Isolation of a gastric phosphoprotein which stimulates acid secretion.

Stimulation of gastric acid secretion is mediated by cAMP which regulates the proton pump through an A-kinase-dependent phosphoprotein. The purpose of this study was to isolate a stimulation-dependent gastric phosphoprotein capable of stimulating acid secretion. Gastric glands were prepared from rabbit gastric mucosa and acid secretion was stimulated with cAMP. A detergent extract of these stimulated gastric membranes was fractionated by gel chromatography and assayed for functional activity by measurement of [14C]-aminopyrine accumulation in permeabilized resting gastric glands or measurement of H(+)-K(+)-ATPase activity in inhibited gastric microsomes. We hereby report isolation of a membrane-bound, A-kinase-dependent phosphoprotein which enhances aminopyrine accumulation in digitonin-permeabilized gastric glands (32%) and stimulates H(+)-K(+)-ATPase activity in gastric microsomes to a level 55% of the maximal stimulation observed in the presence of valinomycin. Incubation of this phosphoprotein with [32P]ATP and the catalytic subunit of A-kinase resulted in [32P] incorporation into a protein which coincided with a single protein band on SDS-PAGE (17,500 Da).