Ubiquinol-centered nitric oxide oxidative reaction in mitochondria

SCHÖPFER F; LISDERO C; CARRERAS MC; RIOBÓ N; CADENAS E; PODEROSO JJ

Santa Bárbara, EEUU

Congreso; World Congress “Oxidant and antioxidants in Biology”; 1999

Oxygen Club of California

We have previously reported that nitric oxide (NO) increases the superoxide anion (O2-) and hydrogen peroxide (H2O2) production by reacting with ubiquinol. The sequence of reactions are: [1] NO + QH2 ® Q- + NO-, [2 ] Q- + O2 ® O2- + Q, [3] O2- + O2- ® H2O2 + O2, and [4] NO + O2- ® ONOO- (peroxynitrite). The aim of this study was to relate NO decay (-d[NO]/dt), H2O2 production (d[H2O2]/dt) and ONOO- formation to ubiquinol concentration in liver mitochondria and submitochondrial particles (SMP). Mitochondria were exposed to a single pulse of NO (0.2-2 µM) and the membrane potential, -d[NO]/dt and oxygen uptake were recorded. Addition of Q-0H2 increased by 20% the -d[NO]/dt while 2 µM SOD decreased by 30% the -d[NO]/dt. supplementation with Q-0 and Q-2 reduced to QH2 in SMP with 6 mM succinate and 6 mM myxothiazol increased d[H2O2]/dt and decreased by 3 fold the cytochrome oxidase inhibition time, the latter effect was reverted by SOD. In addition, d[H2O2]/dt was dose-dependently increased by NO up to 3 µM concentration while its detection decreased at higher NO concentrations. The  relation between d[H2O2]/dt and the QH2 concentrations indicate that a cohort of oxidative reactions (1-4) take place in mitochondria including the formation of ONOO-. We also observed that ONOO- oxidizes ubiquinol according to reaction [5] ONOO- + QH2 ® .NO2 + Q-. In addition, SMP supplemented with 0.25-2 µM ONOO-, released 0.015-0.1 µM min-1 O2- in order to reactions [5] and [2]. It is likely that, at least a part of NO-induced O2- release, depends on ONOO- formed in mitochondria by reactions [1-3]. The mitochondrial ubiquinol-centered oxidative reactions could modulate NO concentration and its effects on mitochondria; moreover, the reversibility of NO effects should also depend on QH2 concentration in the mitochondrial membranes.