摘要:

AbstractThe difference between the theories of Manning, on the one hand, and of Odijk and Skolnick and Fixman, on the other, for the polyelectrolyte contribution to the persistence length of DNA is shown to arise entirely from a subtle geometrical error in the theory of Manning. The corrected theory of Manning predicts a negligible polyelectrolyte contribution in 1.0MNaCl and only 33 Å in 0.01MNaCl, thus giving a change in total persistence length by a factor of only 1.07 over that range, in agreement with Odijk. Pertinent data in the literature indicate that the persistence length must change by a factor of ≤ 1.6 between 1.0 and 0.01MNaCl, and very likely by less than a factor of 1.4. Evidently, the intrinsic rigidity of the uncharged double‐strand filament dominates the bending rigidity at NaCl concentrations above 0

ISSN:0006-3525    

DOI:10.1002/bip.1981.360200202

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

年代:1981

数据来源: WILEY

摘要:

AbstractA conformational quantum‐mechanical study of (Gly‐Phe‐Pro) and (Gly‐Pro‐Phe) repeating tripeptide sequences has been carried out with the PCILO method. Using appropriate molecules as a model, we investigated the conformational possibilities of eachin situresidue. Computations have been done taking into account the two typical pyrrolidine ring puckering and the most favorable orientations of the phenylalanyl side chain. Major conclusions drawn from this study are that the phenylalanyl can be accommodated at both second and third positions in the sequence without preventing the formation of triple‐helix conformation. However, the analogy observed between the rotational possibilities around the second residue of Gly‐Pro‐Pro and Gly‐Phe‐Pro indicates that phenylalanyl in the second position favors the tri

ISSN:0006-3525    

DOI:10.1002/bip.1981.360200203

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

年代:1981

数据来源: WILEY

摘要:

AbstractThe crystal structures ofL‐3,4‐dehydroproline,t‐butoxycarbonyl‐L‐3,4‐dehydroproline amide, and acetyl‐L‐3,4‐dehydroproline amide have been determined.L‐3,4‐Dehydroproline is orthorhombic witha= 16.756,b= 5.870,c= 5.275 Å, andZ= 4;t‐butoxycarbonyl‐L‐3,4‐dehydroproline amide is orthorhombic witha= 6.448,b= 8.602,c= 21.710 Å, andZ= 4; acetyl‐L‐3,4‐dehydroproline amide is monoclinic witha= 4.788,b= 10.880,c= 7.785 Å, β = 105.25°, andZ= 2. The finalRvalue for theL‐3,4‐dehydroproline is 0.046 based on 529 reflections; fort‐butoxycarbonyl‐L‐3,4‐dehydroproline amide, 0.050 based on 792 reflections; and for acetyl‐L‐3,4‐dehydroproline amide, 0.058 based on 632 reflections. The structures clearly establish that the free amino acid exists in the zwitterionic form in the crystalline state. The molecular conformations of thet‐Boc and acetyl derivatives consist of two planes: one involving the primary amide and the other the remaining atoms of the molecule. The acetyl‐L‐3,4‐dehydroproline amide contains a tertiary amide bond in thecisconformation. To the best of our knowledge, this is the first example of acisbond in an acetyl derivative of an amino acid or peptide. At variance with the previously reported proline amides, which present ϕ and ψ values corresponding to those of a right‐handed α‐helical conformation (conformation A), thet‐Boc and acetyl derivatives both have

ISSN:0006-3525    

DOI:10.1002/bip.1981.360200204

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

年代:1981

数据来源: WILEY

摘要:

AbstractWe consider six‐dimensional diffusion and frictional tensors for a rigid macromolecule immersed in a viscous fluid at low Reynolds number. Our treatment allows for screwlike properties which couple rotational and translational movements. We show that the center of diffusion of a screwlike body can be distinct from its hydrodynamic center of reaction. Symmetry conditions which ensure coincidence are examined. The center of diffusion is found to be the point of a body with the slowest diffusive movements, while rotations about the center of reaction encounter the least average resistance. The macroscopic translational diffusion coefficient is evaluated from a perturbation analysis of the six‐dimensional diffusion equation. We show that methodologies which ignore translational–rotational coupling will necessarily underestimate the diffusion rate of screwlike particles. A procedural framework is presented to calculate diffusion coefficients of complicated bodies. As an example we treat a long ben

ISSN:0006-3525    

DOI:10.1002/bip.1981.360200205

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

年代:1981

数据来源: WILEY

摘要:

