Ferritin: Wikis

  

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ferritin, light polypeptide
Ferritin.png
Structure of the ferritin complex.[1]
Identifiers
Symbol FTL
Entrez 2512
HUGO 3999
OMIM 134790
RefSeq NM_000146
UniProt P02792
Other data
Locus Chr. 19 q13.3-13.4
ferritin, heavy polypeptide 1
Identifiers
Symbol FTH1
Alt. symbols FTHL6
Entrez 2495
HUGO 3976
OMIM 134770
RefSeq NM_002032
UniProt P02794
Other data
Locus Chr. 11 q13
ferritin mitochondrial
Mitochondrial Ferritin.png
Crystallographic structure of mitochondrial ferritin.[2]
Identifiers
Symbol FTMT
Entrez 94033
HUGO 17345
OMIM 608847
RefSeq NM_177478
UniProt Q8N4E7
Other data
Locus Chr. 5 q23.1

Ferritin is a ubiquitous protein that stores iron and releases it in a controlled fashion. The protein is produced by almost all living organisms, including bacteria, algae and higher plants, and animals. In humans, it acts as a buffer against iron deficiency and iron overload.[3]

Ferritin is a globular protein complex consisting of 24 protein subunits and is the primary intracellular iron-storage protein in both prokaryotes and eukaryotes, keeping iron in a soluble and non-toxic form. Ferritin that is not combined with iron is called apoferritin.

Contents

Description

Ferritin is a 450 kDa protein consisting of 24 subunits that is present in every cell type. In vertebrates, these subunits are both the light (L) and the heavy (H) type with an apparent molecular weight of 19 kDA or 21 kDA respectively. In plants and bacteria the complex only consists of the H-chain type. Inside the ferritin shell, iron ions form crystallites together with phosphate and hydroxide ions. The resulting particle is similar to the mineral ferrihydrite. Each ferritin complex can store about 4500 iron (Fe3+) ions.

Some ferritin complexes in vertebrates are hetero-oligomers of two highly-related gene products with slightly different physiological properties. The ratio of the two homologous proteins in the complex depends on the relative expression levels of the two genes.

Mitochondrial ferritin was recently identified as a protein precursor. It is classified as a metal-binding protein which is located within the mitochondria. After the protein is taken up by the mitochondria it can be processed into a mature protein and assemble functional ferritin shells. Its structure was determined at 1.70 angstroms through the use of X-ray diffraction and contains 182 residues. It is 67% helical. The Ramachandran plot [1]shows that the structure of mitochondrial ferritin is mainly alpha helical with a low prevalence of beta sheets.

Function

Ferritin serves to store iron in a non-toxic form, to deposit it in a safe form, and to transport it to areas that it is required.[4]

Free iron is toxic to cells as it acts as a catalyst in the formation of free radicals from reactive oxygen species via the Fenton Reaction.[5] Hence vertebrates? have evolved an elaborate set of protective mechanisms to bind iron in various tissue compartments. Within cells, iron is stored in a protein complex as ferritin or hemosiderin. Apoferritin binds to free ferrous iron and stores it in the ferric state. As ferritin accumulates within cells of the reticuloendothelial system, protein aggregates are formed as hemosiderin. Iron in ferritin or hemosiderin can be extracted for release by the RE cells although hemosiderin is less readily available. Under steady state conditions, the serum ferritin level correlates with total body iron stores; thus, the serum ferritin FR5Rl is the most convenient laboratory test to estimate iron stores.

Because iron is an important mineral in mineralization, ferritin is employed in the shells of organisms such as molluscs to control the concentration and distribution of iron, thus sculpting shell morphology and colouration.[6][7]

Ferritin is also used in materials science as a precursor in making iron nanoparticles for carbon nanotube growth by chemical vapor deposition.

Mitochondrial ferritin has many roles pertaining to molecular function. It participates in ferroxidase activity, binding, iron ion binding, oxidoreductase activity, ferric iron binding, metal ion binding as well as transition metal binding. Within the realm of biological processes it participates in oxidation-reduction, iron ion transport across membranes and cellular iron ion homeostasis.

Diagnostic uses

Serum ferritin levels are measured in patients as part of the iron studies workup for anemia and for restless legs syndrome. The ferritin levels measured have a direct correlation with the total amount of iron stored in the body including cases of anemia of chronic disease.

Normal blood levels are 30-300 ng/mL for males and 15-200 ng/mL for females. ((according to clinical medicine by Kumar & Clark page 428)).[8][9]

Low

If the ferritin level is low, there is a risk for lack of iron, which could lead to anemia. Low ferritin levels (<50 ng/mL) have however been associated with the symptoms of restless legs syndrome, even in the absence of anemia and sickness.[10]

In the setting of anemia, serum ferritin is the most sensitive lab test for iron deficiency anemia.[11]

Low ferritin may also indicate hypothyroidism or vitamin C deficiency.

