Lead ion activates phosphorylation of electroplax Na+- and K+-dependent adenosine triphosphatase ((NaK)-ATPase) in the absence of sodium ion.

PbCl, in micromolar concentrations stimulates phosphorylation of electroplax microsomal protein in the absence of Nat. Other divalent cations showed little or no such effect. The (Mg’+ + Pb’+)and (Mg”+ + Na+)-dependent membrane-bound protein kinase activities in electroplax particulate preparations exhibit properties in common, including their acid stability, ouabain sensitivity, ATP specificity, and molecular size. It is concluded that the (Mg’+ + Pb’+)-dependent phosphoprotein is part of the Na+-, K+dependent adenosine triphosphatase l(NaK)ATPasel. The Pb’+-dependent product, in contrast to the Na+-dependent one, is insensitive to K+ and the hydrolysis of ATP is thus inhibited.