Catalysis of the disproportionation of superoxide by metalloporphyrins. III.

An assay based on the use of an oxygen electrode has been used to determine the superoxide dismutase-type activity of several metalloporphyrins. Both the iron(III) and manganese(III) derivatives of tetrakis-(4-N-methylpyridyl)porphine were shown to have comparable activity, about 2-3% of that of the enzyme. Comparisons are made between this assay method and the more standard one which depends on the conversion of nitroblue tetrazolium to formazan.