FIG. 4.
Iron transport across the enterocyte. Oxidized Fe3+ iron in the food is reduced by the ferrireductase Dcytb on the AP plasma membrane to the Fe2+ form for transport by DMT1 to the cytosol. Heme is taken up via heme carrier protein 1 and is degraded by HO-1 to release Fe2+ iron. A receptor for ferritin has also been described on the AP plasma membrane. Iron from these sources enters the common labile iron pool, and is either stored in ferritin or exported from the baso-lateral membrane by the Fpn/Hp complex that oxidizes exported Fe2+ iron to the Fe3+ form for loading to plasma Tf. Dcytb, duodenal cytochrome b; DMT1, divalent metal transporter 1.