ISSN:0006-3525    

DOI:10.1002/bip.360231002

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

年代:1984

数据来源: WILEY

摘要:

AbstractThe nature of the interhelix interaction in two‐chain, α‐helical, coiled coils is studied by experiments on the formation of hydrid molecules in which one helical chain is an α‐tropomyosin and the other a β‐tropomoysin. By means of a recently developed assay, the population of heterohelical (i.e., αβ hybrid) molecules relative to their homohelical (αα and ββ) parent species is determined under a variety of conditions, both equilibrium and nonequilibrium. It is found that mixed intact αα and ββ molecules do not form hybrid species in detectible amounts even after incubation at room temperature (or below) for periods of over one week. That the lack of αβ species in this “native‐exchange” system is a result of a kinetic barrier is evident from experiments involving a thermal denaturation–renaturation cycle in which the largely dissociated, unfolded chains at higher temperature are annealed to benign temperatures over a period of 6 h, thus assuring an equilibrium population of two‐chain species. In the resulting equilibrium state, the αβ population is one‐half the total, indicating that recombination is random. Furthermore, this same (equilibrium) state is reached if the separated, mostly unfolded chains are renatured by a rapid (∼ 40 s) quench to benign temperatures. Some implications of these results for the thermodynamics of interhelix interation, for kinetics of chain dissociation and recombination, and forin vivogenesis o

ISSN:0006-3525    

DOI:10.1002/bip.360231003

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

年代:1984

数据来源: WILEY

摘要:

AbstractThe distribution of twist and writhing in a closed DNA shorter than its persistence length is examined. In this case, the only energy contribution is elastic. We have in tegrated the equations of elasticity for a homogeneous axially symmetric rod of undeformable infinitely small circular cross section with frictionless reactions, when there is no or only one self‐contact. In the absence of self‐contacts, the central line of the rod is drawn on a toroid. It makes ν turns around the axis of revolution of the toroid andmturns around its core. The integer, ν, is equal to one if the rod is unknotted. We prove that no infinitely thin rod with a positive Poisson ratio is stable in a toroidal conformation if there is no self‐contact. However,m‐leafed roses or rosettes, with but one multiple self‐contact, are shown to actually be stable when their writhing is not too great. When the integer,m, is equal to two, we have figure‐8 conformations. Buckling of the circle into a figure‐8 conformation occurs for the constraint such that the figure‐8 and the circular conformations have the same energy. This constraint is 1.845 turns for a bending‐to‐twisting elastic constants ratio ofA/C= 1.5. For the same value ofA/C, the figure‐8 conformation is unstable for a constraint greater than 2.4 turns. Corrections caused by a finite value of the radius ratio,a/L, of the cross section to the length of the rod, are estimated. For instance, both the circular conformation and the infinitesimally warped circle are simultaneous solutions for particular values of the β twist. β =A/C(m2− ν2)½[1 + (νπa/L)2/2]. The binding of ethidium to DNAs short enough to follow first‐order elasticity has been studied. Buckling occurs at an apparent average constraint of about 0.6. How the DNA molecules are distributed in figure‐8 conformations and circles has been determined as t

ISSN:0006-3525    

DOI:10.1002/bip.360231004

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

年代:1984

数据来源: WILEY

摘要:

AbstractThe intrachain reaction theory of Wilemki and Fixman [(1974)J. Chem. Phys.60, 866–877] is used to assess the influence of internal DNA motions on various protein–DNA association schemes. It is found that, for large proteins, the diffusional association rate can be totally dominated by these motions rather than by the free‐trans‐lational diffusion rates. Also, the time required for the diffusion together of two DNA segments is estimated. This estimate can be used to provide an upper limit for the rate of intrachain cyclization, and also for the effective intrachain transfer rate of a protein bound to a DN

ISSN:0006-3525    

DOI:10.1002/bip.360231005

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

年代:1984

数据来源: WILEY

摘要:

AbstractAbsorption, CD, and LD spectra of the π‐π* transition near 200 nm are calculated for poly(Gly‐X‐Y) (X,Y = Gly, Ala, Pro) in four conformations proposed for collagen like triple helices in the recent literature. A dipole interaction model is used with the same optical paramenters as in previous studies of polypeptide spectra. The CD spectra are sensitive to backbone structure and amino acid composition, although the experimentally observed negative peak near 200 nm is a general feature of most the calculated spectra. Interchain interactions significantly affect the CD spectra in most cases. Calculations for (Gly‐Pro‐Ala)3and (Gly‐Ala‐Pro)3in the triple helical structure of Fraser, MacRae, and Suzuki [(1979)J. Mol. Biol.129, 463–481] show absorption, CD, and LD spectra in fairly good agreement with experiment. The characteristics of the π‐π* normal modes responsible for the calculated spectra are compared with those of the component bands resolved from the experimental spectra of collagen by Mandel and Holzwarth [(1973)Bi

