repealing sequence (Tyr‐Ala‐Glu)n was synthesized by the polymerization of the N‐hydroxysuccinimide ester of O‐benzyl‐L‐tyrosyl‐L‐alanyl‐γ‐benzyl‐L‐glutamate, followed by the removal of the benzyl groups by means of hydrogen bromide. The main fraction obtained on gel filtration had an average molecular weight of over 60, 000, corresponding to over 500 amino acid residues per polypcptide chain. The polymer is soluble in water above pH 5.5, and precipitates on lowering the pH. The x‐ray powder photographs show features of an α‐helical structure. The dependence of the ultraviolet absorption spectrum, the optical rotatory dispersion, and the fluorescence of poly(Tyr‐Ala‐Glu) on pH, in salt‐free as well as in salt‐containing aqueous solutions, was compared with the corresponding properties of a copolymer containing equimolar proportions of tyrosine, alanine, and glutamic acid in a random sequence. From these measurements it was concluded that poly(Tyr‐Ala‐Glu ) has a helical con formation at low pH and a random coil conformation at high pH, the transition taking place at pH 6 in the absence of salt and pH II in the presence of salt. Thus, in the range pH 7 to l0. random coil‐to‐helix transition can be achieved by merely increasing the ionic strength. A model is proposed for the structure of the helical poly peptide which accounts for the Stability of the helical conformation by assuming hydrogen bonding between the carboxylate group of the ith glutamic acid residue and the hydroxyl group of the (i + 4 )th tyrosine residue. The complex ORD of helical poly(Tyr‐Ala‐Glu) is explained as being due to a superposition of the ORD of an α‐helix and that of a regular array of phenolic ehroniopholes originating from the immobilization of the aromatic rings in the specific structure of the polymer.