摘要:

AbstractThe size and shape parameters of poly(L‐tyrosine) in dimethyl formamide were investigated with fractionated samples of different molecular weight by small‐angle X‐ray scattering. The molecular weight, the radius of gyration of the molecule as a whole, the radius of gyration of the cross section, the mass per unit length, and the length of helix molecule were determined. The molecular conformations proposed by Applequist and Pao for poly(L‐tyrosine) were compared with the experimental results obtained. It was concluded that poly(L‐tyrosine) exists in a form of the right‐handed α‐helix in dime

ISSN:0006-3525    

DOI:10.1002/bip.1977.360161102

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

年代:1977

数据来源: WILEY

摘要:

AbstractFluorescence of 2‐p‐toluidinylnaphthalene‐6‐sulfonate (TNS) was enhanced in the presence of maltooligosaccharides, amylose, and other α‐glucans. The dependence of relative TNS fluorescence intensity per glucose unit on chain length of oligosaccharides was examined. The values of binding constant and thermodynamic parameters, assuming the 1:1 complex for TNS‐amylose (number‐average degree of polymerization,DPN= 17), were determined by the fluorescence titration. The values of thermodynamic parameters for 1:1 complex formation of TNS‐α‐ and β‐cyclodextrins were also determined and compared with those of TNS‐amylose (DPN= 17). The fluorescence intensity of TNS in the presence of amylose (DPN= 600) decreased by the action of glucoamylase and taka‐amylase A. The fluorescence of TNS‐amylose (DPN= 17) system increased with the increased ionic strength. In the presence of pullulan, TNS fluorescence was also enhanced and decreased by the action of pullulanase. Amylopectin enhanced TNS fluorescence rather more strongly than amylose (DPN= 17) at the same concentration. In the presence of dextran, the fluorescence of TNS was scarcely enhanced. The degree of fluorescence enhancement of TNS in the presence of α‐glucans seems to reflect the structures of α‐glucans in solution, since TNS fluorescence is enhanced in the hydrophobic environment or by the disturban

ISSN:0006-3525    

DOI:10.1002/bip.1977.360161103

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

年代:1977

数据来源: WILEY

摘要:

AbstractWe have used band sedimentation in shallow density gradients of CsCl in the preparative centrifuge to analyze the distribution of sedimentation coefficients present in tritium labelled DNA fromD. melanogastercells. The cells were lysed according to the method of Kavenoff and Zimm to preserve very high molecular weight DNA. Sedimentation measurements have been carried out as a function of speed of centrifugation. The resulting distribution functions have been interpreted with the aid of the Zimm‐Schumaker equation for the speed dependence of the sedimentation coefficient of very high molecular weight DNA. Low‐speed centrifugation (3000 rpm) indicates that DNA molecules from the lysate are evenly distributed over values ofS20,wfrom 0 to 514S. This distribution is very sensitive to changes in speed of centrifugation and is transformed into a bimodal distribution at 12,080 rpm. Analysis of this transformation allows us to postulate that perhaps 55% of the DNA in the lysate may have molecular weights in excess of 40 × 109g/mol. Some of these molecules may also possess a variety of configurations including partially replicated branched struct

ISSN:0006-3525    

DOI:10.1002/bip.1977.360161104

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

年代:1977

数据来源: WILEY

摘要:

AbstractThe association of coenzyme A(CoASH) and glutathione (GSH) with the water‐soluble polymers and their esterolytic reactivities were evaluated through the reaction withp‐nitrophenyl acetate in the presence of cationic polymer micelles: partially laurylated poly(2‐ethyl‐1‐vinylimidazole) and poly(4‐vinylpyridine). The polymer micelles with high lauryl‐group content (more than 12 mol%) markedly accelerated the reaction at very low concentrations of the polymer. Other polymers with no or small lauryl‐group content only slightly enhanced the association and the reaction rate. From the rate‐polymer concentration profiles, the association constants (K) and the rate constants for thiol coenzymes bound to the polymer (k′a,bound) were determined: for polymers with more than 12 mol % lauryl‐group content,KCoASH= 1110–2270M−1,KGSH= 170–503M−1,k′a,boundat pH 8.65 = 142–341M−1sec−1.k′a,boundwere 20–340 times larger than that observed in the absence of the polymer. The logarithm ofk′a,boundwas found to be correlated well with the polymer hydrophobicity, indicating that the hydrophobic environment of the polymer activated the bound thiol anions. On the other hand, the polymer hydrophobicity did

ISSN:0006-3525    

DOI:10.1002/bip.1977.360161105

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

年代:1977

数据来源: WILEY

摘要:

AbstractThe nature of hydrogen bonds formed between carboxylic acid residues and histidine residues in proteins is studied by ir spectroscopy. Poly(glutamic acid) [(Glu)n] is investigated with various monomer N bases. The position of the proton transfer equilibrium OH…︁N ⇌ O−…︁H+N is determined considering the bands of the carboxylic group.It is shown that largely symmetrical double minimum energy surfaces are present in the OH…︁N ⇌ O−…︁H+N bonds when the pKaof the protonated N base is two values larger than that of the carboxylic groups of (Glu)n. Hence OH…︁N ⇌ O−…︁H+N bonds between glutamic and aspartic acid residues and histidine residues in proteins may be easily polarizable proton transfer hydrogen bonds. The polarizability of these bonds is one to two orders of magnitude larger than usual electron polarizabilities; therefore, these bonds strongly interact with their environment.It is demonstrated that water molecules shift these proton transfer equilibria in favor of the polar proton boundary structure. The access of water molecules to such bonds in proteins and therefore the position of this proton transfer equilibrium is dependent on conformation.The amide bands show that (Glu)nis α‐helical with all systems. The only exception is the (Glu)n‐n‐propylamine system. When this system is hydrated (Glu)nis α‐helical, too. When it is dried, however, (Glu)nforms antiparallel β‐structure. This conformational transition, dependent on degree of hydration, is reversible. An excess ofn‐propylamin