ISSN:0006-3525    

DOI:10.1002/bip.360231006

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

年代:1984

数据来源: WILEY

摘要:

AbstractIn chloroform solution, theD,L‐alternating stereo‐co‐oligopeptide HCO‐L‐Phe‐(D‐Phe‐L‐Phe)3‐OMe (I) forms three major species, two of which are dimeric and one tetrameric. One of the two dimeric species gives a specific set of1H‐nmr signals at 25°C; the other, together with the tetrameric species, gives another set of resonance signals. In a carbon tetrachloride or cyclohexane solution at 25°C, I forms virtually only the tetrameric species. From the nmr data, it can be shown that the dimeric and tetrameric species, that are in rapid equilibrium with each other in chloroform solutions, are a right‐handed ↑↑β5.6helical dimer and the head‐to‐head (formyl‐ends‐to‐formyl‐ends) dimerization product of this dimer. It is suggested that the linear gramicidins may also form head‐to‐head dimers of parallel β he

ISSN:0006-3525    

DOI:10.1002/bip.360231007

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

年代:1984

数据来源: WILEY

摘要:

AbstractSolution‐phase Raman spectra of diastereomeric alanyl dipeptides,D‐Ala‐L‐Ala andL‐Ala‐L‐Ala, and various mono‐ and dideuterated isotopomers in H2O and D2O, are reported. Spectral differences between the diastereomeric forms are interpreted, using the Raman analog of the coupled oscillator model, in terms of geometric differences between certain vibrations in the diastereomeric forms. Application of the coupled‐oscillator formalism allows the determination of a dihedral angle between the coupling vibrations. The results are compared with vibrational coupling employed by other workers in the determination of the vibrational sp

ISSN:0006-3525    

DOI:10.1002/bip.360231008

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

年代:1984

数据来源: WILEY

摘要:

AbstractInfrared absorption and resonance Raman spectroscopy (RRS) are used to study poly(dG‐dC)·poly(dG‐dC) in two different forms: the right‐handed B form at low ionic strength and the left‐handed Z form at high ionic strength. The existence of a new electronic absorption band in the 290–300‐nm region is evidenced by uv RRS studies of the Z form at different wavelengths of excitation. Infrared absorption spectra prove that this new electronic band is polarized perpendicularly to the cytosine plane. The possibility of anπ* character of this transition moment

ISSN:0006-3525    

DOI:10.1002/bip.360231009

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

年代:1984

数据来源: WILEY

摘要:

AbstractThe thermodynamic quantities of solvation, that is, Gibbs free energy, enthalpy, and entropy for the transfer of lysozyme and β‐lactoglobulin A from water to 6Mguanidinium chloride solution, were calculated from the respective contributions of constituent groups. Comparison of the calculated values with the experimental ones reveals satisfactory agreement for lysozyme, whereas for β‐lactoglobulin A, it is semiquantitative. Thus the method of calculation appears to be fundamentally sound. The reasons for the differences in calculated and experimental value are briefly disc

ISSN:0006-3525    

DOI:10.1002/bip.360231010

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

年代:1984

数据来源: WILEY

摘要:

AbstractThe conformational equilibria of five β‐cellobiose conformers have been studied theoretically in 10 solvents. The stability of the conformers in dilute solution has been compared by using the method that has already been tested for 2‐methoxytetrahydropyran, β‐maltose, andD‐glucose. The solvation energy consists of electrostatic, dispersion, and cavity terms which have been determined from the properties of the solute calculated by the PCILO quantum‐chemical method and physicochemical properties of the solvents. The calculated abundance of conformers depends on the solvent (e.g., in dioxaneC1:C2:C3:C4:C5 = 60.0:34.1:2.9:2.0:1.0; in dimethylsulfoxide, 75.5:22.1:1.8:0.5:0.2; and in water, 82.2:16.2:1.3:0.2:0.1). The results obtained indicate that the preponderant conformer in the aqueous solution is similar to the one adopted by β‐cellobiose in the crystalline form. The role of individual contributions to the solvation energy have been analyzed. Based on the determined abundance of conformers, averaged residual optical activity and nmr parameters have been calculated and compared with observable properties. The marked differences observed between solvent‐induced conformational changes for β‐cellobiose and β‐maltose have been discussed from the viewpoint of the solub

ISSN:0006-3525    

DOI:10.1002/bip.360231011

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

年代:1984

数据来源: WILEY