Reactions of peroxynitrite in the mitochondrial matrix

Superoxide radical (O-2(-)) and nitric oxide (NO) produced at the mitochond rial inner membrane react to form peroxynitrite (ONOO-) in the mitochondria l matrix. Intramitochondrial ONOO- effectively reacts with a few biomolecul es according to reaction constants and intramitochondrial concentrations. T he second-order reaction constants tin M-1 s(-1)) of ONOO- with NADH (233 /- 27), ubiquinol-0 (485 +/- 54) and GSH (183 +/- 12) were determined fluor ometrically by a simple competition assay of product formation. The oxidati on of the components of the mitochondrial matrix by ONOO- was also followed in the presence of CO2, to assess the reactivity of the nitrosoperoxocarbo xylate adduct (ONOOCO2-) towards the same reductants. The ratio of product formation was about similar both in the presence of 2.5 mM CO2 and in air-e quilibrated conditions. Liver submitochondrial particles supplemented with 0.25-2 mu M ONOO- showed a O-2(-) production that indicated ubisemiquinone formation and autooxidation. The nitration of mitochondrial proteins produc ed after addition of 200 mu M ONOO- was observed by Western blot analysis. Protein nitration was prevented by the addition of 50-200 mu M ubiquinol-0 or GSH. An intramitochondrial steady state concentration of about 2 nM ONOO - was calculated, taking into account the rate constants and concentrations of ONOO- coreactants. (C) 2000 Elsevier Science Inc.