Superoxide dismutases: anti- versus pro- oxidants?

The family of superoxide dismutases (SODs) are well known for their antioxidant actions exerted by catalyzing the conversion of O(2)(·-) into H(2)O(2) plus oxygen. The importance of this action is revealed by the multiple phenotypic deficits exhibited by a variety of organisms that have been made to lack one or more of the SODs. Never the less there have been reports of deleterious consequences caused by overproduction of SOD. Several explanations have been proposed for these counter intuitive effects; one of which is that elevated SOD causes increased formation of H(2)O(2). The reasons for dismissing this explanation are explored.