摘要:

Abstract13C spin‐lattice relaxation times of poly(L‐lysine) have been obtained at 67.9 MHz in aqueous solution and in a mixed solvent (40% methanol/60% water). A concomitant determination of the conformation by CD permits the correlation of conformation and rotational diffusion of the polymer. The dependence on pH of the spin‐lattice relaxation times of the13Cαand the side‐chain carbon resonances reflects the diffusional motion in the random‐coil conformation, in the helix–coil transition, and in the conformation of the α‐helix. In the mixed solvent the reorientational correlation time of the Cα‐Hαvector increases from τ = 0.37 nsec (random coil) to τ = 12.0 nsec (α‐helix). In aqueous solution the correlation time of this vector increases from τ = 0.33 nsec (random coil) to τ ≫ 11 nsec. The reorientation rates of the side‐chain methylene groups in the two solvents are markedly different. The reorientation of all methylene groups i

ISSN:0006-3525    

DOI:10.1002/bip.1980.360190902

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

年代:1980

数据来源: WILEY

摘要:

AbstractIn our earlier analysis of intermolecular interactions between collagen molecules, a major concern with the program employed is that it compared numbers of interactions between residues located on edges of defined, identical width and thus would not necessarily compare the same number of residues in each edge. This would be particularly true of some values of θ where well‐defined vertical ranking of residues occurs. We have examined ranking of residues in relation to intermolecular edge association between bovine skin [α1(I)]3model collagen molecules by utilizing two different methods of counting intermolecular interactions between residues. The interaction peaks at θ = 27.69° and 36.00° are absent or relatively less intense in the plots obtained by utilizing radial distances between interacting residues instead of vertical bands of defined width. These studies suggest caution in accepting recently reported analyses of superhelix coiling of the collagen molecule which point to values of 27.69° or 36.00° for the twist of the superhelix. Although intramolecular interactions clearly point to interaction of collagen molecules atDintervals, they are insufficiently restricted in distribution to provide a reliable estimate of the superhelix angle by procedures so far

ISSN:0006-3525    

DOI:10.1002/bip.1980.360190903

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

年代:1980

数据来源: WILEY

摘要:

AbstractRotational and wobbling diffusion coefficients for spherical and long‐chain molecules in membranes are calculated using a simple hydrodynamic model. Estimates of the contributions to the diffusion coefficients arising from hydrodynamic interactions between molecules and membrane interfaces are obtained and found to be small. For molecules containing polar head groups, we show that the presence of a membrane interface can produce a significant reduction in the wobbling diffusion coefficient over what would be obtained in an isotropic flui

ISSN:0006-3525    

DOI:10.1002/bip.1980.360190904

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

年代:1980

数据来源: WILEY

摘要:

AbstractThe solid‐state conformation of copolymers of β‐benzyl‐L‐aspartate [L‐Asp(OBzl)] withL‐leucine (L‐Leu),L‐alanine (L‐Ala),L‐valine (L‐Val), γ‐benzyl‐L‐glutamate [L‐Glu(OBzl)], or ϵ‐carbobenzoxy‐L‐lysine (Cbz‐L‐Lys) has been studied by ir spectroscopy and circular dichroism (CD). The ir spectra in the region of the amide I and II bands and in the region of 700–250 cm−1have been determined. The results from the ir studies are in good agreement with data obtained by CD experiments. Incorporation of the amino acid residues mentioned above into poly[L‐Asp(OBzl)] induces a change from the left‐handed into the right‐handed α‐helix. This conformational change for the poly[L‐Asp(OBzl)] copolymers was observed in the following composition ranges:L‐Leu, 0–15 mol %;L‐Ala, 0–32 mol %;L

ISSN:0006-3525    

DOI:10.1002/bip.1980.360190905

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

年代:1980

数据来源: WILEY

摘要:

