Facilitates the accumulation of zinc from the cytoplasm into intracellular vesicles, being a zinc-efflux transporter. May be a major component for providing zinc to insulin maturation and/or storage processes in insulin-secreting pancreatic beta-cells (By similarity). Homodimer. Associated with the insulin and glucagon secretory granules. Expressed in endocrine pancreatic islet alpha and beta cells. Not detected in the brain. Contains a histidine-rich region, HXXXXXHNH-motif, which is a ligand for zinc. Belongs to the cation diffusion facilitator (CDF) transporter (TC 2.A.4) family. SLC30A subfamily.