Superoxide dismutase: determination of activity by inhibition of photosensitized chemiluminescence of glycyltryptophan

A technique for quantitative determination of superoxide dismutase (SOD) in biological material is described. The technique is based on the riboflavin-photosensitized oxidation of Gly-Trp, which is accompanied by chemiluminescence. Formation of the luminescent product is inhibited by SOD. The dependence of SOD activity on reciprocal intensity of chemiluminescence is linear. The concentration for 50% inhibition is 7.5 ng/ml, and the minimum reliably determined concentration is about 2 ng/ml. The reaction is not sensitive to high concentrations of cyanide, which allows the separate determination of Cu,Zn- and Mn-SOD in mixtures.