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  • 1
    Electronic Resource
    Electronic Resource
    Springer
    European biophysics journal 22 (1993), S. 279-288 
    ISSN: 1432-1017
    Keywords: Gramicidin A ; Ion channel ; Membrane proteins ; FTIR ; Circular dichroism
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Physics
    Notes: Abstract The structure of the channel-forming polypeptide gramicidin A (GA) incorporated into phosphatidylcholine (PC) liposomes has been studied as a function of the degree of unsaturation of the acyl chains of PC. The initial conformational state of GA in reconstituted bilayers is determined by the solvent in which the peptide and the lipid are initially co-dissolved, whereas the equilibrium conformational state (after heat incubation) is affected by the lipid structure rather than by the nature of the solvent. The conformational equilibrium of GA has been studied in liposomes prepared from PC having a variable number of double bonds in the fatty acid moiety, by circular dichroism and Fourier transform infrared. Liposomes were prepared from trifluoroethanol or ethanol solutions and incubated at 68°C. GA was shown to retain the conformation of the right-handed π $$\overleftarrow 6$$ .3 π $$\overrightarrow 6$$ .3 helix in PC with saturated acyl chains and with one double bond, whereas in dilinoleoyl-PC, having two double bond in each chain, the thermodynamically preferred structures are left-handed antiparallel and parallel double ππ5.6 helices. Natural soybean PC also favours left-handed ππ5.6 helical structures of GA (≈75%). This finding is discussed in terms of the role of PC unsaturation in the dynamic properties of the lipid matrix. Differences between observed FTIR spectra of the ↑↓ππ=5.6 helix in solution (and to a larger extent in the membrane) and the calculated IR spectra can be interpreted as resulting from deviation of the real structure from the theoretically derived ideal helix. The data obtained provide grounds for better understanding of a GA channel functioning in lipids of variable degrees of unsaturation.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 0570-0833
    Keywords: Depsipeptides ; Peptides ; Topochemistry ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The basic principles of the topochemical approach to the investigation of the structure-function relation in peptide systems are formulated. This approach makes use of the new possibility of transforming natural peptides, consisting in the modification of the molecule as a whole and utilization of the resultant analogs to elucidate the boundaries of the stereoelectronic complementarity of the biologically active peptide to the corresponding receptor. In particular, on the example of depsipeptide antibiotics and their topochemical analogs the fruitfulness of using such compounds as tools in elucidating the physicochemical basis of functioning of biological membranes is shown. The topochemical principle has also been applied in preparing specific competitive inhibitors of proteolytic enzymes, whose study may shed light on the nature of the forces binding the substrate to the contact site of the corresponding enzyme.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
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