a membrane-bound enzyme occurring on the secretory surfaces of parietal cells that uses the energy derived from the hydrolysis of ATP to drive the exchange of ions across the cell membrane, secreting acid into the gastric lumen. Protons and chloride ions are pumped against gradients across the apical membranes of activated parietal cells into the gastric lumen in exchange for potassium ions. See also adenosine triphosphatase.


widely distributed enzyme consisting of two large α-subunits and two smaller β-subunits, whose function is to transport Na+ and K+ against their concentration gradients using hydrolysis of ATP as the thermodynamic couple. The stoichiometry of exchange is two K+ for every three Na+ pumped. Often called the sodium pump.