Ser-27, Tyr-10 and Tyr-7 in the alpha-chain of pig stomach H+,K(+)-ATPase as Ca(2+)-dependent phosphorylatable sites by intrinsic and extrinsic protein kinases.

When pig stomach membrane H+,K(+)-ATPase preparations were incubated with [gamma-32P]ATP, Mg2+ and Ca2+, reversible phosphorylation of specific Tyr and Ser residues in the N-terminal alpha-chain of H+,K(+)-ATPase occurred without any detectable phosphorylation in other regions of the alpha-chain. Mild tosylphenylalanyl chloromethyl ketone trypsin treatment followed by reverse-phase column chromatography yielded three radioactive peptide peaks. The first peak contained both Tyr10(32P) and Tyr7(32P) and the second peak contained Tyr10(32P). The third peak contained Ser27(32P) which was also obtained after trypsin treatment of partially purified H+,K(+)-ATPase preparations phosphorylated with protein kinase-C + Ca2+ or protein kinase-A. This is the first demonstration of Ca2(+)-dependent phosphorylation of the alpha-chain of H+,K(+)-ATPase by protein kinases.