Plays a role in biomineralization; might regulate pH in the magnetosome. Part of the probable 18 gene mamAB operon. Cells have no magnetic response but still make empty magnetosome membranes; magnetosome proteins MamA and MamE localize normally (PubMed:20212111). Deletion of genes mamH to mamV (amb0961 to amb0978) gives cells with no magnetosomes and no magnetic response (PubMed:20212111). This bacteria makes up to 20 cubo-octahedral magnetosomes of about 45 nm in diameter which contain membrane-bound crystals of magnetite (Fe(3)O(4)). Expression of just the minimal mamAB gene cluster (amb0961 to amb0978), including this gene, is sufficient to form a minimal magnetosome chain with small magnetite particles. Belongs to the arsenite-antimonite (ArsB) efflux (TC 2.A.45) family.