Superoxide Radical: An Endogenous Toxicant

The Two Faces of Oxygen Molecular oxygen is both benign and malign. On the one hand it provides enormous advantages and on the other it imposes a universal toxicity. This toxicity is largely due to the intermediates of oxygen reduction, i.e. 0;, H202, and OH·, and any organism that avails itself of the benefits of oxygen does so at the cost of maintaining an elaborate system of defenses against these intermediates. We will here concern ourselves with the superoxide dismutases which, by catalytically scavenging 0;, provide a defense against it and against any reactive radical species which can be derived from it.