Sites and mechanisms responsible for the low rate of free radical production of heart mitochondria in the long-lived pigeon

Abstract

Basal (substrate alone) and maximum rates of H 2O 2 production, oxygen consumption and free radical leak in the respiratory chain were higher in heart mitochondria of the short-lived rat (4 years) than in the long-lived pigeon (35 years). This suggests that the low free radical production of pigeon heart mitochondria is due in part to both a low electron flow and a low percent leak of electrons out of sequence in the respiratory chain. Thenoyltrifluoroacetone did not increase H 2O 2 production with succinate either in rats or pigeons. Mitochondrial H 2O 2 production was higher with pyruvate/malate than with succinate in both animal species. Rotenone and antimycin A increased H 2O 2 production with pyruvate/malate to the maximum levels observed in each species. Addition of myxothiazol to antimycin A-treated mitochondria supplemented with pyruvate/malate decreased H 2O 2 production in both species. All the combinations of inhibitors added with pyruvate/malate resulted in higher rates of H 2O 2 production in rats than in pigeons. When succinate instead of pyruvate/malate was used as substrate, rotenone and thenoyltrifluoroacetone decreased mitochondrial H 2O 2 production in the rat and did not change it in the pigeon. The results indicate that Complexes I and III are the main H 2O 2 generators of heart mitochondria in rats and pigeons and that both Complexes are responsible for the low H 2O 2 production of the bird. p-Chloromercuribenzoate and ethoxyformic anhydride strongly inhibited the H 2O 2 production induced by rotenone with pyruvate/malate in both species. This suggests that the free radical generator of Complex I is located after the ferricyanide reduction site, between the ethoxyformic and the rotenone-sensitive sites.