Succinate is the controller of O2−/H2O2 release at mitochondrial complex I : negative modulation by malate, positive by cyanide

Mitochondrial production of H 2 O 2 is low with NAD substrates (glutamate/pyruvate, 3 and 2 mM) (G/P) and increases over ten times upon further addition of succinate, with the formation of a sigmoidal curve (semimaximal value at 290 µM, maximal H 2 O 2 production at 600 µM succinate). Malate counteracts rapidly the succinate induced increased H 2 O 2 release and moves the succinate dependent H 2 O 2 production curve to the right. Nitric oxide (NO) and carbon monoxide (CO) are cytochrome c oxidase inhibitors which increase mitochondrial ROS production. Cyanide (CN − ) was used to mimic NO and CO. In the presence of G/P and succinate (300 µM), CN − progressively increased the H 2 O 2 release rate, starting at 1.5 µM. The succinate dependent H 2 O 2 production curve was moved to the left by 30 µM CN − . The V max was little modified. We conclude that succinate is the controller of mitochondrial H 2 O 2 production, modulated by malate and CN − . We propose that succinate promotes an interaction between Complex II and Complex I, which activates O 2 − production.