No evidence that copper is a transported substrate of the iron transporter DMT1

Abstract

Divalent metal‐ion transporter 1 (DMT1) is essential for intestinal iron absorption and erythroid iron utilization. Mechanisms for the cellular uptake of copper are less clearly understood. We have previously demonstrated that DMT1 exhibits promiscuity towards a broad range of divalent metal ions that includes Cd2+, Co2+, Fe2+, Mn2+, Ni2+ and VO2+ but not copper; however, other investigators have claimed that DMT1 transports copper. Here, we further tested the hypothesis that copper is a transported substrate of DMT1 in vitro by measuring metal‐ion fluxes and currents in RNA‐injected Xenopus oocytes expressing DMT1. Expression of DMT1 in oocytes stimulated over 80‐fold the uptake of 2 μM 55Fe2+ at pH 6.0 (P < 0.001) but transport of 64Cu1+ or 64Cu2+ did not differ from control (P ≥ 0.71); however, Cu1+ inhibited DMT1‐mediated 55Fe2+ uptake in a competitive fashion (Ki ≈ 58 μM). In both control oocytes and oocytes expressing DMT1, Cu1+ evoked an inward current that markedly differed from typical DMT1‐dependent transport currents. Cu2+ did not evoke a current. Whereas DMT1 substrates (e.g. Fe2+ and Cd2+)—but not Cu1+—abolished the presteady‐state currents observed in the absence of metal ion, Cu2+ instead altered the time constant of the decay and did not abolish the transient currents. We conclude that Cu1+ and Cu2+ are capable of interacting with DMT1 but that neither is a transported substrate.