Does more MnSOD mean more hydrogen peroxide?

Superoxide dismutases (SODs) are a family of important antioxidant enzymes that catalyze the conversion of superoxide to hydrogen peroxide and oxygen. Hydrogen peroxide is then detoxified by a host of antioxidant enzymes. A common misconception is that the increased MnSOD levels will result in increased hydrogen peroxide levels. Herein we offer some potential reasons for this confusion, as well as some potential resolutions. Data are offered that demonstrate the ability of MnSOD, in the presence of nitric oxide, to utilize hydrogen peroxide to produce superoxide and the more toxic oxidant, peroxynitrite.