摘要:

AbstractThe influence of alcohol–water solvents on the conformation of native DNA was studied by the methods of flow birefrigence and viscometry. Conformational transitions of DNA were observed at low alcohol concentrations corresponding to the destruction of the water spatial structure. A change in the secondary structure of the DNA molecule was observed at high ethanol concentrations and is discussed in the pape

ISSN:0006-3525    

DOI:10.1002/bip.1974.360131102

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

年代:1974

数据来源: WILEY

摘要:

AbstractA conformational analysis was carried out in solution on a series ofL‐methionine oligomers having the general formula\documentclass{article}\pagestyle{empty}\begin{document}$ {\rm BOC\rlap{--} (L - Met\rlap{--})}_n {\rm OMe (}n = 2 - 7)$\end{document}. We examined these oligopeptides in TFE, HFIP, EG, and mixed organic–water media. The critical size for helix formation was found to be seven residues in TFE, whereas the β‐associated structure appears at the pentamer in EG and TFE–water (20 : 80, v/v). In HFIP, however, the oligomers exist essentially in an unordered conf

ISSN:0006-3525    

DOI:10.1002/bip.1974.360131103

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

年代:1974

数据来源: WILEY

摘要:

AbstractIn order to analyze the optical activity of poly‐N‐γ‐carbobenzoxy‐L‐α,γ‐diaminobutyric acid, the microscopic model we have previously worked out is here further developed. Comparison with experimental data allows us to formulate a hypothesis on the stereochemical interaction between the side chains and the backbone of the macromolecule, and on the dependence of the optical activity on the conformational state of the backbone itself. Finally, the thermodynamic parameters concerning the side chains

ISSN:0006-3525    

DOI:10.1002/bip.1974.360131104

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

年代:1974

数据来源: WILEY

摘要:

AbstractThe helix–coil transition of poly‐N5‐(3‐hydroxypropyl)‐L‐glutamine (PHPLG) has been studied in methanol–water by CD and cmr spectroscopy. For polydisperse PHPLG, two separate peaks arising from residues in helical and random‐coil conformations are observed during the transition for both main‐chain carbons. These results are discussed and compared to those observed in the case of a polymer sample obtained by racemization of PHPLG in 0.1MNaOH and of PHPLG samples of controlled molecular weight and dispersity. The dominant influence of the molecular‐weight heterogeneity on the double‐peak phenomenon has been verified. The linewidths and chemical shift of the13C resonances are discussed in terms of side‐chain–main‐chain interactio

ISSN:0006-3525    

DOI:10.1002/bip.1974.360131105

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

年代:1974

数据来源: WILEY

摘要:

AbstractOptical density, viscosity, and light scattering measurements for calf thymus DNA in water–N,Ndimethyl formamide (DMF) solutions are presented. DMF content varied between 0 and 60% (v/v) and DNA molecular weight varied between 15 × 106and 0.5 × 106. Complementary measurements of the solubility of adenine, thymine, guanine, and cytosine in H2O–DMF mixtures are presented. The denaturation temperature of DNA, manifested by about a 35% increase of optical density, is gradually depressed by increasing DMF content. However, a significant increase of OD occurs even before (and even after) the denaturation point, when DMF content is increased isothermally. The intrinsic viscosity also exhibits a large decrease when DMF content is increased both before and after the denaturation point. Light scattering data for high‐molecular‐weight DNA in the predenaturation range indicate a decrease of the mean‐square radius and a constant molecular weight on increasing DMF content. The results, interpreted in terms of the wormlike chain of Kratky and Porod, indicate a large decrease of the persistence length of DNA. For low‐molecular‐weight DNA, radius and molecular weight increase with DMF content, indicating intermolecular aggregation. The formation of compact structures of native DNA is discussed in terms of an increased solubility of uncharged bases, and a decreased solubility of phosphate and deoxyribose groups, when a less polar environment is provided by the

ISSN:0006-3525    

DOI:10.1002/bip.1974.360131106

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

年代:1974

数据来源: WILEY

摘要:

AbstractOligonucleotide mixtures produced by the digestion of RNA by specific nucleases can be defined in terms of isostichs (sets of common chain length), compositional isomers, and sequence isomers. Equations are derived to express the distribution of radioactivity on the isostich length, the distribution of compositional isomers on the isostich length, and the distribution of compositional isomers on the proportion of total radioactivity (“intensity”). It is shown how the properties of a “fingerprint” may be calculated from first principles, and conversely how the complexity of a sequence may be estimated from its fingerprint.The equations are tested by means of computer simulations of RNA digestions and their range of applicability is determined.The three distributions are used to analyze the digests of repetitious sequences. It is shown how the parameters of a diverged sequence family can, in a favorable case, be deduced from its fing

