Transferrin

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 "apo-transferrin" (see also apoprotein).

Transport mechanism

When a transferrin protein loaded with iron encounters a transferrin receptor on the surface of a cell (importantly, to erythroid precursors in the bone marrow), it binds to it and is consequently transported into the cell in a vesicle. The pH of the vesicle is reduced by hydrogen ion pumps (H⁺ ATPases), causing transferrin to release its iron ions. The receptor (with its ligand, transferrin, bound) 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 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 disorders.

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 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=] , 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.

ee also

* Beta-2 transferrin
* Transferrin receptor
* Total iron-binding capacity
* Transferrin saturation

External links

* [http://macromoleculeinsights.com/transferrin.php The Transferrin Protein]
*

References

Further reading

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=

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