Membrane (Na +K)ATPase isolated from rat brain was preincubated in a medium in which superoxide radicals were generated enzymatically. Exposure to superoxide radicals caused an irreversible inactivation, which could be prevented by further addition of superoxide dismutase. (Na + K)ATPase was also protected by addition of allopurinol, a xanthine oxidase inhibitor, during preincubation. The K-activated nitrophenylphosphatase associated with (Na + K)ATPase was also found to be inactivated by preincubation with superoxide radicals, which could be prevented by superoxide dismutase.
Superoxide dismutase activity was determined by the adrenalin method in bovine erythrocytes separated according to age. Progressive loss of the enzyme activity was found, down to ca 65% of that of the youngest cells.
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