IDENTIFICATION OF THE PHOSPHORYLATION SITE FOR CAMP-DEPENDENT PROTEIN-KINASE ON NA-ATPASE AND EFFECTS OF SITE-DIRECTED MUTAGENESIS(,K+)

Phosphorylation of purified Na+,K+-ATPase by cAMP-dependent protein ki nase (protein kinase A) decreases the activity of this enzyme. We have now shown, using several experimental approaches, that a highly conse rved seryl residue on the catalytic (alpha) subunit of Na+,K+-ATPase, corresponding to Ser(943) of the rat alpha 1 isoform, is the phosphory lation site for protein kinase A. cDNAs corresponding to wild-type Na,K+-ATPase and Na+,K+-ATPase in which Ser(943) was mutated to Ala were transfected into COS cells. Treatment of the transfected cells with f orskolin plus 3-isobutyl-1-methylxanthine resulted in a decrease in th e activity of the wild-type enzyme but not in that of the mutated enzy me. The results suggest that, in intact cells, the activity of the Na,K+-ATPase is regulated in part by signal transduction pathways that u se protein kinase A-dependent phosphorylation of the Na+,K+-ATPase alp ha subunit.