Ferritin structure

Ferritin Structure. Ferritin is a large complex protein composed of a protein coat which surrounds a core of polynuclear hydrous ferric oxide (Fe0 0H or Fe203 nH20). Points of contact which have been observed (4) between the inner surface of the protein coat and the iron core may reflect sites of cluster formation and core nucleatlon. 

Theil, E. C- (1987). Ferritin Structure, gene regulation, and cellular function in animals, plants, and microorganisms. Anna. Rex , flrmrtrepn. S6,289-315-... 

The uniqueness of the ferritin structure arises from the metabolic requirement to organize and utilize dissolved iron at concentrations and pH levels that induce precipitation of potentially toxic solid phases. Not only is iron solubilized by micelle encapsulation, but homeostatic control is also maintained. The study of ferritin therefore provides an important example of biological control of solid state reactions that involve the formation and organization of nanometer-size inorganic solids in biological time and space. 

Ferrates, tris(oxalato)-photoreduction, 471 Ferredoxins, 142 redox potentials, 513 Ferri cyanides oxidation by, 504 redox couples, 512 Ferritin structure, 137 Ferrocene history, 3 stereochemistry nomenclature, 131 Ferrocene, l-acetyl-2-methyl-nomenclature, 131 Ferroin... 

Ferritin Structure and Biosynthesis 363 Release of Iron from Ferritin 364 Transferrin 365 Iron Secretion 365 Tissue Iron 365... 

The iron transport and storage proteins transferrin and ferritin (Figures 6 and 7) are responsible for iron homeostasis in organisms after uptake e.g. through the intestine. Ferritins are assemblies of 24 polypeptide subunits, each of which has a four-helix-bundle motif. This protein directs the oxidation of Fe(II) (ferroxidase activity), the translocation of Fe(II) and Fe(III) and the mineralization of iron in the inner core of ferritin. Structures are available from, e.g., vertebrates and bacteria. The latter have two forms of ferritin, one related to the vertebrate structures discussed above, the other comprising iron mainly in the form of heme in addition, there is a dinuclear metal-binding site denoted the ferroxidase site, where the iron binds for oxidation. 

Figure 6.13 shows the Mossbauer spectra of ferritin [51], which is an iron-storage protein consisting of an iron-rich core with a diameter around 8 nm with a structure similar to that of ferrihydrite and which is surrounded by a shell of organic material. At 4.2 K essentially all particles contribute to a magnetically split component, but at higher temperatures the spectra show the typical superposition of a doublet and a sextet with a temperature dependent area ratio. At 70 K the sextet has disappeared since all particles have fast superparamagnetic relaxation at this temperature. 

Addition of sufficient base to give a > 3 to a ferric solution immediately leads to precipitation of a poorly ordered, amorphous, red-brown ferric hydroxide precipitate. This synthetic precipitate resembles the mineral ferrihydrite, and also shows some similarity to the iron oxyhydroxide core of ferritin (see Chapter 6). Ferrihydrite can be considered as the least stable but most reactive form of iron(III), the group name for amorphous phases with large specific surface areas (>340 m2 /g). We will discuss the transformation of ferrihydrite into other more-crystalline products such as goethite and haematite shortly, but we begin with some remarks concerning the biological distribution and structure of ferrihydrite (Jambor and Dutrizac, 1998). 

The detailed high-resolution structure of the non-haem-containing ferritin of E. coli EcFTNA has been recently published (Stillman et al, 2000) and shows considerable structural similarity to human H-chain ferritin (r.m.s. deviation of main chain... 

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