Plays an important role in cellular zinc homeostasis as a zinc transporter. Regulated in response to zinc availability (By similarity). Colocalized with TFRC in the recycling endosomes. Cycles between endosomal compartments and the plasma membrane in response to zinc availability (By similarity). Defects in SLC39A4 are the cause of bovine hereditary zinc-deficiency (BHZD); also known as lethal trait A46, Adema disease, hereditary parakeratosis, and hereditary thymus hypoplasia. BHZD is a autosomal recessive disease caused by the inability to absorb sufficient zinc. The symptoms are diarrhea, immune system dysfunction, skin lesions and death if untreated. Oral zinc supplementation allows symptom free development of calves (PubMed:16714095). Belongs to the ZIP transporter (TC 2.A.5) family.