High protonic potential actuates a mechanism of production of reactive oxygen species in mitochondria

Abstract

Formation of H 2O 2 has been studied in rat heart mitochondria, pretreated with H 2O 2 and aminotriazole to lower their antioxidant capacity. It is shown that the rate of H 2O 2 formation by mitochondria oxidizing 6 mM succinate is inhibited by a protonophorous uncoupler, ADP and phosphate, malonate, rotenone and myxothiazol, and is stimulated by antimycin A. The effect of ADP is abolished by carboxyatractylate and oligomycin. Addition of uncoupler after rotenone induces further inhibition of H 2O 2 production. Inhibition of H 2O 2 formation by uncoupler, malonate and ADP+P i is shown to be proportional to the ΔΨ decrease by these compounds. A threshold ΔΨ value is found, above which a very strong increase in H 2O 2 production takes place. This threshold slightly exceeds the state 3 ΔΨ level. The data obtained are in line with the concept [Skulachev, V.P., Q. Rev. Biophys. 29 (1996), 169–202] that a high proton motive force in state 4 is potentially dangerous for the cell due to an increase in the probability of superoxide formation.