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  • 1
    Electronic Resource
    Electronic Resource
    Molecular organization of glycophorin A: Implications for membrane interactions (1985)
    New York : Wiley-Blackwell
    Biopolymers 24 (1985), S. 2301-2332 
    Details
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Physical studies and conformational analysis of human glycophorin A suggest a revised model for its molecular organization, self-association, and interactions with the erythrocyte membrane. Intrinsic viscosity has been used to study, under more physiological conditions, the monomer-dimer equilibrium demonstrated previously by polyacrylamide-SDS gel electrophoresis. The results show that the equilibrium persists in the absence of detergent and support earlier indications that the dimer is probably the physiologically relevant form and that it is promoted by salt, inhibited by conventional denaturants, and abolished by carboxymethylation.Combined application of CD, fitted to the poly-(L-lysine) model spectra of Greenfield and Fasman, and conformational prediction, by the statistical method of Chou and Fasman and the stereochemical approach of Lim, suggests five helical sequences in glycophorin A: Arg-39 to Tyr-52 (A); Gln-63 to Glu-70 (B); Glu-72 to Leu-89 (C); Ile-95 to Lys-101 (D); and Leu-118 to Asn-125 (E). Sequence A occurs only at low pH and may be stabilized by favorable noncovalent interactions of O-linked tetrasaccharide side chains. The other four helices all occur in the dimeric form of glycophorin A at physiological pH and ionic strength. Sequence D is destroyed by trypsin, and is also lost on conversion to the monomeric form of the glycoprotein at low ionic strength. Sequence E is denatured by 6M guanidine hydrochloride/4M urea. Sequences B and C, which are separated by a single proline residue, are stable under all these conditions.Dimerization of the major, hydrophobic helical sequence, (C) may be promoted and directed by an adjacent short sequence of intermolecular parallel β-sheet (Leu-90 to Tyr-93). It is proposed that these two structures span the lipid bilayer in vivo, and that helices B and D lie, respectively, along the outer and inner surfaces of the membrane. Molecular organization in the N- and C-terminal regions of the molecule is discussed in terms of evidence from the present work and from other recent investigations.
    Additional Material: 16 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/bip.360241210
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  • 2
    Electronic Resource
    Electronic Resource
    Crystallization of polyethylene at elevated pressures (1971)
    New York : Wiley-Blackwell
    Journal of Polymer Science Part A-2: Polymer Physics 9 (1971), S. 385-406 
    Details
    ISSN: 0449-2978
    Keywords: Physics ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The crystallization from the melt of three sharp polyethylene fractions has been studied at 5 kbar. It has been shown that the thickness of so-called extended-chain lamellae is a function of time, temperature, and molecular weight. There is by no means just the fully extended molecular configuration present. Crystallization is qualitatively similar to that of chain-folded crystals at 1 bar, giving an optimum lamellar thickness which increases with time and decreasing supercooling. Fractional crystallization is widespread and is a major cause of disparate lamellar thickness. Isothermal thickening of lamellae during crystallization has been established directly. Morphological detail suggests further that layers can increase their thickness tenfold over their initial size.
