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  • Chemistry  (3)
  • 1990-1994  (3)
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  • 1
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The effect of elevated hydrostatic pressure on the secondary structure of poly(L-lysine) was studied using Fourier transform ir spectroscopy. According to changes observed in the amide I band, both the β-sheet and the unordered polypeptide undergo a reversible, pressure-induced conformational change to α-helix. The conversion occurs at a much higher pressure from the unordered conformer (∼ 9 kbar) than from the β-sheets (∼ 2 kbar). The structural changes were found to be slower at pH 〉 11, especially at the highest concentration investigated (10 wt%), reflecting the fact that extensive hydrogen-bond networks have to reorganize. This study shows that alterations of polypeptidic conformations induced by elevated hydrostatic pressure are reversible, but that an apparent irreversibility can result from kinetic factors in the case of conformational changes involving extensive rearrangements. The present results also show that the strength of the hydrogen bonds between the backbone amide groups is not the only factor that determines the closest packing of the polypeptide molecules.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    New York : Wiley-Blackwell
    Biopolymers 32 (1992), S. 1181-1186 
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The carboxylate-containing homopolypeptides poly(L-glutamate) [poly(Glu)] and poly(L-aspartate) [poly(Asp)] were found to form different types of ordered structures in the presence of poly(L-lysine) [poly(Lys)]. Mixing poly(Glu) with poly(Lys) in aqueous solution at neutral pH results in the instantaneous formation of a gel-like precipitate. The secondary structure of the gel precipitate can be best described as intermolecular antiparallel β-strands, involving the backbone amide groups, as evidenced by the presence of characteristic amide I bands in the ir spectrum at 1684 and 1612 cm-1. Mixing poly (Asp) with poly(Lys) under identical conditions results in the formation of a fine precipitate with a different morphology. Examination of the ir spectrum of the precipitate revealed that unlike poly(Glu), poly (Asp) did not yield any discrete secondary structure upon precipitation with poly(Lys). Addition of solutions containing Ca2+ or Mg2+ to the poly (Glu)/poly (Lys) aggregates resulted in complete dissolution of the gel, with the disappearance of the ir bands characteristic of the intermolecular hydrogen-bonded network. The results demonstrate the importance of salt bridges in establishing strong hydrogen bonds between the backbone amide groups. Reaggregation occurred upon heating the poly (Glu)/poly (Lys) mixture in the presence of Ca2+, but not in the presence of Mg2+ ions. In the presence of Ca2+ ions, aggregation and formation of an extended hydrogen-bonded network occurred upon heating. The aggregates formed upon heating poly (Glu)/poly (Lys) in the presence of Ca2+ were attributed solely to complexation of Ca2+ to the carboxylate groups of poly (Glu) with poly (Lys) remaining free in solution. Dissolution of the aggregate could be accomplished through addition of Mg2+ at room temperature. © 1992 John Wiley & Sons, Inc.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
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  • 3
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The structure of valinomycin in a range of organic solvents of varying polarity and in detergent and lipid dispersions has been studied by Fourier transform ir Spectroscopy. In solvents of low polarity such as chloroform, ir spectra of valinomycin are fully consistent with the bracelet structure proposed on the basis of nmr Spectroscopy, showing a single narrow amide I component attributable to the presence of β-turns and a single band arising from nonhydrogen-bonded ester C=O groups. K+ complexation results in a downward shift in the amide I band frequency, indicating an increase in the strength of the amide hydrogen bonds, along with a shift to lower frequencies of the ester C=O absorption due to a reduction in electron density in these bonds upon complexation. Identical results were obtained with NH4+, a finding not previously reported.In solvents of both medium (CHCl3/DMSO 3 : 1) and high (pure DMSO) polarity, we find evidence of significant disruption of the internal hydrogen-bonding network of the peptide and the appearance of a band suggesting the presence of free amide C=O groups. In such solvents, complexation with K+ and NH4+ was not observed.The structure of valinomycin in detergent micelles resembles that in nonpolar organic solvents. However, changes were found in the amide I and ester carbonyl maxima as 2H2O penetrated the micelle which suggest significant interaction between the solvent and peptide. Complexation with K+ was reduced in cationic detergent micelles as a result of a decrease in the effective K+ concentration due to charge repulsion at the micelle surface.In lipid bilayers the structure again appears identical to that found in chloroform. As in detergent micelles, the amide I and ester carbonyl bands exhibit shifts that indicate interactions with solvent. Complexation with both K+ and NH4+ is efficient, producing spectral changes similar to those seen in organic solvents.
    Additional Material: 8 Ill.
    Type of Medium: Electronic Resource
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