A novel superoxide radical generator in heart mitochondria

Abstract

Experimental evidence is presented demonstrating the existence of a potent O2^.− ₂ source in heart mitochondria. The novel O^.− ₂ generator is more active than any other known mitochondrial O^.− ₂ generator and also exhibits a higher affinity for molecular oxygen. In contrast to mitochondrial O_{.− 2} sources reported previously [(1974) FEBS Lett. 42, 68–72; (1978) Eur. J. Biochem. 82, 563–567], the O^.− ₂ generator described in this paper is not involved in energy‐linked respiration. Superoxide radicals from this source require NADH to initiate their generation, and the radicals formed are released entirely into the extramitochondrial space. NADH‐related O^.− ₂ generation was also observed with the solubilized erogenous NADH oxidoreductase of heart mitochondria, an enzyme recently described [(1987) Eur. J. Biochem., submitted]. This finding together with the lack of an NADH‐dependent O^.− ₂ source in liver mithochondria suggests that the novel O^.− ₂ generator and the erogenous NADH oxidoreductase of heart mitochondria are identical.