title: The proton-pumping NADH:ubiquinone oxidoreductase (complex I) of Aquifex aeolicus.
abstract: The proton-pumping NADH:ubiquinone oxidoreductase, also called complex I, is the first energy-transducing complex of many respiratory chains. Homologues of complex I are present in the three domains of life. Here, we report the properties of complex I in membranes of the hyperthermophilic bacterium Aquifex aeolicus. The complex reacted with NADH but not with NADPH and F(420)H(2) as electron donors. Short-chain analogues of ubiquinone like decyl-ubiquinone and ubiquinone-2 were suitable electron acceptors. The affinities towards NADH and ubiquinone-2 were comparable to the ones obtained with the Escherichia coli complex I. The reaction was inhibited by piericidin A at the same concentration as in E. coli. The complex showed an unusual pH optimum at pH 9 and a maximal rate at 80 degrees C. We found no evidence for the presence of an alternative, single subunit NADH dehydrogenase in A. aeolicus membranes. The NADH:ferricyanide reductase activity of detergent extracts of A. aeolicus membranes sedimented as a protein with a molecular mass of approximately 550 kDa. From the data we concluded that A. aeolicus contains a NADH:ubiquinone oxidoreductase resembling complex I of mesophilic bacteria.
authors.affiliation: Heinrich-Heine-Universität Düsseldorf, Institut für Biochemie, Universitätsstr. 1, D-40225, Düsseldorf, Germany.
authors.forename: Dierk
authors.initials: D
authors.lastname: Scheide
authors.forename: Robert
authors.initials: R
authors.lastname: Huber
authors.forename: Thorsten
authors.initials: T
authors.lastname: Friedrich
mesh_terms: D000595:Amino Acid Sequence; D001419:Bacteria / Q000201:enzymology*; D042967:Electron Transport Complex I; D004734:Energy Metabolism; D006358:Hot Temperature; D008565:Membrane Proteins / Q000235:genetics / Q000378:metabolism; D008969:Molecular Sequence Data; D008970:Molecular Weight; D009247:NADH, NADPH Oxidoreductases / Q000235:genetics / Q000378:metabolism*; D017494:Proton Pumps / Q000235:genetics / Q000378:metabolism*; D017386:Sequence Homology, Amino Acid
chemical_list: D008565:Membrane Proteins; D017494:Proton Pumps; D009247:NADH, NADPH Oxidoreductases; C014227:ferricyanide reductase; D042967:Electron Transport Complex I