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Serum ferritin

Ferritin
Ferritin.png
Structure of the murine ferritin complex 1lb3
Identifiers
Symbol Ferritin
Pfam PF00210
Pfam clan CL0044
InterPro IPR008331
SCOP 1fha
SUPERFAMILY 1fha
ferritin, light polypeptide
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
Crystallographic structure of mitochondrial ferritin.
Identifiers
Symbol FTMT
Entrez 94033
HUGO 17345
OMIM 608847
RefSeq NM_177478
UniProt Q8N4E7
Other data
Locus Chr. 5 q23.1

Ferritin is a universal intracellular protein that stores iron and releases it in a controlled fashion. The protein is produced by almost all living organisms, including algae, bacteria, higher plants, and animals. In humans, it acts as a buffer against iron deficiency and iron overload. Ferritin is found in most tissues as a cytosolic protein, but small amounts are secreted into the serum where it functions as an iron carrier. Plasma ferritin is also an indirect marker of the total amount of iron stored in the body, hence serum ferritin is used as a diagnostic test for iron-deficiency anemia.

Ferritin is a globular protein complex consisting of 24 protein subunits forming a nanocage with multiple metal–protein interactions. It 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.

Ferritin genes are highly conserved between species. All vertebrate ferritin genes have three introns and four exons. In human ferritin, introns are present between amino acid residues 14 and 15, 34 and 35, and 82 and 83; in addition, there are one to two hundred untranslated bases at either end of the combined exons. The tyrosine residue at amino acid position 27 is thought to be associated with biomineralization.

Ferritin is a hollow globular protein of 450 kDa consisting of 24 subunits that is present in every cell type. Typically it has internal and external diameters of about 8 and 12 nm, respectively. 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; their sequences are about 50% homologous. Amphibians have an additional ("M") type of ferritin; the single ferritin of plants and bacteria most closely resembles the vertebrate H-type. Two types have been recovered in the gastropod Lymnaea, the somatic ferritin being distinct from the yolk ferritin (see below). An additional subunit resembling Lymnaea soma ferritin is associated with shell formation in the pearl oyster. Two types are present in the parasite Schistosoma, one in males, the other in females. All the aforementioned ferritins are similar, in terms of their primary sequence, with the vertebrate H-type. In E. coli, a 20% similarity to human H-ferritin is observed. 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.


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