ISSN:0006-3525    

DOI:10.1002/bip.1977.360161106

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

年代:1977

数据来源: WILEY

摘要:

AbstractCircular dichroism and absorption and light scattering have been used to study the effect of ethyl alcohol on an aqueous solution of Amphotericin B (“Fungizone”), which is an antifungal heptene. In aqueous solution, light‐scattering studies show that Amphotericin B exists in an aggregated form. The estimated mass of these aggregates is about 2 × 106daltons, representing about 2000 molecules. Since the aggregated form is high molecular weight and scattering, the CD involves probably the differential scattering of right and left polarized light. In aqueous solution, Amphotericin B exhibits a strong dissymetric couplet in CD at the wavelength of the absorption maximum (328 nm). This latter maximum presents a blue shift when compared with the normal absorption in polar organic solvents. In hydroalcoholic solutions, for alcohol concentrations below 35%, the molecular weight of the aggregates is unchanged, while the absorption and CD spectra are modified. For alcohol concentrations greater than 35%, the aggregates mass decreases quickly and becomes undetectable at 50% ethyl alcohol concentration. For these solutions, the CD and absorption spectra are practically constant and characteristic of unaggregated Amphotericin

ISSN:0006-3525    

DOI:10.1002/bip.1977.360161107

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

年代:1977

数据来源: WILEY

摘要:

AbstractThe binding of Mn2+to yeast tRNAPheat 25°C is measured by esr, and found to depend strongly on the concentration of monovalent cations, showing the importance of electrostatic effects. In low sodium (50mM/l.), the affinity and the curvature are reduced. In a limited range of sodium concentrations (15–30mM/l.), the folding of tRNA which is induced by the divalent ions results in cooperative binding, leading to upwards convexity of the Scatchard plot. An electrostatic model is developed, based on a single type of binding site which we take to be the phosphates, with a binding constant for Mn2+in the range of that found for ApA, 10 l./M. We compute the change in the binding constant due to the electrostatic potential of the distant charges (other phosphates and counterions), using a single set of parameters for all sodium concentrations. The model predicts that the plots in low sodium are curved, and a good fit to the experimental results is obtained: it is therefore not legitimate or necessary to interpret these results in terms of two types of binding sites. In high salt, the model gives plots that are only slightly curved, corresponding to weaker electrostatic effects. This shows that a search for sites with a special binding mode should be done in high salt. The computed plots are in good agreement with the data, except for slight differences concerning the first bound ions, which give a possible indication in favor of special binding. Given the observation of one special site for Mg2+at 4°C in high sodium [Stein, A.&Crothers, D. M. (1976)Biochemistry15, 157–160] inE. colitRNAfMet, we have measured the binding of Mn2+at lower temperature. At 12°C, in both yeast tRNAPheandE. colitRNAfMet, the plots clearly indicate special binding. A site found in high sodium is on a very different footing from the four to six so‐called strong sites unduly derived from low‐salt bin

ISSN:0006-3525    

DOI:10.1002/bip.1977.360161108

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

年代:1977

数据来源: WILEY

摘要:

AbstractWater‐soluble, random copolymers containingL‐methionine andN5‐(3‐hydroxypropyl)‐L‐glutamine have been prepared, fractionated, and characterized. The thermally induced helix‐coil transitions of these copolymers in water have been investigated, and it has been found that incorporation of L‐methionine increases the helix content of the polymers at all temperatures in the range of 0–60°C. The Zimm‐Bragg parameters σ andsfor the helix‐coil transition in poly(L‐methionine) in water were deduced from an analysis of the melting curves of the copolymers using the methods de

ISSN:0006-3525    

DOI:10.1002/bip.1977.360161109

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

年代:1977

数据来源: WILEY

摘要:

AbstractThe amino‐acid‐sequence distribution in poly(γ‐benzyl‐L‐glutamate,L‐methionine) prepared by polymerization of the respectiveN‐carboxyanhydrides has been investigated. This copolymer was converted first to poly(L‐glutamic acid,L‐methionine), which was subsequently cleaved by treatment with cyanogen bromide. The resulting material was fractionated into oligomers of (glutamic acid)n‐homoserine whose relative molar amounts were determined quantitatively. The results have been compared with those for a random incorporation of the methionine in a γ‐benzylglutamate host polymer. Fairly close a

ISSN:0006-3525    

DOI:10.1002/bip.1977.360161110

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

年代:1977

数据来源: WILEY

摘要:

AbstractWe develop a force‐constant refinement procedure which we believe capable of being used in problems of large molecules and biopolymers. The procedure is based on a Green‐function expression which relates changes in frequency to changes in force constants. The method does not require that assignments be made before refinment (although they may be). An expansion of this expression gives rise to a set of linear algebraic equations for the force‐constant corrections, rather than an equation involving residuals to minimize. The resulting calculations are considerably simpler. This approximate is iterated to find the final refined force‐constants. We discuss several methods of improving the convergence of the procedure which take into account the experimental information which may be available. Of particular interest is a scheme to select the force constants to be refined by imposing a criterion for selecting those which will fit the experimental data with the smallest changes of the force constants from their expected values. We discuss some limitations which occur for all methods of refinement applied to large mo

ISSN:0006-3525    

DOI:10.1002/bip.1977.360161111

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

年代:1977

数据来源: WILEY