Effects of metals, ligands and antioxidants on the reaction of oxygen with 1,2,4-benzenetriol

1,2,4-Benzenetriol is an active metabolite of the human leukemogen benzene that reacts rapidly with molecular oxygen (O2). The mechanism of autoxidation of benzenetriol is scantily characterized, and little is known of the effects of metals, metal chelators, radical scavengers, and antioxidants on the rate of reduction of O2. Here, we report that catalytic amounts of Cu2+ and Fe3+ accelerated the oxidation of benzenetriol (250 μM) in a dose-dependent manner. Fe3+ (50 μM) increased the rate of autoxidation by 91%, and Cu2+ (10 μM) increased it 11-fold. In the absence of added metals, superoxide dismutase inhibited and desferrioxamine stimulated the autoxidation. In the Cu2+-catalyzed reaction, superoxide dismutase neither inhibited nor stimulated, while desferrioxamine abolished the catalysis by Cu2+. In the presence of Fe3+, superoxide dismutase slowed the reaction, but desferrioxamine, surprisingly, did not. The presence of both superoxide dismutase and desferrioxamine blocked the autoxidation, either in the presence or absence of metals. We conclude: (1) superoxide is a propagator of sequential one-electron transfer reactions in the absence of added metals; (2) addition of Cu2+, unlike Fe3+, removes the dependence of the reaction on propagation by superoxide, presumably changing the radical-propagated chain reaction to a concerted two-electron transfer; (3) the further addition of desferrioxamine restores superoxide-dependent propagation. Taken with our previous data on the genotoxicity of benzenetriol, These findings have implications regarding a role for transition metals in the carcinogenicity of benzene.