Co-localization and functional coupling of creatine kinase B and gastric H+/K+-ATPase on the apical membrane and the tubulovesicular system of parietal cells

Abstract

Immunogold labelling of creatine kinase B (BB-CK) and gastric H+/K(+)-ATPase in the parietal cells of the stomach revealed colocalization of these two enzymes on the apical membrane and the membranes of the tubulovesicular system. Upon fractionation of hog parietal cells, a specific 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 pronounced H+/K(+)-ATPase activity in K(+)-loaded vesicles in the presence of phosphocreatine 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(+)-ATPase activity, ATP levels were more than 10-fold higher. Changing the experimental conditions such that ATP levels were the same for both systems resulted in significantly elevated H+/K(+)-ATPase activities in the 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.