A Novel P-Type Cl −-Stimulated ATPase: Phosphorylation and Specificity

Utilizing a proteoliposomal preparation containing Cl −-ATPase, it was demonstrated that [γ- 32P]ATP-induced phosphorylation of this pump is by way of a relatively low binding affinity while protein dephosphorylation was accelerated by increasing concentrations of unlabeled ATP. Ca 2+ and Mn 2+ were also shown to stimulate phosphorylation of the enzyme, but to a much lesser extent than Mg 2+. Orthovanadate inhibition of enzyme phosphorylation was directly related to its concentration. These results suggested that the Cl −-pump was a P-type ATPase similar to that found in plants and fungi based upon its low-affinity phosphorylation kinetics.