Mössbauer spectroscopy on respiratory complex I: the iron-sulfur cluster ensemble in the NADH-reduced enzyme is partially oxidized.

TitleMössbauer spectroscopy on respiratory complex I: the iron-sulfur cluster ensemble in the NADH-reduced enzyme is partially oxidized.
Publication TypeJournal Article
Year of Publication2012
AuthorsBridges, HR, Bill, E, Hirst, J
Date Published2012 Jan 10
KeywordsCatalytic Domain, Electron Spin Resonance Spectroscopy, Electron Transport, Electron Transport Complex I, Ferric Compounds, Ferrous Compounds, Fungal Proteins, Iron-Sulfur Proteins, Mitochondrial Proteins, Oxidation-Reduction, Quinone Reductases, Spectroscopy, Mossbauer, Yarrowia

In mitochondria, complex I (NADH:quinone oxidoreductase) couples electron transfer to proton translocation across an energy-transducing membrane. It contains a flavin mononucleotide to oxidize NADH, and an unusually long series of iron-sulfur (FeS) clusters that transfer the electrons to quinone. Understanding electron transfer in complex I requires spectroscopic and structural data to be combined to reveal the properties of individual clusters and of the ensemble. EPR studies on complex I from Bos taurus have established that five clusters (positions 1, 2, 3, 5, and 7 along the seven-cluster chain extending from the flavin) are (at least partially) reduced by NADH. The other three clusters, positions 4 and 6 plus a cluster on the other side of the flavin, are not observed in EPR spectra from the NADH-reduced enzyme: they may remain oxidized, have unusual or coupled spin states, or their EPR signals may be too fast relaxing. Here, we use Mössbauer spectroscopy on (57)Fe-labeled complex I from the mitochondria of Yarrowia lipolytica to show that the cluster ensemble is only partially reduced in the NADH-reduced enzyme. The three EPR-silent clusters are oxidized, and only the terminal 4Fe cluster (position 7) is fully reduced. Together with the EPR analyses, our results reveal an alternating profile of higher and lower potential clusters between the two active sites in complex I; they are not consistent with the consensus picture of a set of isopotential clusters. The implications for intramolecular electron transfer along the extended chain of cofactors in complex I are discussed.

Alternate JournalBiochemistry
Citation Key10.1021/bi201644x
PubMed ID22122402
PubMed Central IDPMC3254188
Grant ListMC_U105663141 / / Medical Research Council / United Kingdom