The vacuolar-type H(+)-ATPase (V-ATPase) is responsible for the acidification of endosomes, lysosomes, and other intracellular organelles. It is also involved in hydrogen ion transport across the plasma membrane into the extracellular space. The V-ATPase is a multisubunit complex with cytosolic and transmembrane domains. The cytosolic catalytic domain consists of 3 A subunits and 3 B subunits, which bind and hydrolyze ATP, as well as regulatory accessory subunits.ATP6V1A is V-type proton ATPase catalytic subunit A.