Ferritin, an iron-storage protein

Iron is one of the most important elements in biology. In hemoglobin, it allows the binding of molecular oxygen. Iron plays an important role in the active centers of many enzymes. The total quantity of iron in the human body is about 4g. Each day, the body eliminates approximately 1 or 2 mg of iron. 

This loss is compensated by the alimentation. 70 % of the body iron is contained in hemoglobin. Transferrin ensures the transport of iron, while ferritin and hemosiderin are used for the storage of iron in a non-toxic form ferritin is indeed able to transform the highly toxic Fe(II) in to the less toxic Fe(III). 

Ferritin is present in numerous living species, from bacteria to elephant. In humans, it is mainly located in the liver, in the spleen, in the bone marrow, and in the extrapyramidal nuclei of the brain (putamen, globus pallidus, caudate and substantia nigra). 

Ferritin is composed by the arrangement of 24 protein subunits, which results in a hollow shell of 8 nm inner diameter and 13 nm outer diameter (Fig. 13). Ferritin from vertebrates have two types of subunits heavy (H) and light (L). The subunit composition of human ferritins depends on the origin of the protein H2L22 for liver ferritin, H20L4 for muscle ferritin, etc. Access channels are formed by the intersection of subunits. The 8 channels located at the intersection of three subunits are hydrophilic while the 6 channels located at the intersection of 4 subunits are hydrophobic. The empty protein is called apoferritin (30). 

Fe(II) penetrates inside the spherical shell by the hydrophilic channels. After an oxidation on ferroxidase sites, located on H subunits, Fe(III) iron ions migrate to a nucleation site, situated on L subunits, where a crystal of hydrated iron oxide grows. Up to 4500 Fe(III) can be stored inside this mineral phase (31). The number of iron atoms contained in the ferritin molecule is called the loading factor (LF). 

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G. Application of the relaxometric study of super-paramagnetic particles II. Ferritin, an iron-storage protein... 

Ferrihydrite is the iron oxide with the most widespread distribution in living organisms. In the form of ferritin, an iron storage protein, it is found in all organisms from bacteria through to man (in heart, spleen and liver). It occurs in plants as phytoferritin (review by Seckback, 1982). Ferritin plays a key role in iron metabolism it maintains... 

Formation of a site-specific mRNA-protein complex is involved in the translational control of the biosynthesis of ferritin, an iron storage protein, which is stimulated in response to the presence of iron. In this instance, a cytoplasmic repressor protein of 85 kDa binds to a highly conserved 28-nucleotide stem-loop structure in the 5 untranslated region of ferritin mRNAs in the absence of iron. In the presence of iron, the protein dissociates from the mRNA, which is then available for translation. A similar loop motif occurs in the 3 untranslated region of transferrin receptor mRNA, which is also subject to translational control by an iron-responsive repressor. 

E.s.r. studies at liquid-helium temperatures have given new information relating to the structure and mechanism of action of xanthine oxidase, and further studies have been made on the rapid and slow changes in intensity of the two molybdenum(v) signals during anaerobic reduction of the enzyme. The structure and function of ferritin, an iron storage protein which seems to have close links with xanthine oxidase, have been reviewed. ... 

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. 

One way is to label the pre-existing vesicles, and then follow the destiny of the label in the vesicle size distribution. The label that has been used to this aim is ferritin, which has been entrapped into vesicles. Ferritin is an iron-storage protein in plants and mammals, and consists of a hollow protein shell of c. 12 nm containing... 

Iron is best absorbed in the ferrous form or as heme. It is believed that transferrin, transported into the small intestine from the liver via bile, carries iron into the intestinal mucosal cells. Though about 16 mg of iron enter these cells every day, only 1-2 mg finds its way into the bloodstream. The rest remains bound to an iron storage protein called ferritin and is eventually lost in the feces in the normal sloughing-off process. Iron absorption also depends on its bioavail-... 

One striking similarity between iron metabolism in animals and bacteria is that both contain ferritin (63). Bacterial ferritin, or bacfer, resembles ferritin in a number of respects (Section IV), but a key difference is that bacfer is also a 6-type cytochrome (129), cytochrome bi (126). Thus the question arises Is it primarily a cytochrome or primarily an iron storage protein This question opens up a large number of avenues of research, some of which are described in Section IV, that we believe will help define further how animal ferritin functions. One important area is that of genetic control of bacfer expression. 

Iron is an essential component of man s biochemistry but, in common with other elements, becomes toxic when in excess (3, ) This arises in part because of the tendency of iron(III) to separate in tissues as very insoluble hydroxide and phosphate salts at the physiological pH and higher unless bound to transferrin, the iron transport protein, or to ferritin, the iron storage protein. Iron absorption via the diet is physiologically controlled, but the body has no regulatory mechanisms for eliminating a toxic excess Introduced by accidental overdose or by multiple transfusions. 

Hemosiderin an iron storage protein of the mammalian organism, functionally related to Ferritin (see). H. is deposited in the liver and spleen (hemosiderosis), particularly in diseases associated with increased blood destruction, such as pernicious anemia, or with increased iron resorption (hemochromatosis), or even in hemorrhages Most of the deposits are located in the liver, which may contain up to 50 g H., compared with the normal content of 120 to 300 mg H. H. from horse spleen consists of 26-34 % iron(III), and up to 35 % protein (aposiderin). The rest is made up of octasubstituted porphyrin, mucopolysaccharides and fatty acid esteis. 

Ferritin is an iron-storage protein, which keeps iron in a safe form within a protein shell. The protein shell of mammalian ferritin is composed of 24 subunits of heavy (H)and light (L) amino acid chains. The external diameter of the protein shell is about 12 nm, and the diameter of the internal cavity is about 7 nm. Inside this cavity up to 4500 ions of iron may be located. Most of the ferritin molecules are not full, but contain varying amounts of iron [IT]. 

Supramolecular preorganization requires the construction of an organized reaction environment prior to the actual mineralization event. In general this involves the self-assembly of lipid vesicles that provide an enclosed space for mineralization. Sometimes a protein construct is made for encapsulating the mineral. The latter is the case of ferritin, the iron storage protein in mammals. Several... 

C20-0105. The iron storage protein ferritin usuaiiy is neither empty of iron nor fiiied to capacity. Why is this situation advantageous for an organism ... 

Iron is stored in these proteins in the ferric form, but is taken up as Fe2+, which is oxidized by ferroxidase sites (a more detailed account of iron incorporation into ferritins is given later in this chapter). As we point out in Chapter 13, ferritins are members of the much larger diiron protein family. After oxidation, the Fe3+ migrates to the interior cavity of the protein to form an amorphous ferric phosphate core. Whereas the ferritins in bacteria appear to fulfil the classical role of iron-storage proteins, the physiological role of bacterioferritins is less clear. In E. coli it seems unlikely that bacterioferritin plays a major role in iron storage. 

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