Inactivation of the mitochondrial adenosine triphosphatase from Trypanosoma cruzi by oxygen radicals: role of thiol groups.

: Inactivation of Trypanosoma cruzi mitochondrial ATPase by oxygen radicals, generated by redox cycling of the ascorbate-Cu system (Cataldi de Flombaum, M.A. and Stoppani, A.O.M. (1986) Biochem. Int. 12, 785-793), involves oxidation of the enzyme thiols, as indicated by the competitive kinetics obtained with p-chloromercuribenzoate, a selective SH-reagent. Dithiothreitol prevented the ascorbate-Cu effect but did not reactivate the enzyme. Non-competitive kinetics were obtained with ascorbate-Cu and increasing MgATP concentration, or with phenylglyoxal, as second inhibitor. Since phenylglyoxal reacts with arginyl residues at the ATPase hydrolytic site, these results suggest that the oxgen-sensitive thiols were located outside the hydrolytic site.