<P> The H / K ATPase is a heterodimeric protein, the product of 2 genes . The gene ATP4A encodes the H / K ATPase α subunit, and is an ~ 1000 - amino acid protein that contains the catalytic sites of the enzyme and forms the pore through the cell membrane that allows the transport of ions . Hydronium ions bind to two active sites present in the α subunit . The α subunit also has a phosphorylation site (Asp). The gene ATP4B encodes the β subunit of the H / K ATPase, which is an ~ 300 - amino acid protein with a 36 - amino acid N - terminal cytoplasmic domain, a single transmembrane domain, and a highly glycosylated extracellular domain . </P> <P> The H / K ATPase β subunit stabilizes the H / K ATPase α subunit and is required for function of the enzyme . The β subunit prevents the pump from running in reverse, and it also appears to contain signals that direct the heterodimer to membrane destinations within the cell, although some of these signals are subordinate to signals found in H / K ATPase α subunit . </P> <P> The structure of H / K ATPase has been determined for humans, dogs, hogs, rats, and rabbits and is 98% homologous across all species . </P> <P> H / K ATPase is a P - type ATPase, a member of the eukaryotic class of P - type ATPases . Like the Ca and the Na / K ATPases, the H / K ATPase functions as an α, β protomer . Unlike other eukaryotic ATPases, the H / K ATPase is electroneutral, transporting one proton into the stomach lumen per potassium retrieved from the gastric lumen . As an ion pump the H / K ATPase is able to transport ions against a concentration gradient using energy derived from the hydrolysis of ATP . Like all P - type ATPases, a phosphate group is transferred from adenosine triphosphate (ATP) to the H / K ATPase during the transport cycle . This phosphate transfer powers a conformational change in the enzyme that helps drive ion transport . </P>

Parietal cell h+/k+ atp pump