摘要:

AbstractThe early steps of fibrin aggregation induced by low Reptilase concentrations were studied by means of static and dynamic light scattering. In order to obtain information on the size and shape of the first oligomers, the angular dependence of the scattered intensity and the mean Rayleigh line width were measured. Under physiological pH and ionic strength, oligomer formation was detectable immediately after enzymatic activation. Comparison of the calculated data for different models with experimental results shows that the early fibrin polymerization proceeds as an end‐to‐end aggregation of elongated and possibly flexible molecules approximately 75 nm l

ISSN:0006-3525    

DOI:10.1002/bip.1981.360201002

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

年代:1981

数据来源: WILEY

摘要:

AbstractThe conformational characteristics of the amylose–iodine–iodide complex in aqueous solution, particularly for a rapidly mixed system, were studied by resonance polarized scattering measurements using a He‐Ne laser at low concentrations of the complex and by viscosity measurements at high concentrations of the complex. For the scattering measurements, the following results were obtained: the depolarization ratios ρuand ρvshowed a pronounced increase with the degree of saturation of the bound iodine (q) in amylose, depending on KI concentration. Atq≃ 0.7, the increase in these values appeared to be suppressed. However, the ρhvalue was approximately 1, irrespective ofq. Additionally, the dissymmetryZdecreased appreciably with increasingq. The conformational change of the complex withqwas characterized by the changes in the contour and persistence lengths of the chain and in the optical anisotropy of the scattering segments, which were obtained from numerical computations based on the polarized scattering equation for a wormlike‐chain model with a restriction by the entropy force of the chain. The viscosity of the complex solution decreased with increasingq; aboveq≃ 0.7 it increased strikingly. The conformational change of the complex withqwas characterized by the change in exponent α in the Houwink‐Mark‐Sakurada equation [η] =KMα. It was concluded that the iodine‐saturated complex has the characteristics of a rod, regardless of th

ISSN:0006-3525    

DOI:10.1002/bip.1981.360201003

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

年代:1981

数据来源: WILEY

摘要:

AbstractTwo series of peptides containingL‐phenylalanine, Nps‐(L‐Phe‐L‐Phe‐Gly)n‐OEt (n= 1–6) and Nps‐(L‐Phe‐L‐Leu‐Gly)n‐OEt (n= 1–7), were prepared by the fragment‐condensation method using the tripeptideN‐hydroxysuccinimide esters. Conformational characterization of these peptides in the solid state was performed by ir spectroscopy and x‐ray powder diffraction measurement. The peptides Nps‐(L‐Phe‐L‐Phe‐Gly)n‐OEt take the β‐structure, but the pentadecapeptide and higher peptides of Nps‐(L‐Phe‐L‐Leu‐Gly)n‐OEt form

ISSN:0006-3525    

DOI:10.1002/bip.1981.360201004

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

年代:1981

数据来源: WILEY

摘要:

AbstractThe equivalent conductivity of salt‐free solutions of deoxyribonucleates of alkali metals and ammonium obtained by filtering an isoionic DNA solution through a cation exchanger in the corresponding form has been investigated in the concentrations range of 1 × 10−4to 4 × 10−3M. For all counterions investigated there is a linear dependence of the equivalent conductivity on\documentclass{article}\pagestyle{empty}\begin{document}$ \sqrt {C_p} $\end{document}, whereCpis the nucleic phosphorus concentration. The limiting equivalent conductivity of deoxyribonucleates increases linearly with the limiting mobility of a counterion. By extrapolation to the zero mobility of the counterion, we have obtained the limiting mobility of a macroion, which is equal to 19 × 10−4Sm m2equiv.−1, which is in good agreement with the literature data for denatured DNA obtained by the method of a moving boundary. It is shown that the degree of binding of counterions calculated from the conductometric data in diluted DTA solutions in independent of the nature of the univalent counterion. The degree of dissociation of H+‐DNA in the isoionic solution calculated with allowance for the fraction of unprotonated bases practically coincides with this value for salts of DNA. The parameter of Manning's theory calculated from the experimental data corresponds to the distance between phosphates along the chain of the macroion, which is equal to 6.7 Å. We attribute the smaller value of this distance as compared with the theoretical one for denatured DNA to the aggregati

ISSN:0006-3525    

DOI:10.1002/bip.1981.360201005

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

年代:1981

数据来源: WILEY

摘要:

AbstractThe effect of excluded volume on the thermodynamic activity of globular macromolecules and macromolecular complexes in solution is studied in the hard‐particle approximation. Activity coefficients are calculated as a function of the fraction of total volume occupied by macromolecules using relations obtained from scaled particle and lattice models. Significant and readily observable effects are predicted to occur as the fraction of volume occupied by globular macromolecules increases, including the following: (i) Compact quasi‐spherical macromolecular conformations become increasingly energetically favored over extended anisometric conformations. (ii) Self‐ and heteroassociation processes are enhanced, particularly those leading to the formation of compact quasi‐spherical aggregates. (iii) Depending upon the details of the reaction mechanism, the rate of an enzyme‐catalyzed reaction may monotonically decrease, go through a maximum, or exhibit more complex behavior. A given degree of volume occupancy by larger macromolecules is predicted to have less effect on the structure and self‐association of smaller macromolecules than the same degree of volume occupancy by smaller macromolecules has on the structure and self‐association of larger m

ISSN:0006-3525    

DOI:10.1002/bip.1981.360201006

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

年代:1981

数据来源: WILEY

摘要:

