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 microM, maximal H(2)O(2) production at 600 microM 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 microM), CN(-) progressively increased the H(2)O(2) release rate, starting at 1.5 microM. The succinate dependent H(2)O(2) production curve was moved to the left by 30 microM 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.