Nitric oxide inhibits mitochondrial NADH : ubiquinone reductase activity through peroxynitrite formation

This study was aimed at assessing the effects of long-term exposure to NO o f respiratory activities in mitochondria from different tissues (with diffe rent ubiquinol contents), under conditions that either promote or prevent t he formation of peroxynitrite. Mitochondria and submitochondrial particles isolated from rat heart, liver and brain were exposed either to a steady-st ate concentration or to a bolus addition of NO. NO induced the mitochondria l production of superoxide anions, hydrogen peroxide and peroxynitrite. the latter shown by nitration of mitochondrial proteins. Long-term incubation of mitochondrial membranes with NO resulted in a persistent inhibition of N ADH: cytochrome c reductase activity, interpreted as inhibition of NADH: ub iquinone reductase (Complex I) activity, whereas succinate:cytochrome c red uctase activity, including Complex II and Complex III electron transfer, re mained unaffected. This selective effect of NO and derived species was part ially prevented by superoxide dismutase and uric acid. In addition, peroxyn itrite mimicked the effect of NO, including tyrosine nitration of some Comp lex I proteins. These results seem to indicate that the inhibition of NADH: ubiquinone reductase (Complex I) activity depends on the NO-induced genera tion of superoxide radical and peroxynitrite and that Complex I is selectiv ely sensitive to peroxynitrite. Inhibition of Complex I activity by peroxyn itrite may have critical implications for energy supply in tissues such as the brain, whose mitochondrial function depends largely on the channelling of reducing equivalents through Complex I.