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).



Ahmad, F., Y. Luo, H. Yin, Y. Zhang, and Y. Huang. (2022). Identification and analysis of iron transporters from the fission yeast Schizosaccharomyces pombe. Arch. Microbiol. 204: 152.

Dix, D., J. Bridgham, M. Broderius and D. Eide (1997) Characterization of the FET4 protein of yeast. Evidence for a direct role in the transport of iron. J. Biol. Chem. 272: 11770-11777.

Dix, D.R., J.T. Bridgham, M.A. Broderius, C.A. Byersdorfer and D.J. Eide (1994). The FET4 gene encodes the low affinity Fe(II) transport protein of Saccharomyces cerevisiae. J. Biol. Chem. 269: 26092-26099.

Eide, D. and M. Guerinot (1997). Metal ion uptake in eukaryotes. ASM News 63: 199-205.


TC#NameOrganismal TypeExample

Low affinity Fe2+ transporter


Fet4p of S. cerevisiae


Low affinity iron  (Fe2+)/zinc (Zn2+) transporter, Fet4, of 584 aas and 8 TMSs (Ahmad et al. 2022).

Fet4 of Schizosaccharomyces pombe (Fission yeast)