Redox properties of the [2Fe-2S] center in the 24 kDa (NQO2) subunit of NADH:ubiquinone oxidoreductase (complex I).

TitleRedox properties of the [2Fe-2S] center in the 24 kDa (NQO2) subunit of NADH:ubiquinone oxidoreductase (complex I).
Publication TypeJournal Article
Year of Publication2002
AuthorsZu, Y, Di Bernardo, S, Yagi, T, Hirst, J
JournalBiochemistry
Volume41
Issue31
Pagination10056-69
Date Published2002 Aug 06
ISSN0006-2960
KeywordsAmino Acid Sequence, Animals, Base Sequence, Cattle, Electrochemistry, Electron Transport Complex I, Escherichia coli, Histidine, Hydrogen-Ion Concentration, Mitochondria, Heart, Molecular Sequence Data, Mutagenesis, Site-Directed, NADH, NADPH Oxidoreductases, Osmolar Concentration, Sequence Homology, Amino Acid
Abstract

The redox properties of the [2Fe-2S] cluster in the 24 kDa subunit of bovine heart mitochondrial NADH:ubiquinone oxidoreductase (complex I) and three of its homologues have been defined using protein-film voltammetry. The clusters in all four examples display characteristic, pH-dependent redox transitions, which, unusually, can be masked by high ionic strength conditions. At low ionic strength (10 mM NaCl) the reduction potential varies by approximately 100 mV between high and low pH limits (pH 5 and 9); thus the redox process is not strongly coupled and is unlikely to form part of the mechanism of energy transduction in complex I. The pH dependence was shown to result from pH-linked changes in protein charge, due to nonspecific protonation events, rather than from the coupling of a specific ionizable residue, and the ionic strength dependence at high and low pH was modeled using extended Debye-Hückel theory. The low potential of the 24 kDa subunit [2Fe-2S] cluster, out of line with the potentials of the other iron-sulfur clusters in complex I, is suggested to play a role in coupling reducing equivalents at the catalytic active site. Finally, the validity of using the [2Fe-2S] cluster in an isolated subunit, as a mechanistic basis for coupled proton-electron transfer in intact complex I, is evaluated.

DOI10.1021/bi026026f
Alternate JournalBiochemistry
Citation Key10.1021/bi026026f
PubMed ID12146970
Grant ListM01 RR 00833 / RR / NCRR NIH HHS / United States
R01 GM 33712 / GM / NIGMS NIH HHS / United States