H+-ATPaseA ubiquitously expressed enzyme transporter present in the plasma membrane, as well as in endomembrane organelles—vacuoles, lysosomes, endosomes, the Golgi apparatus, chromaffin granules and coated vesicles—which acidifies intracellular compartments in eukaryotic cells. Acidification is necessary for such intracellular processes as protein sorting, protein degradation and coupled transport, zymogen activation, receptor-mediated endocytosis and synaptic vesicle proton gradient generation; it also plays a role in bone reabsorption and in sperm motility and maturation. H+-ATPase is a multisubunit complex composed of two domains: a cytosolic V1 domain responsible for ATP hydrolysis and a transmembrane V0 domain responsible for protein translocation.
Mechanisms of regulating H+-ATPase activity:
• Recycling of H+-ATPase-containing vesicles to and from the plasma membrane;
• Glucose-sensitive assembly/disassembly of the holoenzyme complex.
H+-ATPase mutations in the A3 gene cause recessive osteopetrosis; they have been implicated in tumour metastasis.