Reduction of the iron-sulfur clusters in mitochondrial NADH:ubiquinone oxidoreductase (complex I) by EuII-DTPA, a very low potential reductant.

TitleReduction of the iron-sulfur clusters in mitochondrial NADH:ubiquinone oxidoreductase (complex I) by EuII-DTPA, a very low potential reductant.
Publication TypeJournal Article
Year of Publication2008
AuthorsReda, T, Barker, CD, Hirst, J
JournalBiochemistry
Volume47
Issue34
Pagination8885-93
Date Published2008 Aug 26
ISSN1520-4995
KeywordsAnimals, Cattle, Electron Spin Resonance Spectroscopy, Electron Transport Complex I, Iron, Iron-Sulfur Proteins, Mitochondria, Heart, Models, Biological, Oxidation-Reduction, Pentetic Acid, Protein Subunits, Sulfur
Abstract

NADH:ubiquinone oxidoreductase (complex I) is the first enzyme of the mitochondrial electron transport chain. It contains a flavin mononucleotide to oxidize NADH, and eight iron-sulfur clusters. Seven of them transfer electrons between the flavin and the quinone-binding site, and one is on the opposite side of the flavin. Although most information about their properties is from EPR, the spectra from only five clusters have been observed, and it is difficult to match them to the structurally defined clusters. Here, we analyze complex I from bovine mitochondria reacted with a very low potential reductant, to impose a potential approaching -1 V. We compare the spectra with those from higher potentials and from the 24 kDa subunit and flavoprotein subcomplex, and model the spectra by starting from those with fewer components and building the complexity gradually. Spectrum N1a, from the 24 kDa subunit [2Fe-2S] cluster, is not observed in bovine complex I at any potential. Spectrum N1b, from the 75 kDa subunit [2Fe-2S] cluster, exhibits a lower potential than the N3, N4 and N5 spectra of three [4Fe-4S] clusters. In the lowest potential spectra an N5-type spectrum is observed at unusually high temperature (indicating a significant change to the cluster, or that two clusters have very similar g values), the relaxation rate of N1b increases (indicating that a nearby cluster has become reduced) and a new feature with an apparent g value of 2.16 suggests an interaction between two reduced clusters. The consequences of these observations for electron transfer in complex I are discussed.

DOI10.1021/bi800437g
Alternate JournalBiochemistry
Citation Key10.1021/bi800437g
PubMed ID18651753
Grant ListMC_U105663141 / / Medical Research Council / United Kingdom