Protective effect of NADP-isocitrate dehydrogenase on the paraquat-mediated oxidative inactivation of aconitase in heart mitochondria

Protective role of NADP-isocitrate dehydrogenase in the oxidative inactivation of mitochondrial enzymes was analyzed. Administration of paraquat to the rat inactivated liver mitochondrial enzymes: the aconitase activity decreased to one quarter, and citrate synthase and fumarase to half, whereas cytosolic enzymes were not affected. Activities of heart mitochondrial and cytosolic enzymes were not at all changed in the rat treated with paraquat, but paraquat directly inactivated aconitase in the heart mitochondria isolated from the non-treated rats. The paraquat-dependent inactivation of aconitase was prevented by activating NADP-isocitrate dehydrogenase in the presence of oxidized glutathione. NADP-isocitrate dehydrogenase could regenerate glutathione in isolated heart mitochondria, indicating that paraquat-mediated inactivation depends on the glutathione-regenerating activity by enhanced NADPH supply. Lower NADP-isocitrate dehydrogenase activity in liver mitochondria cannot regenerate reduced glutathione for scavenging reactive oxygen species, resulting in the paraquat-induced oxidative inactivation of mitochondrial enzymes. However, higher activity of NADP-isocitrate dehydrogenase participates in the regeneration of reduced glutathione causing stabilization of enzymes in heart mitochondria.