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 ∼ 0.9 mole P i/mole α-subunit in the pig kidney enzyme and ∼ 0.2 mol P i/mol α-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.