The iron transporter fth1p forms a complex with the Fet5 iron oxidase and resides on the vacuolar membrane

Iron transport across the plasmamembrane appears to be a unidirectional pro cess whereby iron uptake is essentially irreversible. One of the major sequ estration sites for iron is the vacuole that stores a variety of metals, ei ther as a mechanism to detoxify the cell or as a reservoir of metal to enab le the cell to grow when challenged by a low iron environment. Exactly how the vacuole contributes to the overall iron metabolism of the cell is uncle ar because mutations that affect vacuolar function also perturb the assembl y of the plasma membrane high affinity transport system composed of a coppe r-containing iron oxidase, Fet3p, and an Fe3+-specific iron transporter, Ft r1p, Here, we characterize the iron transporter homologue Fth1p, which is s imilar to the high affinity plasma membrane iron transporter Ftr1p. We foun d that Fth1p was localized to the vacuolar surface and, like other proteins that function on the vacuole, did not undergo Pep4-dependent degradation. Co-immunoprecipitation experiments showed that Fth1p also associates with t he Fet3p oxidase homologue, Fet5p; and disruption of the PETS gene results in the accumulation of Fth1p in the endoplasmic reticulum, We also found th at loss of this protein complex leads to elevated transcriptional activity of the FET3 gene and compromises the ability of the cell to switch from fer mentative metabolism to respiratory metabolism. Because the Fet5 protein is oriented such that the oxidase domain of Fet5p is lumenal, this complex ma y be responsible for mobilizing intravacuolar stores of iron.