Production of reactive oxygen species by complex I (NADH:ubiquinone oxidoreductase) from Escherichia coli and comparison to the enzyme from mitochondria.

TitleProduction of reactive oxygen species by complex I (NADH:ubiquinone oxidoreductase) from Escherichia coli and comparison to the enzyme from mitochondria.
Publication TypeJournal Article
Year of Publication2008
AuthorsEsterházy, D, King, MS, Yakovlev, G, Hirst, J
JournalBiochemistry
Volume47
Issue12
Pagination3964-71
Date Published2008 Mar 25
ISSN0006-2960
KeywordsAnimals, Cattle, Electron Transport Complex I, Escherichia coli, Hydrogen Peroxide, Mitochondria, Heart, Oxidation-Reduction, Oxygen, Reactive Oxygen Species, Superoxides
Abstract

The generation of reactive oxygen species by mitochondrial complex I (NADH:ubiquinone oxidoreductase) is considered a significant cause of cellular oxidative stress, linked to neuromuscular diseases and aging. Defining its mechanism is important for the formulation of causative connections between complex I defects and pathological effects. Oxygen is probably reduced at two sites in complex I, one associated with NADH oxidation in the mitochondrial matrix and the other associated with ubiquinone reduction in the membrane. Here, we study complex I from Escherichia coli, exploiting similarities and differences in the bacterial and mitochondrial enzymes to extend our knowledge of O2 reduction at the active site for NADH oxidation. E. coli and bovine complex I reduce O2 at essentially the same rate, with the same potential dependence (set by the NAD (+)/NADH ratio), showing that the rate-determining step is conserved. The potential dependent rate of H2O2 production does not correlate to the potential of the distal [2Fe-2S] cluster N1a in E. coli complex I, excluding it as the point of O2 reduction. Therefore, our results confirm previous proposals that O2 reacts with the fully reduced flavin mononucleotide. Assays for superoxide production by E. coli complex I were prone to artifacts, but dihydroethidium reduction showed that, upon reducing O2, it produces approximately 20% superoxide and 80% H2O2. In contrast, bovine complex I produces 95% superoxide. The results are consistent with (but do not prove) a specific role for cluster N1a in determining the outcome of O2 reduction; possible reaction mechanisms are discussed.

DOI10.1021/bi702243b
Alternate JournalBiochemistry
Citation Key10.1021/bi702243b
PubMed ID18307315
Grant ListMC_U105663141 / / Medical Research Council / United Kingdom