9.A.9 The Low Affinity Fe2+ Transporter (FeT) Family
The FeT family consists of a single iron-deprivation inducible protein, Fet4p of Saccharomyces cerevisiae as no homologues are currently present in the databases. S. cerevisiae reduces Fe3+ to Fe2+ by an Fe3+ reductase localized to the external surface of the plasma membrane. The Fet4p permease then takes up Fe2+ into the cytoplasm with low affinity (Km = 30 µM). It may also transport Co2+ and Cd2+. The protein has 552 amino acyl residues and six putative transmembrane α-helical spanners. It presumably uses the pmf across the cytoplasmic membrane, but the energy-coupling mechanism is not established. A proton symport mechanism may or may not drive uptake.
The generalized transport reaction catalyzed by the Fet4p permease of S. cerevisiae is:
Fe2+ (out) Æ Fe2+ (in).