摘要:

AbstractThe strength of fibrin gels has been investigated by a recently developed laser light scattering technique for determining the shear modulus of soft gels. By this method, changes in the modulus were monitored as a function of time without perturbing the material. Fibrin gels were crosslinked with blood coagulation factor XIII. Rigidity measurements and SDS–polyacrylamide gel electrophoresis were used to correlate gel strength with the number of covalently bonded subunit chains. The modulus was found to vary linearly with the number of crosslinks until maximum rigidity was achieve

ISSN:0006-3525    

DOI:10.1002/bip.1980.360190702

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

年代:1980

数据来源: WILEY

摘要:

AbstractConformations of terminal peptide units of α‐helical poly(γ‐benzyl‐L‐glutamate), poly‐[Glu(OBzl)], were examined by an induced circular dichroism (CD) of chromophores which were covalently attached to both ends of the chain. In chloroform, where the helical poly‐[Glu(OBzl)]exists as a head‐to‐tail‐type dimeric associate, the chromophores showed a strong CD induced by an asymmetric perturbation from the helical structure. The induced CD almost disappeared by an addition of a few percent of dichloroacetic acid, which has been reported as a powerful breaker of the associate. These results are explained by an incorporation of terminal peptide units into a helical conformation in the head‐to‐tail associate and a local unfolding of the terminal portions by the addition of acid. An induced CD of a charge‐transfer complex between the two terminal chromophores was also observed and the structure of the helix–helix junction of the head

ISSN:0006-3525    

DOI:10.1002/bip.1980.360190703

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

年代:1980

数据来源: WILEY

摘要:

AbstractThe binding constant of methyl‐2‐aminobenzoate to beta‐cyclodextrin was determined by fluorescence titration to be 92.1M−1at 25°C in pH 7 buffer. Beta‐cyclodextrin dramatically protects methyl‐2‐aminobenzoate against quenching by iodate and protects, though much less efficiently, against the smaller quencher, iodide. The observed decrease in fluorescence lifetime of the methyl‐2‐aminobenzoate‐beta‐cyclodextrin complex on addition of quencher indicates that the quenching mechanism is collisional (dynamic). The dependence of quenching rate on solvent viscosity is less than expected from simple theoretical considerations. However, the extent of beta‐cyclodextrin protection is essentially viscosity‐independent. These model studies show the usefulness of iodate as a quencher and encourage further attempts at quantitative interpretation of quenching studies on chromophor

ISSN:0006-3525    

DOI:10.1002/bip.1980.360190704

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

年代:1980

数据来源: WILEY

摘要:

AbstractIn a recent paper, we developed a thermodynamic theory on the complex coacervation in the absence of low molecular ions, under the assumption that the coacervation is a condensation phenomenon of aggregates of polyanion and polycation in the aqueous solution, by obtaining the interaction potentialUSbetween these aggregates on the basis of Flory's method. In this paper, we have extended the theory to a more complicated phenomenon of the counterion‐containing solutions. This treatment has led the interaction potential having an additional contribution toUSresulting from an entropy increase by the counterion distribution. The phase diagram between solution (sol) and separated phase has been obtained as a function of the difference of charges between polyanion and polycation. It has been found that the presence of counterions sensitively suppresses the coacervatio

ISSN:0006-3525    

DOI:10.1002/bip.1980.360190705

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

年代:1980

数据来源: WILEY

摘要:

AbstractThe fixation ofcis(NH3)2Cl2Pt(II) to poly(I)·poly(C) leads to the formation of two complexed species. One involves coordination to a single base (accounting for about 70% of the total platinum bound over therbrange 0.07–0.25) and the other to two bases which are not adjacent to each other but may be on the same strand and separated by a loop. Reaction of the platinum compound with poly(I) gives in addition to the above two species a minor one (about 15%, independent ofrbover the range 0.05–0.30) in which the platinum is bound to two adjacent bases. The availability of such coordination reduces the dominance of the 1:1 species, which, however, remains the major one (ca.

