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Oxidation-state-dependent reactions of cytochrome c with the trioxidocarbonate(•1−) radical: a pulse radiolysis study

Domazou, Anastasia ; Koppenol, Willem

In: JBIC Journal of Biological Inorganic Chemistry, 2007, vol. 12, no. 1, p. 118-125

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    Titre
    • Oxidation-state-dependent reactions of cytochrome c with the trioxidocarbonate(•1−) radical: a pulse radiolysis study
    Auteur
    • Domazou, Anastasia. Institute of Inorganic Chemistry, Department of Chemistry and Applied Biosciences, Swiss Federal Institute of Technology, ETH Zurich, Wolfgang-Pauli-Strasse 10, 8093, Zurich, Switzerland
    • Koppenol, Willem. Institute of Inorganic Chemistry, Department of Chemistry and Applied Biosciences, Swiss Federal Institute of Technology, ETH Zurich, Wolfgang-Pauli-Strasse 10, 8093, Zurich, Switzerland
    Type de document
    • Postprint
    Langue
    • Anglais
    Publié dans
    • JBIC Journal of Biological Inorganic Chemistry, 2007, vol. 12, no. 1, p. 118-125. Springer-Verlag
    Autre version électronique
    Identifiant OAI-PMH
    • oai:doc.rero.ch:320427
    Summary
    The reaction of the trioxidocarbonate(•1−) radical (CO 3 •− , "carbonate radical anion”) with cytochrome c was studied by pulse radiolysis at alkaline pH and room temperature. With iron(III) cytochrome c, CO 3 •− reacts with the protein moiety with rate constants of (5.1±0.6)×107M−1s−1 (pH 8.4, I∼0.27M) and (1.0±0.2)×108M−1s−1 (pH 10, I=0.5M). The absorption spectrum of the haem moiety was not changed, thus, amino acid radicals produced on the protein do not reduce the haem. The pH-dependent difference in rate constants may be attributed to differences in ionization states of amino acids and to the change in the conformation of the protein. With iron(II) cytochrome c, CO 3 •− oxidizes the haem quantitatively, presumably via electrostatic guidance of the radical to the solvent-accessible haem edge, with a different pH dependence: at pH 8.4, the rate constant is (1.1±0.1)×109M−1s−1 and, at pH 10, (7.6±0.6)×108M−1s−1. We propose that CO 3 •− oxidizes the iron center directly, and that the lower rate observed at pH 10 is due to the different charge distribution of iron(II) cytochrome c