A direct demonstration of the catalytic action of superoxide dismutase through the use of pulse radiolysis.

Superoxide dismutase catalyzes the decay of 0~~, generated by pulse radiolysis. The enzymatic reaction was 6rst order with respect to enzyme and to 0~~ and the rate constant, which was 2.3 X lo9 M-' s-l at pH 7.0 and ZO-25”, was not much affected by pH, in the range 4.8 + 9.5. Boiling the enzyme or reversibly removing its copper prosthetic group caused loss of catalytic activity. EDTA had no effect on the enzyme-catalyzed dismutation of superoxide radicals, but did eliminate catalysis by Cu++.