ISSN:0006-3525    

DOI:10.1002/bip.360241102

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

年代:1985

数据来源: WILEY

ISSN:0006-3525    

DOI:10.1002/bip.360241103

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

年代:1985

数据来源: WILEY

ISSN:0006-3525    

DOI:10.1002/bip.360241104

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

年代:1985

数据来源: WILEY

摘要:

AbstractNmr and CD studies of terminally protected tetrapeptides were carried out in aqueous and DMSO solutions to investigate the formation and stabilization of the β‐turn structure. Boc‐Gly‐Lys‐Asp‐Gly‐OMe and Boc‐Asp‐Lys‐Asp‐Gly‐OMe appear to have a tendency to adopt a β‐turn structure in aqueous solution from the CD spectra and temperature‐dependence studies of the amide proton chemical shifts. The side‐chain conformation of the Asp residue depends greatly on its ionization state but was not affected by the deprotonation of the neighboring Lys side chain. There is evidence for an intramolecular interaction between the Asp and Lys side chains of Boc‐Gly‐Lys‐Asp‐Gly‐OMe. Such an interaction can contribute to th

ISSN:0006-3525    

DOI:10.1002/bip.360241105

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

年代:1985

数据来源: WILEY

摘要:

AbstractA theory of adsorption of a polypetide chain capable of undergoing the coil–β‐structure transition on a solid planar surface has been developed. The mutual influence of two order–disorder phase transitions, a conformational and an adsorption transition, was investigated. Various types of adsorption transitions are possible, depending on the initial conformational state (partly or completely β‐structured) and the selectivity of adsorption: (a) the second‐order phase transition, in which the chain is partly structured, both in adsorbed and desorbed states; and (b) the first‐order phase transition, in which the chain exhibits a regular β‐structure, at least on one side of the adsorption transition boundary. The chain bonding to the surface alters the degree of β‐structure, both in the case of selective and nonselective adsorption (similar to the adsorption of the chains with other types of secondary structure). We show that the slope of the adsorption curves for partly β‐structural chains increases as a result of an increase in the degree of β‐structuring, and this effect is even stronger than the analogou

ISSN:0006-3525    

DOI:10.1002/bip.360241106

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

年代:1985

数据来源: WILEY

摘要:

AbstractThe conformation of phenylacetyl‐D‐alanyl‐D‐alanine in the crystalline state was characterized by Fourier‐transform ir and Raman spectroscopy and was unambiguously solved by x‐ray single‐crystal determination. In the crystalline state, the molecule adopts a partially folded conformation quite similar to that of another cell wall peptide, acetyl‐D‐alanyl‐D‐alanine [Benedetti et al. (1981)J. Biol. Chem.256, 9229–9234], although the crystal structure is stabilized by a quite different intermolecular hydrogen‐bond pattern. No significant deviation from the usualtrans‐planar peptide group geometry was detected. The conformations accessible in the noncrystalline state were investigated by ir measurements in solution and conformational energy calculations. The theoretical study revealed that the peptide is a highly flexible molecule, since 55 minima were detected, within 3 kcal/mol, including the conformation found in the single crystal. The ir data for phenylacetyl‐D‐alanyl‐D‐alanine in different solvents were in accordance with virtually extended conformations, with some indication for weak, intramolecularly hydrogen‐bonded C5‐rings. These conformational data obtained for the cell wall peptide analog are compared with those known fo

ISSN:0006-3525    

DOI:10.1002/bip.360241107

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

年代:1985

数据来源: WILEY

摘要:

AbstractVarious copolypeptides were prepared by benzylamine or tertiary amine‐initiated copolymerizations of alanine–N‐carboxyanhydride (Ala‐NCA) and valine–N‐carboxyanhydride (Val‐NCA). The number‐average molecular weights of these copolypeptides were detemined by1H‐nmr spectroscopic end‐group analyses and viscosity measurements. The sequences were characterized by15N‐nmr spectra in solution, and the average lengths of the homogeneous blocks were determined from the signal intensities. The 50.3‐and 75.4‐MHz13C‐nmr CP/MAS spectra of the solid copolypeptides are not sensitive to sequence effects, but allow qualitative and quantitative analyses of the secondary structures. In contrast to other methods, the13C‐nmr spectra allow determination of the extent to which individual amino acids are incorporated into β‐sheet or α‐helix phases. Depending on primary structure and molecular weight, the secondary structure of (Ala/Val) copolypeptides may vary significantly. Both monomer units may be predominantly helical or predominantly β‐sheet structure, or the Val units may prefer the β‐sheet structure with most Ala‐units forming β‐helices. However, these secondary structures are more or less thermodynamically unstable and revert to the stable conformations on r

ISSN:0006-3525    

DOI:10.1002/bip.360241108

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

年代:1985

数据来源: WILEY

摘要:

AbstractThe free fractions of monovalent and divalent counterions were determined on salt‐free solutions of pectins. The effects of charge density, distribution of the carboxyl groups, polymer concentration, and the nature of the counterion were investigated by determinating the calcium and sodium activity coefficients (with specific electrodes) and by measuring the transport parameters (by conductimetry). Poor agreement for calcium ions was found with the Manning theory. The strong binding of these ions to highly charged polymers, which is ascribed to a dimerization process was demonstrated in very dilute solution

ISSN:0006-3525    

DOI:10.1002/bip.360241109

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

年代:1985

数据来源: WILEY

摘要:

AbstractThe translational and rotational diffusion coefficients have been calculated for a simple, segmentally flexible model: the hinged dumbbell (HD). In the HD, two spherical subunits are attached to an universal joint by means of frictionless connectors. In addition to the case in which hydrodynamic interactions are neglected (NI), we have also considered two more cases, including hydrodynamic interaction by means of the Kirkwood‐Riseman approximate treatment (KR) and using accurate procedure based in the series expansions for the two‐sphere diffusion tensor (SE). Expressions for the friction coefficients of the HD are given for the three cases, and the diffusion coefficients are evaluted inverting the 9 × 9 resistance matrix, for two HDs with different dimensions. The KR treatment, which includes a contribution from the finite volume of the subunits, is shown to be an excellent approximation to the more rigorous procedure. In the NI case for rotation, the various coefficients present different deviations with respect to the SE results. A rough estimate of the errors of the NI relaxation times indicates that they may be smaller than 15% for a HD with identical beads. However, the influence of hydrodynamic interaction should be more important for the rotational diffusivity of a small sphere attached to a larger one. The error of the NI result for the translational diffusion coefficient is of about 25% for the two

ISSN:0006-3525    

DOI:10.1002/bip.360241110

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

年代:1985

数据来源: WILEY

摘要:

AbstractThe mutual diffusion coefficient of the bovine nasal cartilage proteoglycan subunit is found to increase rapidly with increasing concentration and decreasing ionic strength. These results have been obtained by analysis of the boundary relaxation of concentration gradients in the analytical ultracentrifuge by schlieren optics. The diffusion behavior can be understood in terms of the nonideality of the proteoglycan. The magnitude of the nonideality is dominated by charge interactions, whereas the influence of molecular size and associated excluded‐volume interactions is small. The concentration dependence of the apparent diffusion coefficient of the proteoglycan subunit from dynamic light scattering was found, in contrast, to decrease with increasing concentration. Computer simulation of the dynamic light scattering suggests that the presence of a small population of aggregates may account for the difference in the two types of diffusion measurement due to their marked influence on the scatterin

ISSN:0006-3525    

DOI:10.1002/bip.360241111

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

年代:1985

数据来源: WILEY