Mammalian iron absorption requires the transfer of iron across both the apical and the basolateral membranes of duodenal enterocytes. Divalent metal transporter 1 (DMT1), located on the apical brush-border membrane, mediates the uptake of reduced, nonheme iron (Fe2+). A portion of this iron is retained within the cell for use or for storage in ferritin; the remainder is transferred to the circulation by ferroportin, a nonheme-iron exporter. Released iron must be oxidized to bind to its plasma carrier protein, transferrin. A recent study suggests that the absorption of heme iron is mediated by HCP1,2 also expressed on the apical membrane. At least some heme is likely catabolized by heme oxygenase. This process may require the movement of heme into a membrane-bound subcellular compartment. Inorganic iron released from heme probably has the same fate as absorbed nonheme iron. The existence of two mammalian heme exporter proteins, Bcrp and FLVCR, raises the possibility that heme may transit the enterocyte intact and be exported into the serum.New England Journal of Medicine kirjoittaa 8.12.05 raudan imeytymisestä.