Superoxide dismutase activity of low molecular weight Cu2+‐chelates studied by pulse radiolysis

The discovery of an accelerated superoxide dismutation [ 1 ] using erythrocuprein led to an overwhelming number of studies on this metalloprotein (for a review see ref. [2] ). The mechanism of this enzymic catalysed reaction was successfully studied by pulse radiolysis [3-51. It was intriguing to realize that erythrocuprein which has apparently evolved [6] to perform so simple a reaction proved, in some ways, far from simple. The situation turned out even more complicated with the knowledge that free Cu2 * catalyses superoxide dismutation in acidic media in a much faster way compared to the reactivity of erythrocuprein under physiological pH conditions [7] . Furthermore, it was demonstrated that low molecular weight copper chelates display marked superoxide dismutase activity at physiological pH values employing the cytochrome c reductase assay [X] . In this context it was of high importance to measure the rate constants for reaction between some of these cupric-peptide chelates and the superoxide ion generated by pulse radiolysis at pH 7 5. The reaction of chelated Cu2 * with superoxide was very fast throughout. The respective second order rate constants of either equivalent of Cu2+ ranged from 0.6 X IO9 M-r see-’ (Cu(ly~)~) up to 1.3 X IO9 M-’

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