Accessory component of the proton-transporting vacuolar (V)- ATPase protein pump involved in intracellular iron homeostasis. In aerobic conditions, required for intracellular iron homeostasis, thus triggering the activity of Fe(2+) prolyl hydroxylase (PHD) enzymes, and leading to HIF1A hydroxylation and subsequent proteasomal degradation. Necessary for endolysosomal acidification and lysosomal degradation (PubMed:28296633). May be involved in Golgi homeostasis (PubMed:26833332). {ECO:0000269|PubMed:26833332, ECO:0000269|PubMed:28296633}. This is the function of ENSG00000136710 (VMA22, vacuolar ATPase assembly factor VMA22).