Transferrin
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'''Transferrin''' is a [[blood plasma]] [[protein]] for [[iron]] [[ion]] delivery. Transferrin is a [[glycoprotein]], which binds iron very tightly but reversibly. Although iron bound to transferrin is less than 0.1% (4 mg) of the total body iron, dynamically it is the most important iron pool, with the highest rate of turnover (25 mg/24 h). Transferrin has a molecular weight of around 80 kiloDaltons and contains 2 specific high affinity Fe(III) binding sites. The affinity of transferrin for Fe(III) is extremely high (10^23 M^-1 at pH 7.4) but decreases progressively with decreasing pH below neutrality.
When not bound to iron, it is known as "apotransferrin" (see also [[apoprotein]]).
== Transport mechanism ==
When a transferrin protein loaded with iron encounters a [[transferrin receptor]] on the surface of a [[cell (biology)|cell]] (importantly, to erythroid precursors in the bone marrow), it binds to it and is consequently transported into the cell in a [[vesicle (biology)|vesicle]]. The H<sup>+</sup> ATPase of the cell will decrease the pH of the vesicle, causing transferrin to release its iron ions. The receptor with its ligand bound to it is then transported through the [[endocytic cycle]] back to the cell surface, ready for another round of iron uptake.
Each transferrin molecule has the ability to carry two iron ions in the [[ferric]] form (Fe3+).
The [[gene]] coding for transferrin in humans is located in [[chromosome]] band 3q21. Research on [[King snake|king snakes]] by Dessauer and Zwiefel in 1981 revealed that the inheritance of transferrin is a [[codominant]] trait.
Medical professionals may check serum transferrin level in [[iron deficiency]], [[hemochromatosis]] and other [[iron overload disorder]]s.
== Immune system ==
Transferrin is also associated with the innate immune system. Transferrin is found in the [[mucosa]] and binds iron, thus creating an environment low in free iron, where few bacteria are able to survive. The levels of transferrin decreases in inflammation<ref name=Ritchie> {{cite journal |author=Ritchie RF, Palomaki GE, Neveux LM, Navolotskaia O, Ledue TB, Craig WY |title=Reference distributions for the negative acute-phase serum proteins, albumin, transferrin and transthyretin: a practical, simple and clinically relevant approach in a large cohort |journal=J. Clin. Lab. Anal. |volume=13 |issue=6 |pages=273–9 |year=1999 |pmid=10633294 |doi=}}</ref>, seeming contradictory to its function.
A decrease in the amount of transferrin would result in hemosiderin in the liver.
== Other effects ==
The metal binding properties of transferrin have a great influence on the biochemistry of [[plutonium]] in humans.
Transferrin has a bacteriocidal effect on bacteria, in that it makes Fe3+ unavailable to the bacteria.
==Pathology==
A deficiency is associated with [[atransferrinemia]].
==See also==
* [[Beta-2 transferrin]]
* [[Transferrin receptor]]
* [[Total iron-binding capacity]]
* [[Transferrin saturation]]
==External links==
* [http://macromoleculeinsights.com/transferrin.php The Transferrin Protein]
* {{MeshName|Transferrin}}
==References==
{{reflist}}
==Further reading==
{{refbegin | 2}}
{{PBB_Further_reading
| citations =
*{{cite journal | author=Hershberger CL, Larson JL, Arnold B, ''et al.'' |title=A cloned gene for human transferrin |journal=Ann. N. Y. Acad. Sci. |volume=646 |issue= |pages= 140–54 |year= 1992 |pmid= 1809186 |doi= }}
*{{cite journal | author=Bowman BH, Yang FM, Adrian GS |title=Transferrin: evolution and genetic regulation of expression |journal=Adv. Genet. |volume=25 |issue= |pages= 1–38 |year= 1989 |pmid= 3057819 |doi= }}
*{{cite journal | author=Parkkinen J, von Bonsdorff L, Ebeling F, Sahlstedt L |title=Function and therapeutic development of apotransferrin |journal=Vox Sang. |volume=83 Suppl 1 |issue= |pages= 321–6 |year= 2003 |pmid= 12617162 |doi= }}
}}
{{refend}}
[[Category:Chemical pathology]]
{{Cell-biology-stub}}
{{Iron-binding proteins}}
{{Beta globulins}}
{{Acute phase proteins}}
{{Iron metabolism}}
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[[pl:Transferyna]]
[[pt:Transferrina]]
[[sv:Transferrin]]
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