ISSN:0006-3525    

DOI:10.1002/bip.1974.360130502

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

年代:1974

数据来源: WILEY

摘要:

AbstractThe conformation of deoxyribonucleoprotein (DNP) from calf thymus at different stages of deproteinization was studied.The dissociation of the first portion of histone produces no effect on the hydrodynamical and optical behavior of DNP particles. The conformational transition of a macromolecule was observed as soon as the ratio of protein to DNA ⩽ 0.9.The effect of ionic strength on the conformation of DNP particles with high protein content was more strongly pronounced than that for DNA. On the contrary, DNP particles depleted of proteins (protein/DNA<0.9) were found to be less sensitive than DNA to the variation of ionic strength. These data imply that the DNP molecules rich in proteins possess a superstructure that is destroyed as the protein/DNA ratio becomes 0.9.The data were analyzed in view of current theories on various model concepts. The most probable model to describe the DNP molecule was chosen by comparing the calculated and experimentally obtained parameters. We believe that DNP is best described as a “compressed coil,” possibly including superhelical re

ISSN:0006-3525    

DOI:10.1002/bip.1974.360130503

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

年代:1974

数据来源: WILEY

摘要:

AbstractSamples of epichlorohydrin crosslinked potato starch were prepared by using a high ratio of starch to water and alkali concentration below the gelatinization level. This yielded crosslinked samples that were partially crystalline, and where the number of crosslinks could be varied between 1 and 20 crosslinks per 100 anhydroglucose units. The degree of swelling varied regularly with degree of crosslinking, and the molecular weight between crosslinksMcas derived from swelling data in a good swelling agent compared favorably withMcderived from chemical analysis.From the heat of gelatinization of the crosslinked starches, as observed in a differential scanning calorimeter, for gelatinization in glycerol, water, and dimethylsulfoxide, a model for the gel state of the crosslinked starch is proposed. It is concluded that the entropy of melting is the determining factor in establishing the temperature of gelatinization.

ISSN:0006-3525    

DOI:10.1002/bip.1974.360130504

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

年代:1974

数据来源: WILEY

摘要:

AbstractA mixture of acids with known pK′ and in a known concentration was dissolved to simulate the ionic character of hemoglobin. The titration curves of the mixture were obtained in water and 3.6MKCl at 20°C. These curves were subjected to analysis by a reiterative curve‐fitting procedure to determine if one could evaluate both the group ionization constants and the numbers of groups. This approach was successful in that the calculated parameters were within the experimental error encountered in obtaining these constants on each of the model compounds. However, analysis for the electrostatic interaction parameterwindicated that there was a possible effect on the ionization of formic acid, pyridine, imidazole, and the α‐amino group of glycylglycine in water and on imidazole and the α‐amino group of glycylglycine

ISSN:0006-3525    

DOI:10.1002/bip.1974.360130505

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

年代:1974

数据来源: WILEY

摘要:

AbstractClipped autocorrelation functions for the fluctuating intensity of light scattered from dilute solutions of poly‐L‐lysine in 0.2MNaBr have been observed over a wide range of time scales down to 1.83 μsec, and over a wide range of pH. Two poly‐L‐lysine samples of molecular weight 35,000 and 200,000, respectively, were compared to determine the extent of draining of the so‐called random‐coil configuration. The observed correlation functions were in general very satisfactorily represented by simple translation diffusion of single molecules. At high pH ∼10–10.4, there was evidence of considerable aggregation, but no indication whatsoever of any unusually fast component, as reported recently by Jamieson et al. for poly‐L‐lysine HBr in the absence of salt.A 30% rise in the diffusion coefficient to a peak at pH 10 parallels the previously reported dip in the intrinsic viscosity, and is interpreted in terms of a more compact structure in that pH region between the coi

ISSN:0006-3525    

DOI:10.1002/bip.1974.360130506

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

年代:1974

数据来源: WILEY

摘要:

