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 similar to 0.9 mole P-i/mole alpha-subunit in the pig kidney enzyme and similar to 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.