Inactivation of mitochondrial adenosine triphosphatase from Trypanosoma cruzi by oxygen radicals.

Incubation of Trypanosoma cruzi mitochondrial ATPase (Fo-F1) with the xanthine oxidase system (XO), Fenton's reagent (Fe2+ + H2O2) and the ascorbate-Cu system, caused gradual loss of enzyme activity, which increased as a function of incubation time and rate of oxygen radical generation. The essential role of OH. radicals for ATPase inactivation was supported by a) the enzyme protection afforded by superoxide dismutase, catalase and mannitol, when using the XO system; b) the similar effect of mannitol and benzoate with Fenton's reagent; c) the similar effect of catalase, EDTA and histidine with the ascorbate-Cu system; d) the increased rate of ATPase inactivation by 1) the XO system supplemented with chelated iron, and 2) the ascorbate-Cu system supplemented with H2O2. Comparison of oxygen radical generators for their action on membrane-bound (Fo-F1) and soluble F1 revealed that ascorbate-Cu was the most effective one, possibly because of its capability of producing OH. radicals that react preferentially with the enzyme at their formation site.