Functional regulation of reconstituted Na,K-ATPase by protein kinase A phosphorylation.

Reconstituted Na+,K+-ATPase from either pig kidney or shark rectal glands was phosphorylated by cAMP dependent protein kinase, PKA. The stoichiometry was approximately 0.9 mol P(i)/mol alpha-subunit in the pig kidney enzyme and approximately 0.2 mol P(i)/mol alpha-subunit in the shark enzyme. In shark, Na+,K+-ATPase PKA phosphorylation increased the maximum hydrolytic activity for cytoplasmic Na+ activation and extracellular K+ activation without affecting the apparent K(m) values. In contrast, no significant functional effect after PKA phosphorylation was observed in pig kidney Na+,K+-ATPase.