The protein encoded by ATP4A (ATPase H+/K+ Transporting Alpha Subunit) belongs to a family of P-type cation-transporting ATPases. The gastric H+, K+-ATPase is a heterodimer consisting of a high molecular weight catalytic alpha subunit and a smaller but heavily glycosylated beta subunit. This enzyme is a proton pump that catalyzes the hydrolysis of ATP coupled with the exchange of H(+) and K(+) ions across the plasma membrane. It is also responsible for gastric acid secretion. ATP4A encodes a catalytic alpha subunit of the gastric H+, K+-ATPase.