How are cytochrome b561 electron currents controlled by membrane voltage and substrate availability?

Direct recordings of electron currents mediated by cytochromes b561 (CYB561) are not available yet, despite the importance of these proteins in a variety of physiological functions, including neurotransmitter synthesis and dietary iron uptake. Here, we used the two-electrode voltage-clamp technique applied to Xenopus oocytes to demonstrate, for the first time, the generation of electron currents by a Drosophila member of the CYB561 superfamily named stromal cell-derived receptor 2 (SDR2). This experimental method, along with the theoretical development of a three-state kinetic model, supports the hypothesis that electron donor/acceptor concentrations and transmembrane voltage mutually control SDR2-mediated electron transport activity in a complex but predictable manner.