[10] Superoxide dismutase assays

The primary difficulty in assaying Superoxide dismutase (SOD) for its enzymatic activity consists in the free radical nature of its substrate O2·- which can only be supplied by generation within the assay medium. The substrate O2·- cannot easily be detected directly by conventional analytical tools. Routine testing of SOD, therefore, is performed according to a general principle, which is explained in the chapter. If an absolute measure of physiological levels of SOD is intended, a direct immunochemical method is suggested in addition to activity measurements. This chapter focuses on measuring SOD in biological media. It presents a qualitative test for SOD activity based on the reduction of nitro blue tetrazolium (NBT) by O2·-, a simple immunological determination of the SOD molecule of sufficient sensitivity and avoiding labeled reagents, and an indirect measure of SOD activity to be used in purified samples.