Rb+ occlusion stabilized by vanadate in gastric H+/K+-ATPase at 25 °C

► The time course of Rb+ occlusion in gastric H+/K+-ATPase was measured at 25 °C. ► Rb+ occlusion was detectable only in the presence of vanadate. ► The enzyme-vanadate complex holding occluded Rb+ is very stable. ► A fraction of the bound Rb+ might not be occluded even in media with vanadate. ► Alamethicin showed to be a suitable permeabilizing agent for gastric vesicles.