Superoxide Dismutase Activities of an Iron Porphyrin and other Iron Complexes

Abstract

The superoxide dismutase (SOD) activities of a number of metal complexes have been measured and a mathematical model is proposed which allows their rate constants to be calculated. Fc(CN)64- showed no activity whereas Fe(CN)63- appeared to react stoichiometrically with superoxide. True catalytic SOD activity appeared to be shown by chelates of iron withEDTA [Fe(EDTA)and Fe(EDTA)2], with diethylenetriaminepentaaceticacid [Fc(DTPA)2- and Fe(DTPA)3-]+and with o-phenanthroline (Fe(phen)32+). The most efficient superoxide dismutase catalyst of the compounds tested here was foundto be tetrakis(4-;Y-methylpyridyl)porphineiron(lll)]FeIIITMpyP], with a rate constant of 3 X 107M-l s-l at pH 10.1. Expo-sure of this compound to H2O2 produced in a superoxide-generating system caused its degradation to a product with lowerSOD activity, but it could be protected by catalasc. H2TMpyP itself showed no SOD activity, nor did its complexes with Zn(II)or Cu(II). CoIIITMpyP showed much lower SOD activity than the Fc(III) complex.© 1979, American Chemical Society. All rights reserved.