ISSN:0006-3525    

DOI:10.1002/bip.1980.360190706

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

年代:1980

数据来源: WILEY

摘要:

AbstractHelix–coil transition in very long DNA (containing hundreds of thousands of nucleotides or more) is considered. Certain statistical information about DNA nucleotide sequence is obtaine

ISSN:0006-3525    

DOI:10.1002/bip.1980.360190707

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

年代:1980

数据来源: WILEY

摘要:

AbstractThe thermal stability and renaturation kinetics of DNA have been studied as a function of dimethyl sulfoxide (DMSO) concentration. Increasing the concentration of DMSO lowers the melting temperature of DNA but results in an increased second‐order renaturation rate. For example, in a DNA solution containing 0.20MNaCl, 0.01MTris (pH 8.0), and 0.001MEDTA, the addition of 40% DMSO lowers the melting temperature of the DNA by 27°C and approximately doubles the optimal renaturation rate. The effect of DMSO on the renaturation rate is shown to be at least partially due to its effect on the solution dielectric constant and to be consistent with the polyelectrolyte counterion condensation theory of Manning [(1976)Biopolymers15, 1333–1

ISSN:0006-3525    

DOI:10.1002/bip.1980.360190708

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

年代:1980

数据来源: WILEY

摘要:

AbstractThe complex of CH3Hg(II) with the accessible cysteines of glyceraldehyde‐3‐phosphate dehydrogenase (GAPD, EC 1.2.1.12) from rabbit muscle has been studied by phosphorescence and optically detected magnetic resonance (ODMR) spectroscopy. The wavelength dependence of the phosphorescence decay kinetics has also been measured. Comparison of CH3Hg(II)–GAPD with GAPD by these methods shows that a specific optically resolved tryptophan site of GAPD is perturbed by the interaction with a nearby mercury atom. The perturbation on the luminescence and ODMR properties is typical of an external heavy‐atom effect. Based on the x‐ray diffraction structure of the lobster enzyme, it is proposed that the heavy‐atom effect results from the interaction of tryptophan‐310 with CH3Hg(II) bound to cysteine‐281 in the rabbi

ISSN:0006-3525    

DOI:10.1002/bip.1980.360190709

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

年代:1980

数据来源: WILEY

摘要:

AbstractSemiempirical quantum chemical calculations were carried out using the CNDO/2 and the INDO methods on the model compoundcis‐N‐methylacetamide in order to get an insight into the problem of possible nonplanar distortions of thecis‐peptide unit. In addition, the crystal structure data of cyclic peptides containingcis‐peptide units were analyzed. These studies have indicated that the dihedral angles θNand Δωare correlated approximately by the relation Δω= −θN, whereas θCis small and is uncorrelated with Δω, as was found in the case of thetrans‐peptide unit. Both theory and crystal data suggest that out‐of‐plane distortions at the nitrogen atom of the peptide unit were quite likely to occur and should be included in the conformational calculations. The average geometry for the planarcis‐peptide unit has also been obtained

ISSN:0006-3525    

DOI:10.1002/bip.1980.360190710

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

年代:1980

数据来源: WILEY

摘要:

AbstractLight‐scattering, viscosity, and sedimentation experiments on aqueous solutions ofk‐carrageenan show that this sulfated polygalactose is an expanded flexible random coil. This expansion is due to long‐range interactions that are predominantly electrostatic. Extrapolation of viscosity data to infinite ionic strength provided values for the intrinsic viscosity which were subjected to the Stockmayer‐Fixman analysis, giving a value for the Mark‐Houwink coefficient under theta‐conditions,Kθ, of 0.27. The characteristic ratio,C∞, under these conditions is 7.8, and the conformation factor σ is 2. In a solution of 0.118 ionic strength, where a Mark‐Houwink exponentaηof 0.86 is found, the radii of gyration calculated from viscosity data are lower than those found from the angular dependence of scattered light. On the other hand, the radius of gyration found from the sedimentation rate agrees well with the light‐scattering radius. The relations between molecular parameters are corrected for the poly‐di

ISSN:0006-3525    

DOI:10.1002/bip.1980.360190711

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

年代:1980

数据来源: WILEY