Functions as a zinc transporter. May be a transporter of zinc into beta cells in order to form insulin crystals. Partly regulates cellular zinc homeostasis. Required with ZNT7 for the activation of zinc-requiring enzymes, alkaline phosphatases (ALPs). Transports zinc into the lumens of the Golgi apparatus and vesicular compartments where ALPs locate, thus, converting apoALPs to holoALPs. Required with ZNT6 and ZNT7 for the activation of TNAP. Homodimer. Homodimerization could enhance the zinc transport efficiency (PubMed:19521526). Forms heterooligomers with ZNT6. Perimeter of granules, localizes to the brush border membrane of the enterocyte. Concentrated in early compartments of the secretory pathway such as COPII-coated vesicles. Ubiquitously expressed. Highly expressed in pancreas, liver and kidney. Expressed abundantly in insulin-containing beta cells, undetectable in other endocrine cell types including glucagon-secreting alpha cells and most acinar cells. Down-regulated by ZNF658 in response to zinc. The histidine-rich loop is essential for ZNT5 and ZNT6 heterooligomeric complexes to activate TNAP. Belongs to the cation diffusion facilitator (CDF) transporter (TC 2.A.4) family. SLC30A subfamily.