Manganese ions induce H2O2 generation at the ubiquinone binding site of mitochondrial complex II

Manganese-induced toxicity has been recently associated with an increased ROS generation from mitochondrial complex II (succinate:ubiquinone oxidoreductase). To achieve a deeper mechanistic understanding how divalent manganese ions (Mn2+) could stimulate mitochondrial ROS production we performed investigations with bovine heart submitochondrial particles (SMP). In succinate fueled SMP, the Mn2+ induced hydrogen peroxide (H2O2) production was blocked by the specific complex II ubiquinone binding site (IIQ) inhibitor atpenin A5 while a further downstream block at complex III increased the rate markedly. This suggests that site IIQ was the source of the reactive oxygen species. Moreover, Mn2+ ions also accelerated the rate of superoxide dismutation, explaining the general increase in the measured rates of H2O2 production and an attenuation of direct superoxide detection.