COLOCALIZATION AND FUNCTIONAL COUPLING OF CREATINE-KINASE-B AND GASTRIC H+ K+-ATPASE ON THE APICAL MEMBRANE AND THE TUBULOVESICULAR SYSTEM OF PARIETAL-CELLS/

Immunogold labelling of creatine kinase B (BB-CK) and gastric H+/K+-AT Pase in the parietal cells of the stomach revealed colocalization of t hese two enzymes on the apical membrane and the membranes of the tubul ovesicular system. Upon fractionation of hog parietal cells, a specifi c fraction of the BB-CK proteins remained associated with the purified vesicles, in which gastric H+/K+-ATPase is highly enriched. The BB-CK present in this highly purified preparation was able to support prono unced H+/K+-ATPase activity in K+-loaded vesicles in the presence of p hosphocreatine. and ADP, although only low levels of ATP were measured . In contrast, when pyruvate kinase, phosphoenolpyruvate and ADP were used as an ATP-generating system to sustain similar levels of H+/K+-AT Pase activity, ATP levels were more than 10-fold higher. Changing the experimental conditions such that ATP levels were the same for both sy stems resulted in significantly elevated H+/K+-ATPase activities in th e BB-CK/ phosphocreatine system in comparison with the pyruvate kinase /phosphoenolpyruvate system. These results indicate that gastric H+/K-ATPase has preferential access to ATP generated by creatine kinase co -localized on the membranes of the vesicles.