摘要:

AbstractPolarized luminescence was used to study the mobility of tryptophan residues in polypeptide chains of different chemical composition and structural organization. It has been shown that the luminescence depolarization of tryptophan residues in coillike, helical, and β‐structural polypeptide chains is mainly caused by “fast” torsional vibrations and “slow” rotational isomerization of indole groups of tryptophan side chains. The characteristics of these types of motions are practically the same for tryptophan residues included in coillike chains of different chemical structure. Helix–coil transitions in copolymers of glutamic acid and lysine with tryptophan (Glu, Trp) and (Lys, Trp) (where side groups of tryptophan residues weakly interact with the surrounding side groups) do not appreciably change the amplitude of torsional vibrations or rotational isomerization. At the same time, in the helical state of glutamic acid–leucine–tryptophan copolymers (Glu, Leu, Trp) and in the β‐structural state of (Lys, Trp) copolymers (where direct interactions of Trp side groups with other side groups are possible), the amplitudes of the torsional vibrations are smaller and the rotational isomerization times larger than in the coil. The transition of (Glu, Leu, Trp) polypeptide chains into a compact state is accompanied by a marked decrease of both “fast” and “slow” intra‐molecular mobility and by an increase of the contribution made by the rotation of the macromolecule as a whole, as shown by the decrease of

ISSN:0006-3525    

DOI:10.1002/bip.1981.360201102

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

年代:1981

数据来源: WILEY

摘要:

AbstractAbsorption and CD spectra of the π‐π* transition near 200 nm are calculated for helical (Pro)nI and II (n= 6, 10) using the dipole interaction model, including interactions among all atoms, with optical parameters obtained from previous studies of related molecules. Calculated spectra for (Ala)nand (Pro)nin the same conformation show marked differences. The spectra for (Pro)nare sensitive to side‐chain structure but are found to agree reasonably well with exeriment for forms I and II when the side‐chain CC bond length is set at 1.54 Å, with structural data otherwise obtained from x‐ray diffrac

ISSN:0006-3525    

DOI:10.1002/bip.1981.360201103

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

年代:1981

数据来源: WILEY

摘要:

AbstractWe present a model to describe the equilibrium binding properties for the attachment of multivalent ligands to mobile receptors in membranes. The interaction is assumed to be governed by two inherently different association constants. The first of these controls the initial attachment of a ligand to its first receptor, by adsorption from bulk solution, while the second governs subsequent receptor attachments to this initially bound ligand by rearrangement of membrane‐bound species. Simple statistical mechanical expressions are used to estimate contributions to these association constants that are attributable to losses of translational and rotational degrees of freedom occurring upon binding. Suitable combinatorial expressions are combined with these association constants to derive the concentrations of bound species and the binding isotherms. Examination of these expressions leads to the conclusion that once initially bound, most multivalent ligands will be completely saturated by receptors and that partially bound species will be essentially nonexistent. This behavior is attributable to the generally high overall affinities of these ligands and to the mobility of the membrane‐bound species. Some specific comments are made, in light of this theory, about the binding of cholera toxin to its membrane receptor, the ganglioside

ISSN:0006-3525    

DOI:10.1002/bip.1981.360201104

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

年代:1981

数据来源: WILEY

摘要:

AbstractPublished data indicate linear variation of the duplex winding of DNA with logarithm of the ionic strength. We show that this observation is a natural prediction of a current poly‐electrolyte theory if structural coupling between duplex rotation angle (rotation per base pair) and step height (axial translation per base pair) is assumed. We show also that the coupling must then be negative: the positive winding on augmentation of the ionic strength must be accompanied by a decrement of step height, or axial compression. Cation species specificity of winding, CD spectra, and cation binding affinity are discussed in terms of local variation of dielectric shielding, using current accurate data for dielectric constants of aqueous salt solutions. One need not invoke specific complexation of cations, for which there is no present evidence (in aqueous solution), to explain any of these effects. The analysis is limited to low and moderate ionic strengths. Experimental observations at very high ionic strengths are puzzling and possibly conflicting. It is concluded that a need exists for systematic extension of available duplex winding data throughout the region of moderate to very high ionic strengths. It would be useful to extend the region at the low end as well, in order to distinguish clearly the behavior predicted by our model from that predicted by a referee on the basis of an alternate model described herei

ISSN:0006-3525    

DOI:10.1002/bip.1981.360201105

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

年代:1981

数据来源: WILEY

摘要:

AbstractThe Raman spectrum of polycytidylic acid was investigated in the pH range of 6.6–4.1. The thermal melting temperatures and the nature of the thermal melting profiles change in this range as monitored by the three Raman band envelopes, which include the 780‐, 805‐cm−1bands, the 1190‐, 1285‐cm−1bands, and the 1527‐cm−1band. By coupling these data with the theory of Raman scattering intensity and quantitative pH profiles for cytidine, it is shown that the band envelopes studied exhibit specific, yet different information regarding the thermal melting process. The band envelopes at 1170–1310 and 1527 cm−1, which are a sensitive function of both the extent of protonation and base stacking (hypochromic), revealTmvalues which agree with values derived from uv melting profiles. The 760–830‐cm−1envelope, which is not directly sensitive to cytosine residue protonation, but includes information associated with base stacking (the 780‐cm−1band) and the nature of the phosphodiester backbone (the frequency‐dependent 805‐cm−1component), exhibitsTmvalues which deviate from the values obtained from the other bands. The observed differences are pH‐dependent and correlate well with the extent of deprotonation that takes place in the denaturation process. Details of the spectrum of neutral and protonated poly(C) from pH 7 to 4.1 are discussed and related to the nat