AbstractThis report presents a quantitative test of the ability of the counterion condensation theory to describe the proton‐induced lowering of DNA melting temperature. From a general approach of Record et al. [Record, M. T., Anderson, C. F.&Lohman, T. H. (1978)Q. Rev. Biophys.11, 103–178], we have obtained an expression that may be computer‐fitted to the experimental data by numerical minimization of χ2. To do this, in addition to the assumptions made by Record et al., it was necessary to suppose that the interchange between protons and sodium is independent of pH and, due to the absence of data, take the enthalpies of protonation as thermally independent over the experimental temperature range. The dependences of the enthalpy of denaturation at neutral pH on sodium concentration and on G + C content were taken from literature. In the fitting process we have used 250 melting temperatures obtained at different pH and sodium concentrations for various natural DNAs. The theoretical expression gives a good quantitative description of the G + C and sodium concentration influences on the phenomenon but is only qualitative with respect to the dependence ofdT/dlog[Na+] on the pH. The adjusted pKvalues for the bases in denatured DNA agree with those for isolated deoxynucleosides. Interchange between sodium and protons is found to be less than 1:1. Calculated protonation enthalpies are ill‐defined because of their low numerical influence. In short, it appears that the theory gives a good description of most of the aspects of the phenomenon even if it has some shortcomings, perhaps due to the great number of ass

ISSN:0006-3525    

DOI:10.1002/bip.1981.360201007

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

年代:1981

数据来源: WILEY

摘要:

AbstractWe studied the kinetics of replacement of O2by CO in hemoglobin in the presence and absence of organic cosolvents (methanol, ethanol,iso‐propanol,n‐propanol, formamide, acetamide,N‐methyl‐formamide) and at 10 and 25°C. Quantitative analysis of the results indicates that these cosolvents do not affect the intrinsic binding constants of ligands to the heme when hemoglobin is in the R conformation. The present results confirm the previously reported suggestion that the effects of the above cosolvents on the oxygen affinity of hemoglobin are related to effects on the T ⇄ R conformational e

ISSN:0006-3525    

DOI:10.1002/bip.1981.360201008

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

年代:1981

数据来源: WILEY

摘要:

AbstractMeasurements have been made on the flow dichroism of T7 DNA as a function of NaCl concentration. In high salt, our results are compatible with an optical factor of −1.4 and a persistence length of 470 Å. The former is in agreement with expectations from the x‐ray diffraction structure of fibrous B–DNA, and the latter is in the midrange of recent determinations. As salt concentration is decreased, the persistence length increases. The relation of our study to other recent investigations and with current theories of the electrostatic contribution to persistence length is discussed. We note that the separation of the electrostatic expansion factor into long‐ and short‐range effects is somewhat arbitrary and might affect the interpretation of different experimental results in different ways. Finally, our hydrodynamic factors are consistent with a chain which is partially free‐draining. This goes against the traditional interpretation but is in agreement with two recent

ISSN:0006-3525    

DOI:10.1002/bip.1981.360201009

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

年代:1981

数据来源: WILEY

摘要:

AbstractA hydrate of cellulose II can be formed by swelling Fortisan fibers in hydrazine and then washing in water. The hydrate is stable at 93% relative humidity and has a monoclinic unit cell with dimensionsa= 9.02 Å,b= 9.63 Å,c= 10.34 Å, and γ = 116.0°; the space group isP21. The unit cell contains disaccharide sections of two chains and approximately four water molecules. The structure was refined using the LALS method, based on 10 observed and 10 unobserved reflections. An antiparallel arrangement of adjacent chains was assumed, since this occurs in cellulose II (the starting material), and the hydrate also reverts to cellulose II on dehydration. Refinement of the positions and side‐chain conformations of the chains shows that the chains are stacked in the same way as in cellulose II, and the hydrate is formed by insertion of water molecules between the stacks. However, all efforts to arrange the water molecules in crystallographically regular positions led to unsatisfactory agreement between the observed and calculated intensities. These results suggest an irregular arrangement of the water molecules, which was modeled using water‐weighted atomic scattering factors. The analysis resulted in two refined models with relative chain staggers of ∼ +c/4 and ∼ ‐c/4, which are indistinguishable in terms of the x‐ray agreement. Our preference is for the +c/4 model, for which the stacks of chains are analogous to those

ISSN:0006-3525    

DOI:10.1002/bip.1981.360201010

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

年代:1981

数据来源: WILEY

摘要:

AbstractAt sufficiently high ionic strength, long‐range electrostatic interactions in a polyelectrolyte such as poly(L‐glutamic acid) might be adequately approximated in matrix calculations by use of statistical weights representing second‐order interactions. The validity of this assumption has been investigated making use of experimental observations (CD spectra and titration curves) for poly(L‐glutamic acid) as a function of temperature in 0.1–0.5Msodium chloride. Theoretical analysis, using a statistical weight matrix proposed by Warashina and Ikegami, is based on the Zimm‐Rice theory. Implementation differs from that of Warashina and Ikegami in one respect. Refinement of the initial estimates is achieved using a form of the configuration partition function which does not assume diagonalization of the statistical weight matrix. This difference is of no consequence for the values of σ ands, but it does produce somewhat different values for the statistical weights used to represent the electrostatic interactions. The method used to treat electrostatic interactions in poly(L‐glutamic acid) in 0.1Msodium chloride can be viewed as successful in that it properly reproduces the helix–coil transition and titration curves in this solvent and the molecular‐weight dependence of the titration curves yields values forsin harmony with those obtained using a treatment which is independent of model, and gives a reasonable ionic‐strength dependence for the electrostatic parameters. Furthermore, the model can account for measured helix–coil transitions and titration curves in homopolypeptides in which the side chain is —(CH2)xNHCO(CH2)yCOOH. The model, however, is not exact. It does not properly account for the molecular‐weight dependence of the helical content for polymers of lo

ISSN:0006-3525    

DOI:10.1002/bip.1981.360201011

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

年代:1981

数据来源: WILEY