THE NA-TRANSLOCATING NADH-UBIQUINONE OXIDOREDUCTASE FROM THE MARINE BACTERIUM VIBRIO-ALGINOLYTICUS CONTAINS FAD BUT NOT FMN()

The Na+-translocating NADH:ubiquinone oxidoreductase from Vibrio algin olyticus was extracted from the bacterial membranes and purified by io n exchange chromatographic procedures. The enzyme catalyzed NADH oxida tion by suitable electron acceptors, e.g. menadione, and the Na+ and N ADH-dependent reduction of ubiquinone-1. Four dominant bands and a num ber of minor bands were visible on SDS-PAGE that could be part of the enzyme complex. Flavin analyses indicated the presence of FAD but no F MN in the purified enzyme. FAD but no FMN: were also present in V. alg inolyticus membranes. FAD is therefore a prosthetic group of the Na+-t ranslocating NADH:ubiquinone oxidoreductase and FMN is not present in the enzyme. The FAD was copurified with the NADH dehydrogenase. The pu rified enzyme exhibited an absorption spectrum with a maximum at 450 n m that is typical for a flavoprotein. Upon incubation with NADH this a bsorption disappeared indicating reduction of the enzyme-bound FAD.