AbstractCircular dichroism studies of the interaction of β‐cyclodextrin with a series of eight dinucleoside phosphates, and with 3′‐AMP are reported. From results with ApU and ApA, it is shown that β‐cyclodextrin binding is sensitive to dinucleoside stacking in approximately the same way as optical measures of stacking. Some qualitative uses of β‐cyclodextrin binding are suggested, based on the fact that the change in the CD spectrum caused by cyclodextrin binding is unique to each of the dinucleosides studied. Hoffman and Bock have previously suggested the use of β‐cyclodextrin as a probe of nucleic acid structure. Their work indicated that only binding to adenosine and inosine would have to be considered. The present paper shows that binding to other bases cannot be neglected, and will impose serious restrictions on the use of β‐cyclodextrin as

ISSN:0006-3525    

DOI:10.1002/bip.1974.360130507

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

年代:1974

数据来源: WILEY

摘要:

AbstractA theoretical analysis is given of the triple‐helix–random‐coil transition in a mixed solution of poly(Pro‐Pro‐Gly)nwith two different but defined degrees of polymerizationnandn′. Because of the highly cooperative nature of this helix–coil transition, each polypeptide chain tends to form a triple helix with other polypeptide chains with the same degree of polymerization (size recognition). Occurrence of triple helices consisting of polypeptide chains with different degrees of polymerization (error in recognition) is studied in detail as a function of the cooperativity, andnandn′. Implication of this analysis for molecular recognition in gener

ISSN:0006-3525    

DOI:10.1002/bip.1974.360130508

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

年代:1974

数据来源: WILEY

摘要:

AbstractThe location of transverse bands within the major repeating period of positively stained collagen fibrils was determined from electron micrographs by an optical averaging procedure. From these data and the published location of bands in SLS crystallites, we have prepared a two‐dimensional representation, accurate to about 25 Å, of the modified quarter‐stagger arrangement of molecules in the collagen fibril. With this information it is possible to demonstrate the relationship of loci on individual collagen molecules within the fibril. For example, the site where the collagen molecule is cleaved by tadpole collagenase, the site where a disaccharide unit is covalently bound to the α1‐CB5 peptide, and the site of carboxyl‐terminal intermolecular cross‐linking all occur in the fibril near the amino‐terminal edge of the “hole zone;” and the site of amino‐terminal cross‐linking occurs near the carboxyl‐terminal

ISSN:0006-3525    

DOI:10.1002/bip.1974.360130509

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

年代:1974

数据来源: WILEY

摘要:

AbstractThe synthesis of some high‐molecular‐weight protenoid structures in radiofrequency cold plasma conditions are discussed. The fractionation results of the raw product and the spectrum of free and protenoid‐bound amino acids are given. The uv analysis of these compounds is presented.A protein‐forming mechanism that might have existed on the primitive earth is p

ISSN:0006-3525    

DOI:10.1002/bip.1974.360130510

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

年代:1974

数据来源: WILEY

摘要:

AbstractCovalently closed intracellular DNA obtained fromPseudomonasBAL 31 20 min after infection with PM2 phage has been shown to be heterogeneous in superhelix density. Analytical band sedimentation, in the presence of low concentrations of ethidium bromide, has been carried out on fractions centripetal and centrifugal to the mode of a single band of closed circular DNA in a preparative propidium iodide–CsCl buoyant density gradient. Different average sedimentation rates, as well as different band shapes, have been observed for upper and lower fractions centrifuged at a dye concentration near the minimum ins°versusethidium bromide concentration titrations performed on DNA from proximate intermediate fractions. Similar differences, although not as pronounced, have been obtained at a dye concentration corresponding to a point in the steep region of the titrations. Differential band sedimentation experiments performed on the same fractions have confirmed these results.Differential band sedimentation experiments on similarly fractionated mature PM2 I DNA (closed circular form) have shown slight differences in the relative sedimentation rates of upper and lower fractions at dye concentrations corresponding to the steep regions in the titrations. The same experiments, when performed on nicked circular DNA obtained from heating both the mature and intracellular fractions, showed no evidence of differences in sedimentation coefficients. Such results may indicate slight heterogeneity in the superhelix density of viral PM2 I DNA; however, the degree of this heterogeneity would be somewhat less than that of the intracellular DNA.The possibility that superhelix density heterogeneity may arise from displacement loops, which have been found at low levels in intracellular PM2 DNA, has been subjected to experimental tests. Unless such structures are originally present and removed by the isolation procedure, this possibility may be reject

ISSN:0006-3525    

DOI:10.1002/bip.1974.360130511

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

年代:1974

数据来源: WILEY