IRREVERSIBLE ZINC ION INHIBITION OF (Na⁺‐K⁺)‐ADENOSINETRIPHOSPHATASE, Na⁺‐PHOSPHORYLATION, AND K ⁺ ‐p‐NITROPHENYLPHOSPHATASE OF ELECTROPHORUS ELECTRICUS ELECTROPLAX¹

Zinc ion in micromolar concentrations is an irreversible inhibitor of Electrophorus electricus electroplax microsomal (Na + ‐K + )‐ATPase. The rate of inhibition is dependent on [ZnCl 2 ] and the extent of inhibition varies with the ratio of ZnCl 2 to microsomal protein. The same kinetics are observed for inhibition of K + ‐ p ‐nitrophenylphosphatase and steady‐state levels of Na + ‐dependent enzyme phosphorylation. The observations suggest that a Zn 2+ ‐sensitive conformational restraint is important to both kinase and phosphatase activities. The fact that inhibition is irreversible has implications for models seeking to relate zinc effects in tissue to inhibition of (Na + ‐K + )‐ATPase.