Figure 5

The highly elevated serum transferrin due to lack of effective formation of ferric ion-carbonate-transferrin complex. The dissociation constant of this complex is Kd =10^-22[15]. Iron is absorbed from the duodenal lumen t by divalent-metal transporter 1 (DMT1) after reduced by the cytochrome b, Cyt-b. Intracellular iron enters the labile iron pool (LIP), either exported by iron-regulated protein 1 (IREG1) and then oxidized by hephaestin or, stored in ferritin cores [14] up to 1000 mg Fe. In the presence of bicarbonate ions supplied from anhydrase I, transferrin (Tf) and Fe³⁺ ions form a ternary complex ‘transferrin-bicarbonate-ferric ion complex’ to facilitate transport of ferric ions to be incorporated into hemoglobin [16, 17]. A complex of transferrin receptor 1 (TfR1), the hemochromatosis protein (HFE) and β2-microglobulin, is supposed to act as primarily the iron-biosensor [14].