SUPEROXIDE-DISMUTASE ACTIVITIES OF AN IRON PORPHYRIN AND OTHER IRON COMPLEXES

The superoxide dismutase (SOD) activities of a number of metal complexes were measured and a mathematical model is proposed which allows their rate constants to be calculated. Fe(CN)64- showed no activity whereas Fe(CN)63- appeared to react stoichiometrically with superoxide. True catalytic SOD activity was apparently shown by chelates of Fe with EDTA [Fe(EDTA)- and Fe(EDTA)2-], with diethylenetriaminepentaacetic acid [Fe(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 tetrakis (4-N-methylpyridyl)porphineiron (III) [FeIIITMpyP], with a rate constant of 3 .times. 107 M-1s-1 at pH 10.1. Exposure of this compound to H2O2 produced in a superoxide-generating system caused its degradation to a product with lower SOD activity, but it could be protected by catalase. H2TMpyP itself showed no SOD activity, nor did its complexes with Zn(II) or Cu(II). CoIIITMpyP showed much lower SOD activity than the Fe(III) complex.