AbstractThe structure of the nucleosome core particle in solution has been studied by neutron scattering using the full‐contrast variation technique, which reduces the experimental spectra to three fundamental scatter functions holding information on shape and structure. Systematic calculations of the fundamental scatter functions expected from proposed core‐particle models have been compared with the observed functions and show that the neutron‐scattering criteria severely restrict the number of models which can be valid for the structure in solution. The best model for the core particle in solution has a hydrophobic histone core about which 1.7 ± 0.1 turns of DNA are wrapped at a pitch between 3.0 and 3.5 nm. This core contains most of the histone and has an average thickness of 4 nm and diameter 6.4–7.5 nm. While solution scattering is not able to specify uniquely the actual shape of the core to high resolution, all models which are possible for the shape of the core to a resolution justified by the data have been considered. It is clear that cylindrical or wedge shapes compatible with the above dimensions are valid structures. A hole probably penetrates the histone core, but the data do not allow a diameter greater than 1 nm. Available evidence suggests that about a quarter of the total histone is outside

ISSN:0006-3525    

DOI:10.1002/bip.1981.360200206

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

年代:1981

数据来源: WILEY

摘要:

AbstractIn carbonate buffer at pH 10.5, a transparent solution of poly(L‐lysine HBr) was obtained up to fairly high concentration of 3 g/dl at room temperature. The hydrodynamic behavior of the solution has been studied by sedimentation analyses and viscosity measurements. A dimer form for high concentrations and a monomer form for low concentrations were inferred. The dimer and monomer forms were assigned to a β‐structure and α‐helix, respectively, based on the CD and optical rotary dispersion spectra. Using CD spectroscopy, a reversible transition between α‐helix and β‐structure was observed as a function of either poly(L‐lysine HBr) concentration or temperature. An aggregated form which was assigned to the antiparallel pleated sheet appeared at 50°C on the basis of

ISSN:0006-3525    

DOI:10.1002/bip.1981.360200207

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

年代:1981

数据来源: WILEY

摘要:

AbstractThe structure of thermally denatured Type I collagen has been studied using laser light scattering. The results indicate that the diffusion coefficients of α‐chains and β‐ and γ‐components are 1.550 ± 0.08 × 10−7, 1.000 ± 0.05 × 10−7, and 0.835 ± 0.04 × 10−7cm2/sec, respectively, at temperatures between 20 and 40°C. It is concluded from diffusion data that these species have hydrodynamic radii of about 13.8 nm (α‐chain), 21.5 nm (β‐component), and 25.7 nm (γ‐component), consistent with previous studies of thermal denaturation by light scattering. It is also concluded, based on volume calculations, that a large volume increase occurs when the triple helix unfolds. Homodyne correlation functions for two component mixtures of α‐chains and β‐and γ‐components appeared to decay exponentially. In all but one case discussed the correlation function could be fitted with a single component having a translational diffusion coefficient which was an intensity weighted average of the diffusio

ISSN:0006-3525    

DOI:10.1002/bip.1981.360200208

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

年代:1981

数据来源: WILEY

摘要:

AbstractThe circular dichroism (CD) and1H‐nmr properties of peptide 401, a bee venom component with 22 amino acid residues and two disulfide bridges, have been studied under a variety of conditions and compared with those of the structurally related octadecapeptide apamin. The major component of the relatively intense CD signal in the 200–230‐nm region in both cases probably arises from the rigid asymmetric ring structures of the disulfide bridges. CD spectra are practically unaffected by pH (in the region 1–7), solvent (water, trifluoroethanol, dioxane/water mixtures), concentration of peptide, or additions of salt (guanidinium chloride, KCl). Temperature changes (in the range 20–59°C) have only a modest influence. For both apamin and peptide 401, reduction of the two disulfide bridges results in a dramatic change of the CD spectrum, which acquires the characteristic form of a random coil. Preliminary1H‐nmr data are presented for both the reduced and the oxidized form. Several resonance peaks could be assigned on the basis of the theoretical random‐coil spectrum. In the oxidized forms, six slowly exchangeable amide protons could be found in a spectrum taken at low pH, which are ascribed to intramolecular hydrogen bonds. Each of the four protons of the two histidine residues of peptide 401 appears as two distinct resonance peaks in the oxidized form but not in the reduced form. This is interpreted as arising from conformational heterogeneity

ISSN:0006-3525    

DOI:10.1002/bip.1981.360200209

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

年代:1981

数据来源: WILEY

摘要:

AbstractCircular dichroic spectra and oscillator strengths of the π‐π transition near 190 nm are calculated for helical (Gly)6and (Ala)6at 30° intervals of the backbone torsion angles (ϕ,ψ) over the range ‐180° ≤ ϕ ≤ ‐60°, −60° ≤ ψ ≤ 180°, using the partially dispersive normal mode treatment of the dipole interaction model. Polarizabilities of atoms and the NC′O group are those determined semiempirically in previous studies. Calculations for (Ala)6at (ϕ,ψ) angles corresponding to the α‐helix, the poly(Pro) II helix, a collagen single helix, a poly‐(MeAla) helix, and single β‐helices are found to agree well with m

ISSN:0006-3525    

DOI:10.1002/bip.1981.360200210

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

年代:1981

数据来源: WILEY

ISSN:0006-3525    

DOI:10.1002/bip.1981.360200201

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

年代:1981

数据来源: WILEY