Editing Transferrin (section)

{{Short description|Mammalian protein found in Homo sapiens}}
{{cs1 config|name-list-style=vanc}}
{{Infobox_gene}}
{{Infobox protein family
| Symbol = Transferrin
| Name = Transferrin
| image =
| width =
| caption =
| Pfam= PF00405
| InterPro= IPR001156
| SMART=
| Prosite = PDOC00182
| SCOP = 1lcf
| TCDB =
| OPM family=
| OPM protein= 
| PDB=
}}

'''Transferrins''' are [[glycoprotein]]s found in [[vertebrate]]s which bind and consequently mediate the transport of [[iron]] (Fe) through [[blood plasma]].<ref name="PUB00001349">{{Cite journal |vauthors=Crichton RR, Charloteaux-Wauters M |date=May 1987 |title=Iron transport and storage |journal=European Journal of Biochemistry |volume=164 |issue=3 |pages=485–506 |doi=10.1111/j.1432-1033.1987.tb11155.x |pmid=3032619|doi-access=free }}</ref> They are produced in the [[liver]] and contain binding sites for two [[Iron(III)|Fe<sup>3+</sup>]] ions.<ref>{{cite journal | vauthors = Hall DR, Hadden JM, Leonard GA, Bailey S, Neu M, Winn M, Lindley PF | title = The crystal and molecular structures of diferric porcine and rabbit serum transferrins at resolutions of 2.15 and 2.60 A, respectively | journal = Acta Crystallographica. Section D, Biological Crystallography | volume = 58 | issue = Pt 1 | pages = 70–80 | date = January 2002 | pmid = 11752780 | doi = 10.1107/s0907444901017309 | bibcode = 2002AcCrD..58...70H }}</ref> Human transferrin is encoded by the ''TF'' [[gene]] and produced as a 76 [[Dalton (unit)|kDa]] glycoprotein.<ref name="pmid6585826">{{cite journal | vauthors = Yang F, Lum JB, McGill JR, Moore CM, Naylor SL, van Bragt PH, Baldwin WD, Bowman BH | display-authors = 6 | title = Human transferrin: cDNA characterization and chromosomal localization | journal = Proceedings of the National Academy of Sciences of the United States of America | volume = 81 | issue = 9 | pages = 2752–6 | date = May 1984 | pmid = 6585826 | pmc = 345148 | doi = 10.1073/pnas.81.9.2752 | bibcode = 1984PNAS...81.2752Y | doi-access = free }}</ref><ref name="Kawabata_2019">{{cite journal | vauthors = Kawabata H | title = Transferrin and transferrin receptors update | journal = Free Radical Biology & Medicine | volume = 133 | pages = 46–54 | date = March 2019 | pmid = 29969719 | doi = 10.1016/j.freeradbiomed.2018.06.037 | s2cid = 49674402 }}</ref>

Transferrin [[glycoprotein]]s bind iron tightly, but reversibly. Although iron bound to transferrin is less than 0.1% (4&nbsp;mg) of total body iron, it forms the most vital iron pool with the highest rate of turnover (25&nbsp;mg/24 h). Transferrin has a molecular weight of around 80 [[atomic mass unit|kDa]] and contains two specific high-affinity [[Fe(III)]] binding sites. The affinity of transferrin for Fe(III) is extremely high ([[association constant]] is 10<sup>20</sup> M<sup>−1</sup> at pH 7.4)<ref name="pmid204636">{{cite journal | vauthors = Aisen P, Leibman A, Zweier J | title = Stoichiometric and site characteristics of the binding of iron to human transferrin | journal = The Journal of Biological Chemistry | volume = 253 | issue = 6 | pages = 1930–7 | date = March 1978 | doi = 10.1016/S0021-9258(19)62337-9 | pmid = 204636 | doi-access = free }}</ref> but decreases progressively with decreasing [[pH]] below neutrality. Transferrins are not limited to only binding to iron but also to different metal ions.<ref>{{cite journal | vauthors = Nicotra S, Sorio D, Filippi G, De Gioia L, Paterlini V, De Palo EF, Grandori R, Tagliaro F, Santambrogio C | display-authors = 6 | title = Terbium chelation, a specific fluorescent tagging of human transferrin. Optimization of conditions in view of its application to the HPLC analysis of carbohydrate-deficient transferrin (CDT) | journal = Analytical and Bioanalytical Chemistry | volume = 409 | issue = 28 | pages = 6605–6612 | date = November 2017 | pmid = 28971232 | doi = 10.1007/s00216-017-0616-z | s2cid = 13929228 }}</ref> These glycoproteins are located in various bodily fluids of vertebrates.<ref name="MacGillivray_1998">{{cite journal | vauthors = MacGillivray RT, Moore SA, Chen J, Anderson BF, Baker H, Luo Y, Bewley M, Smith CA, Murphy ME, Wang Y, Mason AB, Woodworth RC, Brayer GD, Baker EN | display-authors = 6 | title = Two high-resolution crystal structures of the recombinant N-lobe of human transferrin reveal a structural change implicated in iron release | journal = Biochemistry | volume = 37 | issue = 22 | pages = 7919–28 | date = June 1998 | pmid = 9609685 | doi = 10.1021/bi980355j }}</ref><ref name="Dewan_1993">{{cite journal | vauthors = Dewan JC, Mikami B, Hirose M, Sacchettini JC | title = Structural evidence for a pH-sensitive dilysine trigger in the hen ovotransferrin N-lobe: implications for transferrin iron release | journal = Biochemistry | volume = 32 | issue = 45 | pages = 11963–8 | date = November 1993 | pmid = 8218271 | doi = 10.1021/bi00096a004 }}</ref> Some invertebrates have proteins that act like transferrin found in the [[hemolymph]].<ref name="MacGillivray_1998" /><ref name="Baker_1992">{{cite journal | vauthors = Baker EN, Lindley PF | title = New perspectives on the structure and function of transferrins | journal = Journal of Inorganic Biochemistry | volume = 47 | issue = 3–4 | pages = 147–60 | date = August 1992 | pmid = 1431877 | doi = 10.1016/0162-0134(92)84061-q }}</ref>

When not bound to iron, transferrin is known as "apotransferrin" (see also [[Apoenzyme#Cofactors|apoprotein]]).