Superoxide Dismutase Inhibition of Oxidation of Ubiquinol and Concomitant Formation of Hydrogen Peroxide

Abstract

We measured ubiquinone (CoQ₀) and hydrogen peroxide (H₂O₂) formed in the process of oxidation of ubiquinol (CoQ₀H₂). We found that copper-zinc superoxide dismutase and manganese superoxide dismutase inhibited both the CoQ₀ formation and the H₂O₂ formation only in the presence of chelators such as DTPA (diethylenetriaminepentaacetic acid). The amount of H₂O₂ was almost equal to that of CoQ₀, indicating that the H₂O₂ formation was coupled with the CoQ₀ formation. The lack of inhibitory effects of the corresponding heat-inactivated superoxide dismutase (SOD) confirmed that the inhibition by the original SOD was due to its enzymatic activity. We propose that CoQ₀H₂ oxidation occurs as a chain reaction with superoxide as the chain carrier and that SOD inhibits this reaction by lowering the superoxide concentration.