PHOSPHORYLATION OF THE CATALYTIC SUBUNIT OF NA+,K+-ATPASE INHIBITS THE ACTIVITY OF THE ENZYME

We have examined two distinct protein kinases, cAMP-dependent protein kinase and protein kinase C, for their ability to phosphorylate and regulate the activity of three different types of Na+,K+-ATPase preparation. cAMP-dependent protein kinase phosphorylated purified shark rectal gland Na+,K+-ATPase to a stoichiometry of approximately 1 mol of phosphate per mol of a subunit. Protein kinase C phosphorylated purified shark rectal gland Na+,K+-ATPase to a stoichiometry of approximately 2 mol of phosphate per mol of a subunit. The phosphorylation by each of the kinases was associated with an inhibition of Na+,K+-ATPase activity of about 40-50%. These two protein kinases also inhibited the activity of a partially purified preparation of Na+,K+-ATPase from rat renal cortex and the activity of Na+,K+-ATPase present in preparations of basolateral membrane vesicles from rat renal cortex.