Discovery of a novel cytosolic ferroxidase in rodent enterocytes

Abstract

During iron absorption in the doudenum, iron that exits enterocytes must be oxidized by a membrane bound multi‐copper ferroxidase, hephaestin. We designed experiments to assess Heph activity during iron deficiency and made the unexpected observation that ferroxidase (FOX) activity (by a transferrin‐coupled assay) was present in the cytosol of isolated rodent enterocytes. Several different experimental approaches allowed us to conclude that cytosolic FOX (cytoFOX) activity was not due to contamination with membrane Heph. cytoFOX activity was inhibited by sodium azide (a known FOX inhibitor), pPD (a competing substrate), D‐penicillamine (a copper chelator), and by SDS and heat (showing that it is mediated by a protein). Moreover, activity was increased (~30%) in iron deficient rats but was unchanged in copper deficient rats (in contrast to the reported dramatic reduction of Heph during copper deficiency). Finally, studies done in Heph KO, sla (Heph mutant) and ceruloplasmin (Cp) KO mice proved that cytoFOX activity was not contributed by Heph (or Cp) as activity in enterocyte cytosol was not different between KO/mutant mice and wt littermates. In conclusion, rodent enterocytes contain a cytosolic FOX that may function in transepithelial iron transport, perhaps acting in acidified intracellular vesicles containing the iron exporter ferroportin 1 (Fpn1) and complementing membrane Heph.Grant Funding Source: NIH