NAD(P)H- and superoxide-dependent nitric oxide degradation by rat liver mitochondria

Mitochondria consume nitric oxide (NO) mainly through reaction with superoxide anion (O2-). Here, we analyzed the O2- sources for NO degradation by isolated rat liver mitochondria. Electron leakage from complex III and reverse electron transport to complex I accounted for O2--dependent NO degradation by mitochondria in the presence of a protonmotive force. Mitochondria incubated with NAD(P)H also presented intense O2- generation and NO degradation rates that were insensitive to respiratory inhibitors and abolished after proteinase treatment. These results suggest that an outer membrane-localized NAD(P)H oxidase activity, in addition to the electron leakage from the respiratory chain, promotes O2--dependent NO degradation in rat liver mitochondria.