In a certain study in Paris, France, the level of iron in the blood (measured by ordering a ferritin serum test) has been connected to ADHD in children. Specifically, the lower the iron level, the more severe the ADHD symptoms.[12]

Elevated

If ferritin is high there is iron in excess.

Ferritin is also used as a marker for iron overload disorders, such as hemochromatosis , hemosiderosis and porphyria in which the ferritin level may be abnormally raised.

As ferritin is also an acute-phase reactant, it is often elevated in the course of disease. A normal C-reactive protein can be used to exclude elevated ferritin caused by acute phase reactions.

Ferritin can be elevated during periods of acute malnourishment.[13]

See also

References

  1. ^ PDB 1lb3; Granier T, Langlois d'Estaintot B, Gallois B, Chevalier JM, Précigoux G, Santambrogio P, Arosio P (January 2003). "Structural description of the active sites of mouse L-chain ferritin at 1.2 A resolution". J. Biol. Inorg. Chem. 8 (1-2): 105–11. doi:10.1007/s00775-002-0389-4. PMID 12459904. 
  2. ^ PDB 1r03; Langlois d'Estaintot B, Santambrogio P, Granier T, Gallois B, Chevalier JM, Précigoux G, Levi S, Arosio P (July 2004). "Crystal structure and biochemical properties of the human mitochondrial ferritin and its mutant Ser144Ala". J. Mol. Biol. 340 (2): 277–93. doi:10.1016/j.jmb.2004.04.036. PMID 15201052. 
  3. ^ Iron Use and Storage in the Body: Ferritin and Molecular Representations, Rachel Casiday and Regina Frey, Department of Chemistry, Washington University, St. Louis.
  4. ^ Seckback, J. (1982). "Ferreting out the secrets of plant ferritin - A review". Journal of Plant Nutrition 5: 369–394. doi:10.1080/01904168209362966.  edit
  5. ^ Orino, K.; Lehman, L.; Tsuji, Y.; Ayaki, H.; Torti, S. V.; Torti, F. M. (2001). "Ferritin and the response to oxidative stress". Biochemical Journal 357 (Pt 1): 241. doi:10.1042/0264-6021:3570241. PMID 11415455.  edit
  6. ^ Jackson, D. J.; Wörheide, G.; Degnan, B. M. (2007). "Dynamic expression of ancient and novel molluscan shell genes during ecological transitions". BMC Evolutionary Biology 7: 160. doi:10.1186/1471-2148-7-160.  edit
  7. ^ Yano, M.; Nagai, K.; Morimoto, K.; Miyamoto, H. (2006). "Shematrin: a family of glycine-rich structural proteins in the shell of the pearl oyster Pinctada fucata". Comparative biochemistry and physiology. Part B, Biochemistry & molecular biology 144 (2): 254–262. doi:10.1016/j.cbpb.2006.03.004. PMID 16626988.  edit
  8. ^ Ryan GM, Torelli J (2005). Beyond cholesterol: 7 life-saving heart disease tests that your doctor may not give you. New York: St. Martin's Griffin. ISBN 0-312-34863-0. 
  9. ^ "Ferritin". MedlinePlus Medical Encyclopedia. U.S. National Library of Medicine. http://www.nlm.nih.gov/medlineplus/ency/article/003490.htm. 
  10. ^ Kryger MH, Otake K, Foerster J (March 2002). "Low body stores of iron and restless legs syndrome: a correctable cause of insomnia in adolescents and teenagers". Sleep Med. 3 (2): 127–32. doi:10.1016/S1389-9457(01)00160-5. PMID 14592231. 
  11. ^ Guyatt G, Patterson C, Ali M, Singer J, Levine M, Turpie I, Meyer R (1990). "Diagnosis of iron-deficiency anemia in the elderly". Am J Med 88 (3): 205–9. doi:10.1016/0002-9343(90)90143-2. PMID 2178409. 
  12. ^ Greene MD, Alan (2004-12-17). "Iron and ADHD". http://www.drgreene.com/21_1864.html. Retrieved 2008-08-19. 
  13. ^ Kennedy A, Kohn M, Lammi A, Clarke S (2004). "Iron status and haematological changes in adolescent female inpatients with anorexia nervosa". J Paediatr Child Health 40 (8): 430–2. doi:10.1111/j.1440-1754.2004.00432.x. PMID 15265182. 

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