Explain Iron Uptake by Cells?

Iron participates in a large number of biochemical reactions. However, for iron to perform any function, it first needs to be taken up by the cells. Let us then first review iron uptake by cells. Cell membranes contain a protein specific for binding transferrin called 'transferrin receptor'. Transferrin containing two ferric ions, binds to this receptor. Thereafter, iron-transfenin-transferrin receptor complex is internalized by endoyctosis. Within the cell, iron is released from transferrin. It has been shown that intracellular iron concentration more or less remains constant. This intracellular iron homeostasis is maintained by regulating the synthesis and action of proteins involved in the iron acquisition, utilization and storage. When intracellular iron is scarce, cell needs to increase its iron concentration. This is achieved by acquisition of plasma iron and mobilization of storage iron. Also, there is a need to prioritize utilization of iron so that iron is preferentially available for the synthesis of life sustaining iron-containing proteins. Therefore, whenever the intracellular iron concentration is low, the number of transferrin receptors on the cell increase. Further, it is postulated that iron concentration also regulates the synthesis of apoferritin and δ -aminolevulinic acid synthase. The latter is the key enzyme for haem synthesis.