Apoferritin crystalline iron core

In vitro a crystalline iron core can be laid down in apoferritin by the addition of an oxidant, such as O2, to an aqueous solution of a ferrous salt and apoferritin (32, 132, 140). The reconstituted core of horse ferritin prepared in the absence of phosphate and with O2 as oxidant is very similar to the native core in terms of its size and Mossbauer properties (85). Electron microscopy, however, reveals that it is less well ordered. Reconstitution in the presence of phosphate leads to smaller cores. Reconstituted A. vinelandii cores in the absence of phosphate were more ordered than were the native cores, and clearly contained ferrihydrite particles and, in some cases, crystal domains (85). Thus the nature of the core is not determined solely by the protein coat the conditions of core formation are also important. This is also indicated by Mossbauer spectroscopy studies of P. aeruginosa cells grown under conditions different than those employed for the large-scale pu-... 

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... 

Reconstitution experiments with apoferritins from animal and bacterial sources, whose native iron-loaded ferritins had crystalline and amorphous cores respectively, have been informative in showing that the core morphology is not determined by the protein shell. For example, Baaghil et al and Mann etalP were able to form crystalline cores in bacterioferritins, and Rohrer formed cores of iron-... 

While the structures of apoferritin and ferritin are fairly well established, the manner in which iron is transported in and out of the protein cavity is still under investigation. It is proposed that iron enters as Fe and is oxidized once inside the protein. The formation of the crystalline core is an example of biomineralization and it is a remarkable achievement of evolution that iron can be stored in mammals effectively as hydrated iron(III) oxide, i.e. a form closely related to rust ... 

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