    Additional Material: 14 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pol.1971.160090301
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  • 3
    Electronic Resource
    Electronic Resource
    Total optical activity of agarose: Relation to observable transitions in the vacuum ultraviolet (1986)
    New York : Wiley-Blackwell
    Biopolymers 25 (1986), S. 959-973 
    Details
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The changes in optical activity that accompany and characterize the coil-helix and helix-coil transitions of agarose in aqueous solutions and gels have been investigated by combined quantitative analysis of data from vacuum ultraviolet circular dichroism (VUCD) and optical rotary dispersion (ORD). VUCD of agarose in the high-temperature coil state shows a single accessible Gaussian band centered at ∼183 nm. In the helix state this band is blue-shifted by ∼9 nm, and the intensity is increased by a factor of ∼2.6. Spectra at intermediate temperatures can be fitted to within experimental error by linear combination of coil and helix spectra, the relative proportions required providing an index of the extent of conformational ordering. ORD spectra throughout the conformational transition have a common form and differ only in absolute magnitude. The temperature course of conformational ordering derived from ORD intensity is in close agreement with the values obtained from VUCD. In both the coil and helix states the accessible VUCD band is positive, while the overall ORD is negative, indicating strong negative CD activity at lower wavelength. The ORD contribution corresponding to the positive VUCD band was calculated by Kronig-Kramers transform, and it was subtracted from the total ORD to give the residual ORD from all other optically active transitions of the molecule. In both the coil and helix states, this residual ORD could be fitted to within experimental error by a single Gaussian CD band at ∼149 nm. A negative band at this wavelength has been reported previously for agarose films, but the observed intensity, relative to that of the lower energy positive band, is substantially smaller than the fitted value under hydrated conditions. In both the coil and helix states the total optical activity of agarose, characterized by observed ORD spectra, can be matched to within experimental error by Kronig-Kramers transform of the 149-nm negative band and the smaller positive band at higher wavelength, with no necessary involvement of deeper-lying transitions. The significance of this conclusion for fundamental understanding of carbohydrate optical activity is discussed.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/bip.360250514
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  • 4
    Electronic Resource
    Electronic Resource
    Dynamics of molecular organization in agarose sulphate (1986)
    New York : Wiley-Blackwell
    Biopolymers 25 (1986), S. 1009-1029 
    Details
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Nongelling solutions of structurally regular chain segments of agarose sulphate show disorder-order and order-disorder transitions (as monitored by the temperature dependence of optical rotation) that are closely similar to the conformational changes that accompany the sol-gel and gel-sol transitions of the unsegmented polymer. The transition midpoint temperature (Tm) for formation of the ordered structure on cooling is ∼25 K lower than Tm for melting. Salt-induced conformational ordering, monitored by polarimetric stopped-flow, occurs on a millisecond time scale, and follows the dynamics expected for the process 2 coil ⇌ helix. The equilibrium constant for helix growth (s) was calculated as a function of temperature from the calorimetric enthalpy change for helix formation (ΔHcal = -3.0 ± 0.3 kJ per mole of disaccharide pairs in the ordered state), measured by differential scanning calorimetry. The temperature dependence of the nucleation rate constant (knuc), calculated from the observed second-order rate constant (kobs) by the relationship kobs = knuc(1 - 1/s) gave the following activation parameters for nucleation of the ordered structure of agarose sulphate (1 mg mL-1; 0.5M Me4NCl or KCl): ΔH* = 112 ± 5 kJ mol-1; ΔS* = 262 ± 20 J mol-1 K-1; ΔG*298 = 34 ± 6 kJ mol-1; (knuc)298 = (7.5 ± 0.5) × 106 dm3 mol-1 s-1. The endpoint of the fast relaxation process corresponds to the metastable optical rotation values observed on cooling from the fully disordered form. Subsequent slow relaxation to the true equilibrium values (i.e., coincident with those observed on heating from the fully ordered state) was monitored by conventional optical rotation measurements over several weeks and follows second-order kinetics, with rate constants of (2.25 ± 0.07) × 10-4 and (3.10 ± 0.10) × 10-4 dm3 mol-1 s-1 at 293.7 and 296.2 K, respectively. This relaxation is attributed to the sequential aggregation processes helix + helix → dimer, helix + dimer → trimer, etc., with depletion of isolated helix driving the much faster coil-helix equilibrium to completion. Light-scattering measurements above and below the temperature range of the conformational transitions indicate an average aggregate size of 2-3 helices.
