[Determination of the activity of superoxide dismutase in terms of rea substrate conversion]

On the basis of photochemical generation of O2.- and the tetrazolium/formazan system as indicating reaction an assay for SOD was developed which allows the determination of initial rate velocities of the enzyme. This was achieved by a special apparatus yielding the continuous registration of product formation simultaneously with the photochemical generation of O2.-. The investigation of the indicating reaction revealed that the reduction of nitro blue tetrazolium chloride to formazan is stoichiometrical with respect to riboflavin/methionine generated O2.- above pH 9. On this basis, an activity unit of SOD can be defined as real substrate consumption. One unit of the enzyme causes a decrease in the formation of formazan of 1 mumol/min under defined conditions.