Formation of a Phosphorylated Enzyme Intermediate by the cadA Cd2+-ATPase

Plasmid-mediated resistance to cadmium occurs by means of energy-dependent effiux mediated by a P-ATPase. Formation by the cadA protein of a phosphorylated enzyme intermediate characteristic of members of this class of enzymes was identified by acid pH-sodium dodecyl sulfate-polyacrylamide gel electrophoresis. The formation of the phosphorylated product is dependent upon the presence of the cadA gene product and cadmium. Zinc does not induce labeling, although the determinant has been reported to confer resistance to that cation. The phosphoenzyme product is acid-stable and labile in the presence of alkali or hydroxylamine. Pulse-chase experiments with unlabeled ATP indicate rapid enzyme turnover. The label is also chased in the presence of ADP, suggesting a reversible reaction.