Iron uptake by ferritin

Two proposals have been made for the mechanism of oxidation of apoferritin-bound Fe. In the crystal growth model, the bulk of the Fe is oxidized to Fe(0)(0H) on the surface of the growing crystallite." " It is initiated at catalytic sites on the interior surface of the protein. There is evidence that the mechanism of iron uptake by ferritin changes after the initial uptake. Initial uptake occurs more effectively with O2 as the oxidizing agent, but in the latter stages O2 and KIO3 are equally effective. 

Crichton RR, Herbas A, Chavez-Alba O, Roland F. 1996. Identification of catalytic residues involved in iron uptake by L-chain ferritins. J Biol Inorg Chem 1 567-574. 

Iron can only be resorbed by the bowel in bivalent form (i.e., as Fe " ). For this reason, reducing agents in food such as ascorbate (vitamin C see p. 368) promote iron uptake. Via transporters on the luminal and basal side of the enterocytes, Fe " enters the blood, where it is bound by transferrin. Part of the iron that is taken up is stored in the bowel in the form of ferritin (see below). Heme groups can also be resorbed by the small intestine. 

A significant difference between BFR and H-chain ferritins is the mechanism of iron uptake and core formation. In H-chain ferritins, initial iron uptake takes place by ferrous iron being oxidized at the ferroxidase center and moving into the core, and once a sizeable core has been established, autooxidation at the core surface takes over from the ferroxidase center reaction (see Section 7.2). In BFR, iron uptake takes place in three distinct phases. Phase I is the binding of two ferrous ions per ferroxidase center (48 per protein). Phase 2 corresponds to rapid oxidation at the ferroxidase center according to reactions (7) and (8), where z represents the charge on the protein. ... 

Rapid iron uptake or release by ferritins to form, or breakdown, a Fe(III) core involves redox reactions, as discussed in previous sections. The present section summarizes data regarding measurement of redox properties not involving iron release or uptake. 

The predominant class of intracellular iron-storage compounds is represented by ferritin in eukaryotes and bacterioferritin in prokaryotes (see Iron Proteins for Storage Transport their Synthetic Analogs). In various in vivo Mdssbauer spectroscopic studies on siderophore uptake in fungi, it was realized that siderophores can also function as intracellular iron-storage compounds. In the ascomycete Neurospora crassa, the transport siderophore coprogen represents an intracellular transient iron pool. A major part of coprogen-bound iron is transferred to a... 

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