Phosphorylation of H,K-ATPase alpha-subunit in microsomes from rabbit gastric mucosa by cAMP-dependent protein kinase

A 100-kDa protein that is a main component of the microsomal fraction from rabbit gastric mucosa is phosphorylated by cAMP-dependent protein kinase (P KA) in the presence of 0.2% Triton X-100. Microsomes from rabbit gastric mu cosa possess activity of H,K-ATPase but not activity of Na,K-ATPase. Incuba tion of microsomes with 5 mu M fluorescein 5'-isothiocyanate (FITC) results in both an inhibition of H,K-ATPase and labeling of a protein with an elec trophoretic mobility corresponding to the mobility of the protein phosphory lated by PKA. The data suggest that the alpha-subunit of H,K-ATPase can be a potential target for PKA phosphorylation.