Apoferritin iron deposition

We assume that all substances involved in ferritin iron deposition (Fe2+, Fe3+, 02) need to gain access to the interior of the apoferritin protein shell. The most likely pathway is via the three-fold channels, which would involve passing through the 12 A long channel, and then traverse a further distance of 8 A along a hydrophilic pathway from the inside of the... 

Chasteen ND, Antanaitis BC, Aisen P. 1985. Iron deposition in apoferritin evidence for the formation of a mixed-valence binuclear iron complex. J Biol Chem 260 2926-2929. 

Iron can be deposited in ferritin by allowing apoferritin to stand with an Fe(II) salt and a suitable oxidant, which may be 02. Physiological transfer of Fe(III) from transferrin to ferritin is thought to require prior reduction to Fe(II). The reoxidation by 02 to Fe(III) for deposition in the ferritin core (Eq. 16-2) is catalyzed by ferrooxidase sites located in the centers of the helical bundles of the H-chains.70-73... 

The inner cavity is filled with small crystalline particles of composition [Fe(0)(0H)]g-[Fe(0)(0P03H2)], which is 57% iron and contains up to about 4500 iron atoms per ferritin molecule. While the core stores iron as Fe111, it is generally accepted that deposition and mobilization involve Fe11. Apoferritin rapidly accumulates iron in a solution containing Fe11 and 02, but Fe111... 

Ferritin has also been compared with iron-dextran by the EXAFS technique.1108 The apoferritin controls the deposition of the core. Reconstitution of ferritin under a range of conditions always gives the same structure, which is not the case in the absence.of apoferritin. There are metal-binding sites on the protein shell. There is evidence for the binding of iron to apoferritin, probably by carboxyl groups, but there is little detailed information on these sites.1098 On the other hand, other metal ions inhibit the formation of ferritin and may do this by binding at or close to the iron sites. Of most significance appear to be results on Tb3+, Zn2+ and V02+,... 

The deposition of Fe into apoferritin using 02 as the oxidant shows that only 3-4% of the oxygen atoms in the core were derived from O2, irrespective of the amount of iron added. Use of H2 0 as solvent confirms that nearly all the oxygen atoms in the core were derived from the solvent. This work gave a stoichiometry of two Fe per 02." It is known that this stoichiometry can vary from 2 1 to 4 1 under different conditions. In the case of the lower stoichiometry, superoxide or peroxide must be produced, although they have not been detected. 

---