Accessory subunit of the proton-transporting vacuolar (V)-ATPase protein pump, which is required for luminal acidification of secretory vesicles . Guides the V-type ATPase into specialized subcellular compartments, such as neuroendocrine regulated secretory vesicles or the ruffled border of the osteoclast, thereby regulating its activity . Involved in membrane trafficking and Ca(2+)-dependent membrane fusion . May play a role in the assembly of the V-type ATPase complex (Probable). In aerobic conditions, involved in intracellular iron homeostasis, thus triggering the activity of Fe(2+) prolyl hydroxylase (PHD) enzymes, and leading to HIF1A hydroxylation and subsequent proteasomal degradation . In islets of Langerhans cells, may regulate the acidification of dense-core secretory granules (By similarity).
Subcellular locations: Endoplasmic reticulum membrane, Endoplasmic reticulum-Golgi intermediate compartment membrane, Cytoplasmic vesicle, Secretory vesicle, Synaptic vesicle membrane, Cytoplasmic vesicle, Clathrin-coated vesicle membrane
Not detected in trans-Golgi network.
widely expressed, with highest levels in brain and lowest in liver and duodenum.