The beta subunit of the gastric H(+)/K(+) ATPase pump which transports H(+) ions in exchange for K(+) ions across the apical membrane of parietal cells. Plays a structural and regulatory role in the assembly and membrane targeting of a functionally active pump (By similarity). Within a transport cycle, the transfer of a H(+) ion across the membrane is coupled to ATP hydrolysis and is associated with a transient phosphorylation of the alpha subunit that shifts the pump conformation from inward-facing (E1) to outward-facing state (E2). Interacts with the phosphorylation domain of the alpha subunit and functions as a ratchet, stabilizing the lumenal-open E2 conformation and preventing the reverse reaction of the transport cycle (PubMed:29618813, PubMed:19387495). The ATPase pump is composed of two subunits: alpha (catalytic) and beta (regulatory). Interacts with alpha subunit ATP12A; this interaction is required for the formation of a functionally active pump and targeting at the plasma membrane (By similarity). Interacts (via N-terminus) with alpha subunit ATP4A (via the P-domain) (PubMed:19387495, PubMed:29618813). Localized in the apical canalicular membrane of parietal cells. Stomach. The C-terminal lobe folds into an immunoglobulin-like domain and mediates cell adhesion properties. N-glycosylation is necessary for assembly and functional expression of the pump at the plasma membrane. Parietal cell autoantigen associated with autoimmune gastritis. Belongs to the X(+)/potassium ATPases subunit beta family.