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) inhibi ted enzymatic activities of rat heart mitochondrial membranes. Cytochr ome oxidase activity was inhibited to one-half at an effective (NO)-N- . concentration of 0.1 mu M, while succinate- and NADH-cytochrome-c re ductase 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 whe n supplemented with succinate alone, at rates that were comparable to those of control particles with added succinate and antimycin. Rat hea rt mitochondria treated with (NO)-N-. also showed increased H2O2 produ ction. Cytochrome spectra and decreased enzymatic activities in the pr esence of (NO)-N-. are consistent with a multiple inhibition of mitoch ondrial electron transfer at cytochrome oxidase and at the ubiquinone- cytochrome b region of the respiratory chain, the latter leading to th e increased O-2(-) production, Electrochemical detection showed that t he buildup of a (NO)-N-. concentration from GSNO was interrupted by su bmitochondrial particles supplemented with succinate and antimycin and was restored by addition of superoxide dismutase. The inhibitory effe ct 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 inh ibited cytochrome oxidase, It is suggested that, at physiological conc entrations of (NO)-N-., inhibition of electron transfer, (NO)-N-.-indu ced O-2(-) pro duction, and ONOO- formation participate in the regulat ory control of mitochondrial oxygen uptake. (C) 1996 Academic Press, I nc.