Complex I (NADH-ubiquinone oxidoreductase) can form superoxide during forward electron
flow (NADH-oxidizing) or, at sufficiently high protonmotive force, during reverse electron
transport from the ubiquinone (Q) pool (NAD+-reducing). We designed an assay system to
allow titration of the redox state of the superoxide-generating site during reverse electron
transport in rat skeletal muscle mitochondria: a protonmotive force generated by ATP
hydrolysis, succinate: malonate to alter electron supply and modulate the redox state of the …