Together with SLC30A6 forms a functional proton-coupled zinc ion antiporter mediating zinc entry into the lumen of organelles along the secretory pathway (PubMed:11904301, PubMed:15525635, PubMed:15994300, PubMed:19366695, PubMed:22529353). By contributing to zinc ion homeostasis within the early secretory pathway, regulates the activation and folding of enzymes like alkaline phosphatases and enzymes involved in phosphatidylinositol glycan anchor biosynthesis (PubMed:15525635, PubMed:15994300, PubMed:16636052, PubMed:35525268). Through the transport of zinc into secretory granules of pancreatic beta-cells, plays an important role in the storage and secretion of insulin (PubMed:11904301). {ECO:0000269|PubMed:11904301, ECO:0000269|PubMed:15525635, ECO:0000269|PubMed:15994300, ECO:0000269|PubMed:16636052, ECO:0000269|PubMed:19366695, ECO:0000269|PubMed:22529353, ECO:0000269|PubMed:35525268}. [Isoform 2]: Zinc ion:proton antiporter mediating influx and efflux of zinc at the plasma membrane. {ECO:0000269|PubMed:11937503, ECO:0000269|PubMed:17355957}. This is the function of SLC30A5 (solute carrier family 30 member 5, ENSG00000145740).