Metabolism of peroxynitrite in the mitochondrial matrix

VALDEZ LB; ZAOBORNYJ T; BOVERIS A

Buenos Aires, Argentina

Congreso; XIIth Meeting of the Society for Free Radical Research International; 2004

Society for Free Radical Research International

Nitric oxide (NO) and superoxide radical (O2-), produced at the mitochondrial inner membrane, react to form peroxynitrite (ONOO-) in the mitochondrial matrix. Nitric oxide production by mitochondrial nitric oxide synthase (mtNOS) shows rates of 0.5-1.4 nmol NO/min.mg protein and KM O2 in the 40-70 mM range, for liver, brain and kidney mitochondria. The rates of O2- production (0.5-13 nmol O2-/min.mg protein) depend on O2 concentration up to 1.1 mM. Intramitochondrial NO, O2- and ONOO- steady state concentrations were calculated for the physiological level of 20 mM O2, being 20-40 nM NO, 0.17-0.33 nM O2-, and 0.6-2.2 nM ONOO- for the three organs. Intramitochondrial ONOO- reacts effectively with the matrix reductants according to their reaction constants and intramitochondrial concentrations. The second-order constants  for  the  reaction of  ONOO- with NADH  (1.8 x 103 M-1s-1)  and  ubiquinol-0 (3.7 x 103 M-1s-1) were determined fluorometrically by a competition assay and taking into account the rate constants of ONOO- with GSH (1.4 x 103 M-1s-1). The oxidation of the components of the mitochondrial matrix by ONOO- was also followed in the presence of CO2, to assess the reactivity of the nitrosoperoxocarboxylate adduct (ONOOCO2-) towards the same reductants. Product formation was about similar both in the presence of 0.25 mM CO2 and in air-equilibrated conditions. Although in physiological O2 concentrations, ONOO- is effectively quenched by intramitochondrial reductants, in pathological conditions, ONOO- (5-30 nM), leads to protein nitration and mitochondrial dysfunction