ISSN:0006-3525    

DOI:10.1002/bip.1974.360131107

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

年代:1974

数据来源: WILEY

摘要:

AbstractThe buoyant densities of natural and synthetic DNA's can be accurately interrelated if second‐neighbor influences are taken into account. We derive the following expressions, based partly on the buoyant densities of six synthetic DNA's, for the buoyant densities ρ (g/cm3) of DNA's having random sequences. In CsCl,\documentclass{article}\pagestyle{empty}\begin{document}$$ \rho = 1.659 + 0.099H_{\rm G} - 0.065\,H_{\rm G} ^2 + 0.080\,H_{\rm G} ^3 $$\end{document}and in Cs2SO4,\documentclass{article}\pagestyle{empty}\begin{document}$$ \rho = 1.417 + 0.011\,H_{\rm G} - 0.004\,H_{\rm G} ^2 + 0.035\,H_{\rm G} ^3 $$\end{document}. In these equations,HGis the mole fraction of G : C base pairs in the DNA and the buoyant densities are calculated relative to densities forE. coliDNA of 1.703 and 1.426 (g/cm3) in CsCl and Cs2SO4, respective

ISSN:0006-3525    

DOI:10.1002/bip.1974.360131108

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

年代:1974

数据来源: WILEY

摘要:

AbstractProton and phosphorus‐31 nuclear spin‐lattice relaxation times (T1) have been measured with the Fourier‐transform method at 100 and 40.5 MHz, respectively, on single‐stranded polyriboadenylic acid (poly(A)) in a neutral D2O solution in the temperature range of 14–82°C.T1minimum is observed around 35–45°C for H(8), H(1′), and phosphorus resonances. Rotational correlation times have been deduced from theT1data, which indicate that the sugar–phosphate backbone as well as the base–sugar segment is undergoing rapid internal motion of 10−8–10−10sec range. The molecular motion of the sugar–phosphate backbone as deduced from the phosphorus relaxation is well‐characterized by a single activation enthalpy of 8.1 kal/mole for the whole temperature range of 14–82°C. Activation enthalpies of similar magnitude have been obtained for the motion of the adenine–ribose moiety from H(8) and H(1′) relaxation. The relative magnitude ofT1for H(8) and H(1′) infers that the poly(A) nucleotide exists on the average asantiin the single‐stranded form. The phosphorusT1value is consistent with a conformation such that both C(4′)–C(5′) and C(4′)–C(3

ISSN:0006-3525    

DOI:10.1002/bip.1974.360131109

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

年代:1974

数据来源: WILEY

摘要:

AbstractThe angular distribution of scattered intensity and decay times of concentration fluctuations have been measured by means of digital photon counting and single‐clipped photon correlation for solutions of Group C meningococcal polysaccharides at 31°C. Thez‐average diffusion coefficient 〈D〉zand its second moment 〈D2〉zhave been determined from the time‐dependent correlation function using the cumulant expansion technique. Very low observed values of 〈D〉zand the tremendous width of the polydispersity index, which is thez‐average normalized variance, suggest a higher degree of aggregation than the monomer–dimer type self‐association

ISSN:0006-3525    

DOI:10.1002/bip.1974.360131110

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

年代:1974

数据来源: WILEY

摘要:

AbstractThe hexamer of phycocyanin fromPhormidium luridumhas been isolated and purified by ammonium sulfate fractionation and gel chromatography. The protein is characterized by the sedimentation constantS°20, w= 10.2S, the diffusion coefficientD20, w= 4.73 × 10−7cm2/sec, and intrinsic viscosity [η] = 3.89 ml/g. The molecular weight of the aggregate is 209,000. The shape and dimensions of the hexamer are discussed in terms of a model consisting of subunits arranged with C6symmetry. The monomers, assumed to be spherical, are found to have a radius of 22 Å, and the diameter across the hexamer is 132 Å. The latter figure agrees closely with dimensions observed in electron micro

ISSN:0006-3525    

DOI:10.1002/bip.1974.360131111

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

年代:1974

数据来源: WILEY