Superoxide radicals and hydrogen peroxide formation in mitochondria from normal and neoplastic tissues

Mitochondria from beef heart, Morris hepatoma 3924A and Ehrlich ascites tumor (Lettré mutant) have been studied with respect to hydrogen peroxidase and superoxide radical formation and the presence of superoxide dismutase activity (EC 1.15.1.1, superoxide:superoxide oxidoreductase). The generation of superoxide radicals and hydrogen peroxide occurs at the level of the membrane, being present also in mitochondrial fragments. Hepatoma and ascites mitochondria have little or no superoxide dismutase activity. Superoxide radicals appear to be precursors of hydrogen peroxide formation, the reaction being catalyzed by superoxide dismutase.