Characterization of a hexammineruthenium-stimulated external NADH oxidase from rat liver mitochondria.

The existence of an external hexammineruthenium-stimulated NADH oxidase in rat liver mitochondria is postulated. This enzyme is localized on the outer surface of the inner mitochondrial membrane, is specific for NADH and requires oxygen. The apparent affinity of the enzyme for NADH amounts to about 4 microM. Furthermore, the enzyme is characterized by an alkaline pH optimum and a linear Arrhenius plot (14 kJ/mol). The electron transfer from NADH to oxygen is not linked with the respiratory chain but is connected with the formation of superoxide radicals.