Haemoglobin oxidation and free radical production in the red cell

The production and fate of superoxide and other free radicals, and the role of superoxide dismutase in the red cell is considered. Superoxide reacts slowly and at a comparable rate with oxyhaemoglobin and methaemoglobin, but superoxide dismutase markedly accelerates oxidation of oxyhaemoglobin by oxidizing drugs or xenobiotics such as quinones or paraquat. The mechanism involves inhibition by the enzyme (via its reaction with superoxide) of methaemoglobin reduction by the drug radicals. The possibility that such inhibition of organic radical reactions by superoxide dismutase is one of its protective functions is discussed.