Identification of an external NADH oxidase in rat kidney cortex mitochondria

Intact rat kidney cortex mitochondria oxidize external NADH and NADPH. Basal NADH oxidation of mitochondria, but not basal NADPH oxidation, is stimulated by hexammine-ruthenium (HR). 10.7 mumol/l HR induce 50% of the maximal NADH-oxidizing activity and amounted to 169 nmol NADH/min/mg of mitochondrial protein. The HR-stimulated NADH oxidation involves a stoichiometric 1:1 oxygen consumption. The electron transfer from NADH to oxygen does not occur via the respiratory chain complex I, but is connected with a superoxide anion radical formation. Experiments with intact mitochondria, submitochondrial particles and inner mitochondrial membranes show that rat kidney cortex mitochondria possess a NADH oxidase localized on the outer surface of the inner mitochondrial membrane.