The potassium-transporting ATPase heterodimer (ATP4A/12A:ATP4B) catalyzes the hydrolysis of ATP coupled with the exchange of H+ and K+ ions across the plasma membrane. It is composed of alpha and beta chains. Two human genes encode the catalytic alpha subunit, ATP4A and ATP12A (Maeda et al, 1990; Grishin et al, 1994). ATP4A is responsible for acid production in the stomach. ATP12A is responsible for potassium absorption in various tissues. One human gene encodes the beta subunit, ATP4B (Ma et al, 1991).