AS an endosomal ferrireductase, STEAP3 is required for efficient transferrin-dependent iron uptake in erythroid cells. It participates in erythroid iron homeostasis by reducing Fe(3+) to Fe(2+) and can also reduce of Cu(2+) to Cu(1+), suggesting that it participates in copper homeostasis. STEAP3 uses NAD(+) as acceptor (By similarity). It may play a role downstream of p53/TP53 to interface apoptosis and cell cycle progression. STEAP3 is indirectly involved in exosome secretion by facilitating the secretion of proteins such as TCT.