transcobalamin-2; TC-2; transcobalamin II; salivary factor TC II; TCII (TCN2, TC2)
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Function
- chief transport protein of methyl-cobalamin (vit B12) from ileum to the liver
- ~1/2 of the TC2/vit B12 complex (holo-TC2) is cleared by the liver
- in plasma, holo-TC2 is the metabolically active form of vit B12
- 6-20% of TC2 is saturated as holo-TC2
Structure
- belongs to the eukaryotic cobalamin transport proteins family
Compartment
Expression
- secreted by hepatocytes
- may be expressped by renal tubular epithelial cells
Pathology
- defects in TCN2 are the cause of transcobalamin II deficiency
Polymorphism
- Pro/Arg-259 polymorphism affects TCN2 plasma concentration & may interfere in vitamin B(12) cellular availability & homocysteine metabolism
Pharmacokinetics
- elimination 1/2life of the holo-TC2 in plasma is 1 hour.[3]
- most of the peripheral holo-TC2 clearance occurs via glomerular filtration followed by tubular uptake in the kidney
- renal tubular epithelium is abundant in TC2 receptors[4]
- animal studies suggest that renal tubules also synthesize TC2, which emerges in the blood stream as new holo-TC2 carrying the reabsorbed cobalamin[4]
- pathologic influences on most of these individual phases in the cycle are unknown
More general terms
References
- ↑ Clinical Diagnosis & Management by Laboratory Methods, J.B. Henry (ed), W.B. Saunders Co., Philadelphia, PA. 1991, pg 632
- ↑ Cotran et al Robbins Pathologic Basis of Disease, W.B. Saunders Co, Philadelphia, PA 1989 pg 456
- ↑ 3.0 3.1 Harrison's Online, Chapter 107, McGraw Hill, 2002
- ↑ 4.0 4.1 4.2 Carmel R Clinical Chemistry. 48:407-409. 2002
- ↑ UniProt http://www.uniprot.org/uniprot/P20062.html
- ↑ TCN2base; Note: TCN2 mutation db http://bioinf.uta.fi/TCN2base/