Inactivation of the Na⁺‐translocating NADH:ubiquinone oxidoreductase from Vibrio alginolyticus by reactive oxygen species

The Na+‐translocating NADH:quinone oxidoreductase (Na+‐NQR) from Vibrio alginolyticus was inactivated by reactive oxygen species. Highest Na+‐NQR activity was observed in anaerobically prepared membranes that exhibited 1 : 1 coupling of NADH oxidation and Q reduction activities (1.6 U·mg−1). Optical and EPR spectroscopy documented the presence of b‐type cytochromes, a [2Fe−2S] cluster and an organic radical signal in anaerobically prepared membranes from V. alginolyticus. It is shown that the [2Fe−2S] cluster previously assigned to the Na+‐NQR originates from the succinate dehydrogenase or the related enzyme fumarate reductase