Nitric oxide inhibits electron transfer and increases superoxide radical production in rat heart mitochondria and submitochondrial particles

Nitric oxide ((NO)-N-.) released by S-nitrosoglutathione (GSNO) inhibited enzymatic activities of rat heart mitochondrial membranes. Cytochrome oxidase activity was inhibited to one-half at an effective (NO)-N-. concentration of 0.1 mu M, while succinate- and NADH-cytochrome-c reductase activities were half-maximally inhibited at 0.3 mu M (NO)-N-.. Submitochondrial particles treated with (NO)-N-. (either from GSNO or from a pure solution) showed increased O-2(-) and H2O2 production when supplemented with succinate alone, at rates that were comparable to those of control particles with added succinate and antimycin. Rat heart mitochondria treated with (NO)-N-. also showed increased H2O2 production. Cytochrome spectra and decreased enzymatic activities in the presence of (NO)-N-. are consistent with a multiple inhibition of mitochondrial electron transfer at cytochrome oxidase and at the ubiquinone-cytochrome b region of the respiratory chain, the latter leading to the increased O-2(-) production, Electrochemical detection showed that the buildup of a (NO)-N-. concentration from GSNO was interrupted by submitochondrial particles supplemented with succinate and antimycin and was restored by addition of superoxide dismutase. The inhibitory effect of (NO)-N-. on cytochrome oxidase was also prevented under the same conditions. Apparently, mitochondrial O-2(-) reacts with (NO)-N-. to form peroxynitrite and, by removing NO, reactivates the previously inhibited cytochrome oxidase, It is suggested that, at physiological concentrations of (NO)-N-., inhibition of electron transfer, (NO)-N-.-induced O-2(-) pro duction, and ONOO- formation participate in the regulatory control of mitochondrial oxygen uptake. (C) 1996 Academic Press, Inc.