The proton-pumping NADH:ubiquinone oxidoreductase (complex 1) of Aquifex aeolicus

The proton-pumping NADH:ubiquinone oxidoreductase, also called complex 1, 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 F420H2 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 80degreesC. 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 Ne concluded that A. acolicus contains a NADH: ubiquinone oxidoreductase resembling complex I of mesophilic bacteria. (C) 2002 Federation of European Microbiological Societies. Published by Elsevier Science B.V. All rights reserved.