Occurrence of a reduced nicotinamide adenine dinucleotide oxidase activity linked to a cytochrome system in renal brush border membranes

NADH oxidase activity has been detected in luminal membrane derived from the proximal tubules of rat kidney (brush border membranes). The cytochromes associated with these membranes [García, M.L., Benavides, J., Valdivieso, F., Mayor, F., & Giménez-Gallego, G. (1978) Biochem. Biophys. Res. Commun. 82, 738-744] were reduced by NADH, the extent of this reduction being affected by the presence of oxygen and by inhibitors of this NADH oxidase activity. These results suggest that the cytochromes act as an electron transport system between NADH and oxygen. The possibility of mitochondrial contamination is excluded on the basis of differential sensitivity to inhibitors and marker enzyme activities.