Protein kinase-dependent phosphorylation of H,K ATPase-containing membranes from rat and pig stomachs.

Previously H,K ATPase preparations from pig stomach were shown to contain intrinsic protein kinase activities which phosphorylated specific tyrosine and serine residues in the N-terminal of the alpha-chain of H,K ATPase (Togawa et al. 1996). In the present investigation, pig H,K ATPase-containing membrane preparations were compared with rat preparations. In contrast to results obtained with the alpha-subunit of H,K ATPase from pig, phosphorylation was not observed in the rat enzyme. Addition of rat preparations to the pig preparations resulted in decreased phosphorylation in pig preparations. To follow the phosphorylation of membrane proteins in vivo, 32P-loaded gastric cells prepared from rat were stimulated with several secretagogues. Proteins with molecular weights of about 120 and 80 kDa were markedly phosphorylated upon stimulation, but the alpha-subunit of H,K ATPase was not. These results suggest that phosphorylation of tyrosine or serine residues of H,K ATPase found in pig H,K ATPase preparations may not be involved in the acid secretion pathway.