ISSN:0006-3525    

DOI:10.1002/bip.1981.360201106

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

年代:1981

数据来源: WILEY

摘要:

AbstractTransient electric birefringence measurements of the rotational diffusion constant of five short restriction fragments of the plasmid pBR322 show that the hydrodynamic length is independent of sodium ion concentration in the range of 0.2 to 2.5 mM. The fragments are too stiff to be modeled as wormlike molecules. The rotational relaxation times of the fragments, which range from 64 to 124 base pairs, have been used to calculate the rise per base pair using six different theoretical expressions for the length dependence of the rotational diffusion coefficient of straight cylinder. The best estimate for the rise per base pair of Na‐DNA in solution is 3.3 ± 0.1

ISSN:0006-3525    

DOI:10.1002/bip.1981.360201107

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

年代:1981

数据来源: WILEY

摘要:

AbstractQuasielastic light scattering is used to study saline solutions of polyadenylic acid with varying polymer concentrations and molecular masses. These experiments clearly show the existence of two relaxation times. For dilute solutions, when the chains are mutually independent, the fast mode is due to the free diffusion of the polymer chains. For concentrations above the overlap concentrationC*, the fast mode is due to the propagation of collective excitations of the pseudolattice of polymer chains. The slow modes are observed when the polymer concentration is in the vicinity of the overlap concentrationC*. A series of experiments shows that both their relaxation time and amplitude depend only on the polymer concentration and not on the polymer molecular mass. This result rules out any previous explanation based on individual chain motion. Furthermore, since the amplitudes depend on the time elapsed from the preparation of the solution, the slow modes are due to the diffusion of concentration inhomogeneities in the pseudolattice.

ISSN:0006-3525    

DOI:10.1002/bip.1981.360201108

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

年代:1981

数据来源: WILEY

摘要:

AbstractThe absorption spectra and circular dichroism (CD) have been measured for aqueous solutions of acridine orange of a constant concentration, [D] = 5 × 10−5M, mixed with poly(S‐carboxyethyl‐L‐cysteine) in various mixing ratios, [P]/[D], ranging from 330 to 11, at different pH. The absorption spectra of the dye–polymer solutions are hypochromic, and the main band is located at 470 nm, accompanying a shoulder at 500 nm. At alkaline pH, no CD is induced in the visible region. At neutral and acidic pH, where the polymer is in the β‐conformation, CD is induced in the visible and near‐uv regions. A pair of CD bands is located at the region around 450 nm, when the pH is around the neutrality, while it appears at the region around 500 nm at acidic pH. Thus, the optically active species of bound dye changes from dimer to monomer on lowering the pH. These species form dissymmetric arrays along a polypeptide chain. The fraction of bound dye forming dissymmetric sequences is not high, but most of bound dye is adsorbed randomly on the ionized carboxyl groups of polypeptide chain and gives rise to hypochromism only. A dissymmetric structure of dye–polymer complexes is presented, in which the polymer has the β‐conformation and the dye cations, either dimeric or monomeric, bind to its side chains, in such a way that the longer axes of molecular planes of bound dye form a two‐fold, right‐handed helix along the extended polypeptide chain. A zeroth‐order calculation of CD based on the coupled oscillator model leads to the result that each dissymmetric array of dye consists, on the average, of two dimeric or monomeric cations. This low number of bound cations in a dissymmetric array and the large fraction of randomly adsorbed dye suggest that the hydrophobic interaction of dye with the polymer is strong, so that dye cations are adsorbed sparsely on both sides of the

ISSN:0006-3525    

DOI:10.1002/bip.1981.360201109

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

年代:1981

数据来源: WILEY

摘要:

AbstractTheoretical and practical advantages of neutron scattering for the determination of molecular weights of particles in solution are discussed. The method presented does not use known particles for calibration and is applicable to a wide molecular weight range (104–109); it is not sensitive to assumptions about the partial specific volume of the particles, and the experiments are performed quite easily in standard spectrophotometer cells using 100–500 μg of material. The method is nondestructive and the sample can be recovered totally. The use of D2O in solvents has particular advantages especially for multicomponent particles, for which thein situmolecular weight of each component can be determined separa

ISSN:0006-3525    

DOI:10.1002/bip.1981.360201110

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

年代:1981

数据来源: WILEY

摘要:

AbstractThe structure of water and its interaction energy with a fragment of B‐DNA composed of 12 base pairs and of the corresponding 24 sugar and 22 phosphate units and Na+ions (one at each phosphate group) are analyzed using Monte Carlo simulations. The sample of water molecules, at the simulated temperature of 300 K, is composed of 447 water molecules. The results are discussed either in terms of statistical analyses over the 2,000,000 simulated conformations (after equilibration) or with reference to an “average configuration.” Comparison is made to a simulation previously presented for the same system but without counterions. Isotherm at different relative humidity, hydration, and reactivity scales for different sites, the hydration number at each site, the structure of intraphosphate and interphosphate hydrogen‐bonded filaments of water are reported and discussed. The stabilization of the B‐conformation induced by the solvent with counterion (“ion‐induced compression effect”) is analyzed on the base of the above findings. A preliminary model to predict conformational transition in DNA is presented. The analyses reported are very detailed to allow refined interpretations of spectroscopic (infrared, Raman, and nmr) and scattering (x‐ray and neutron beam) data

ISSN:0006-3525    

DOI:10.1002/bip.1981.360201111

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

年代:1981

数据来源: WILEY