THIOLS PROTECT THE INHIBITION OF MYOCARDIAL ACONITASE BY PEROXYNITRITE

Peroxynitrite (ONOO-) is a potent inhibitor of myocardial aconitase. B ecause ONOO- reacts with sulfhydryl moieties, we investigated whether thiols protect against ONOO--mediated inhibition of aconitase. Aconita se activity was examined in ventricular homogenates prepared from fres hly isolated rat hearts. Peroxynitrite, but not the nitric oxide donor S-nitroso-N-acetyl-d,l-penicillamine (0.03-300 mu M), inhibited aconi tase activity (IC50 = 47 +/- 6 mu M). L-Cysteine (0.03-300 mu M), glut athione (0.03-3 mM), and N-(2-mercaptoproprionyl)-glycine (MPG, 0.03-3 mM) protected against the inhibitory effect of ONOO- (100 mu M) with the rank order of potency of MPG > glutathione > L-cysteine. D-Cystein e (3 mM) had a protective effect to L-cysteine, but L-cystine, the oxi dized form of L-cysteine, offered no protection. Ferrous ammonium sulf ate (1 mM) markedly enhanced the protection provided by L-cysteine, bu t not be glutathione of MPG. Thiols protect myocardial aconitase again st inhibition by ONOO- in a manner which is sulfhydryl group dependent and not stereospecific. The protection is related to the maintenance of the redox state of the iron-sulfur cubane cluster and cysteine resi dues at the active site of the enzyme. Both naturally occurring thiols and thiol-based drugs may be useful to protect the heart during ische mia-reperfusion injury where there is an excessive production of ONOO- . (C) 1998 Academic Press.