    Additional Material: 10 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/bip.360250604
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  • 5
    Electronic Resource
    Electronic Resource
    Spectroscopic origin of conformation-sensitive contributions to polysaccharide optical activity: Vacuum-ultraviolet circular dichroism of agarose (1979)
    New York : Wiley-Blackwell
    Biopolymers 18 (1979), S. 327-333 
    Details
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The vacuum-uv CD of agarose solid films has been measured to 145 nm and shows a positive band near 180 nm and a larger negative band at around 152 nm. The positive band remains accessible in aqueous solution and has been used to characterize changes in molecular conformation and interaction during the sol-gel transition. The temperature profile of vacuum-uv CD shows sharp, discontinuous changes around the melting and setting points of the gel, which are interpreted in terms of cooperative intermolecular association through double helices, and pronounced hysteresis, which is discussed in terms of helix-helix aggregation.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/bip.1979.360180209
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  • 6
    Electronic Resource
    Electronic Resource
    Tyrosine optical activity as a probe of the conformation and interactions of fibronectin (1983)
    New York : Wiley-Blackwell
    Biopolymers 22 (1983), S. 821-831 
    Details
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A very intense negative band is observed at ∼ 183 nm in the CD spectrum of fibronectin from bovine plasma. This transition has not previously been reported, probably because it occurs in a spectral region that has not been readily accessible in earlier studies. At longer wavelength, the observed CD is very similar to spectra reported for human and chick material, having positive bands at ∼230 and ∼200 nm, and a negative band at ∼215nm. The low molar ellipticity of the negative band ([θ] ≈ -2.5 × 103 deg cm2 dmol-1) suggests little α-helix or β-sheet structure. The new transition, and the two positive bands at higher wavelength, do not correspond to known transitions of the peptide backbone, but all three are present in the CD of N-acetyltyrosineamide. It is therefore suggested that the observed CD behavior of fibronectin arises predominantly from the optical activity of tyrosine side chains. The contribution of this side-chain optical activity to the CD of other proteins is discussed.On raising pH to ionize tyrosine residues, the positive CD band at ∼230 nm is lost in both N-acetyltyrosineamide and in fibronectin. The spectral change is fully reversible in the model compound, but only partially reversible in fibronectin. From this evidence, and the magnitude of the 183-nm band, it is suggested that some or all of the tyrosine residues in fibronectin may be present within ordered domains. The possible role of S—S bonds in maintaining tertiary structure is discussed. The interaction of fibronectin with heparin is accompanied by a large increase in the 183-nm band and by slight enhancement of the negative band at 215 nm, consistent with some limited formation of β-sheet.Present results indicate that CD may be of considerable value in characterization of the molecular organization and biologically relevant interactions of fibronectins and of related glycoproteins of the extracellular matrix.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/bip.360220305
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  • 7
    Electronic Resource
    Electronic Resource
    Peptide-bond distortions and the curvature of α-helices (1986)
    New York : Wiley-Blackwell
    Biopolymers 25 (1986), S. 1087-1093 
    Details
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Solvent accessible peptide bonds in proteins exhibit a 1-3° compression of the OCN bond angle and a corresponding expansion of the NCCa bond angle, relative to buried peptide bonds. These changes are consistent with an increase in hydrogen bonding to the carbonyl oxygen accompanying solvent exposure (J. D. Dunitz and F. K. Winkler, (1975) Acta Cryst. B31, 251-263). For amphiphilic structures such as α-helices, systematic differences in peptide-bond geometry between solvent-exposed and buried residues will generate significant curvature. A decrease of 4° in the OCN bond angle between hydrophilic and hydrophobic sides of an amphiphilic helix will lead to smooth bending, with a radius of curvature of about 70 Å. This curvature is in the range observed for α-helices in proteins. Helix curvature is estimated to have only a small effect on the magnitude and direction of the helical dipole moment.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/bip.360250609
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  • 8
    Electronic Resource
    Electronic Resource
    Molecular origin of xanthan solution rheology: Effect of urea on chain conformation and interactions (1982)
    New York : Wiley-Blackwell
    Journal of Polymer Science: Polymer Letters Edition 20 (1982), S. 531-538 
    Details
    ISSN: 0360-6384
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pol.1982.130201004
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  • 9
    Electronic Resource
    Electronic Resource
    On the formation of extended-chain lamellae in polyethylene (1969)
    New York : Wiley-Blackwell
    Journal of Polymer Science Part B: Polymer Letters 7 (1969), S. 273-280 
    Details
    ISSN: 0449-2986
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pol.1969.110070406
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