 V-ATPase dependent organelle acidification is necessary for such intracellular processes as protein sorting, zymogen activation, receptor-mediated endocytosis, and synaptic vesicle proton gradient generation.V-ATPase is composed of a cytosolic V1 domain and a transmembrane V0 domain.The V1 domain consists of three A, three B, and two G subunits, as well as a C, D, E, F, and H subunit.