Abstract
A functional approach was utilized to isolate protein effectors from cAMP-stimulated rabbit gastric microsomes capable of stimulating H +-K +-ATPase activity. These studies have resulted in isolation of a cAMP-dependent protein kinase product from rabbit gastric microsomes which is capable of stimulating the proton pump of the parietal cell, H +-K +-ATPase, in inhibited gastric microsomes. This protein is membrane-bound and may be extracted from gastric microsomes only in the phosphorylated state. This phosphoprotein has at least 20 phosphorylation sites and produces enhancement of H +-K +-ATPase activity which equals that induced by the K + ionophore, valinomycin. It would appear, therefore, that cAMP-mediated acid secretion involves phosphorylation of a membrane-bound cAMP-dependent protein kinase substrate in close proximity to the proton pump which produces K + conductance and thereby controls the rate of acid secretion. The degree of phosphorylation of this protein is probably controlled by the activities of cAMP-dependent protein kinase and phosphoprotein phosphatase.
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