AbstractThe probability of occurrence of helix and β‐sheet residues in 47 globular proteins was determined as a function of local hydrophobicity, which was defined by the sum of the Nozaki‐Tanford transfer free energies at two nearest‐neighbors on both sides of the amino acid sequence. In general, hydrophilic amino acids favor neither helix nor β‐sheet formations when neighbor residues are also hydrophilic but favor helix formation at higher local hydrophobicity. On the other hand, some hydrophobic amino acids such as Met, Leu, and Ile favor helix formation when neighbor residues are hydrophilic. None of the hydrophobic amino acids favor β‐sheet formation with hydrophilic neighbors, but most of them strongly favor β‐sheet formation at high local hydrophobicity. When the average of 20 amino acids is taken, both helix and β‐sheet residue probabilities are higher at higher local hydrophobicity, although the increase is steeper for β‐sheets. Therefore, β‐sheet formation is more influenced by local hydrophobicity than helix formation. Generally, helices are nearer the surface and tend to have hydrophilic and hydrophobic faces at opposite sides. The tendency of alternating regions of hydrophilic and hydrophobic residues in a helical sequence was revealed by calculating the correlation of the Nozaki‐Tanford values. Such amphipathic helices may be important in protein–protein and protein–lipid interactions and in forming hydrophilic channels in the membrane. The choice of 30 nonhomologous proteins as the data set d

ISSN:0006-3525    

DOI:10.1002/bip.1980.360190906

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

年代:1980

数据来源: WILEY

摘要:

AbstractThe nonlinear electrical properties of DNA solutions were measured when different monovalent cations were added to DNA. The influence of different parameters has been examined: fundamental frequency, field strength, and concentration. A linear relationship between the harmonic currentIhand the DNA concentration is shown, even for higher concentration values (400 mg/l.). The frequency dispersion ofIhhas the same shape for all the cations and the low‐frequency amplitude ofIhincreases in the following order: Li+

ISSN:0006-3525    

DOI:10.1002/bip.1980.360190907

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

年代:1980

数据来源: WILEY

摘要:

AbstractThe relative orientation of caffeine in stacks formed by self‐association in aqueous solution has been evaluated by both1H‐ and13C‐nmr spectroscopy. The data, which were interpreted through the calculation of ring‐current and atomic diamagnetic anisotropic effects of the caffeine molecule, suggest two caffeine bases may stack in a nearly orthogonal manner. The interactions between caffeine and adenylyl‐3′,5′‐adenosine, polyadenylic acid, and ribo‐(A‐A‐G‐C‐U‐U)2helix were also studied by nmr at different caffeine/base ratios and at varying temperatures. The results show that caffeine tends to stack on the top of the terminal purine bases or to insert (the single‐stranded) or to intercalate (the double

ISSN:0006-3525    

DOI:10.1002/bip.1980.360190908

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

年代:1980

数据来源: WILEY

摘要:

AbstractQuasielastic light scattering methods were used to study calf thymus DNA in solutions of LiCl, NaCl, NH4Ac, and NH4Cl. Plots of the reciprocal relaxation time (1/τ) vs sin2(θ/2), where θ is the scattering angle, exhibit two linear regions, in accordance with theories for semiflexible polymers based on thet→ 0 approximation. In these theories the slope of the linear region at low angles is associated with the translational diffusion coefficient (Dt), whereas the slope of the linear region at high angles is associated with the segmental diffusion coefficient (Ds=kT/ƒs). The midpoint of the “transition” between these two linear regions is associated with the mean displacement between segments (b). Data presented here indicate that the Rouse‐Zimm parametersband ƒsare significantly different for DNA in 0.4MNH4Cl relative to the other salts at comparable ionic strengths. It is suggested that this difference reflects local solvent structure and that bothbandDsare sensitive to the local wat

ISSN:0006-3525    

DOI:10.1002/bip.1980.360190909

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

年代:1980

数据来源: WILEY

摘要:

AbstractDry purified ligamentum nuchae elastin has been investigated for physical aging. The samples were quenched from a temperature (197°C) close to the softening point to a number of measuring temperatures ranging from −20 to +180°C. At each temperature, the small‐strain torsional creep properties were determined at a number of elapsed intervals after the quench. Aging effects were found over the whole temperature range, and the creep and aging behavior of elastin turned out to be very similar to that of synthetic pol

ISSN:0006-3525    

DOI:10.1002/bip.1980.360190910

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

年代:1980

数据来源: WILEY

摘要:

AbstractThe optical rotation and the conductivity of kappa‐carrageenans in aqueous solution have been investigated as functions of temperature in the presence of various electrolytes. The activity coefficients of sodium and potassium have been determined and correlated with the conformation. The potassium activity coefficient under ordered conformation is in agreement with a mechanism of dimerizatio

ISSN:0006-3525    

DOI:10.1002/bip.1980.360190911

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

年代:1980

数据来源: WILEY