Functions as a zinc transporter. Partly regulates cellular zinc homeostasis. Required with ZNT7 for activation of zinc-requiring enzymes, alkaline phosphatases (ALPs). Transports zinc into the lumens of the Golgi apparatus and the vesicular compartments where ALPs locate, thus, converting apoALPs to holoALPs. Required with ZNT6 and ZNT7 for the activation of TNAP (By similarity). 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.