Dcytb (Cybrd1) functions as both a ferric and a cupric reductase in vitro.

MDCK cells expressing an inducible duodenal cytochrome b-green fluorescent protein (Dcytb-EGFP) fusion construct were used to investigate the function of Dcytb. The Dcytb-EGFP protein was targeted correctly to the plasma membrane, and cells displayed increased ferric and cupric reductase activities, which were greatly reduced in the presence of doxycycline. The data suggests that Dcytb plays a physiological role in both iron and copper uptake, through divalent metal transporter 1 (DMT1) and copper transporter 1, respectively. In support of this hypothesis, we show that 59Fe uptake was significantly enhanced in Dcytb-EGFP expressing MDCK cells which endogenously express DMT1.