Redox cycling of polycyclic aromatic hydrocarbon o-quinones: metal ion-catalyzed oxidation of catechols bypasses inhibition by superoxide dismutase

Several two-electron quinone reductases catalyze the redox cycling of polycyclic aromatic hydrocarbon (PAH) o-quinones. When the carbonyl reductase of human placenta catalyzes the cycling of 9,10-phenanthrenequinone in aqueous phosphate buffer, reactive oxygen species are produced. Superoxide dismutase (SOD) inhibits the cycling by more than 90%, but the addition of 1 μM Cu2+ or 15 μM ferricytochrome c (cyt c3+) completely restores the cycling...