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出典(authority):フリー百科事典『ウィキペディア（Wikipedia）』「2016/06/12 15:48:37」(JST)

Transcobalamins are carrier proteins which bind cobalamin (B₁₂).

Transcobalamin I (TCN1), also known as haptocorrin, R-factor, and R-protein, is a glycoprotein produced by the salivary glands of the mouth. It primarily serves to protect cobalamin (Vitamin B12) from acid degradation in the stomach by producing a Haptocorrin-Vitamin B12 complex. Once the complex has traveled to the more neutral duodenum, pancreatic proteases degrade haptocorrin, releasing free cobalamin, which now binds to intrinsic factor for absorption by ileal enterocytes.
Transcobalamin II (TCN2) binds cobalamin once it has been uptaken by enterocytes of the terminal ileum and the "Intrinsic Factor-Vitamin B12" complex has been degraded. The TCII-Vit B12 complex then enters portal circulation and is processed in the liver.

Transcobalamins at the US National Library of Medicine Medical Subject Headings (MeSH)

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2. ビタミンB12および葉酸欠乏症の病因および臨床症状 etiology and clinical manifestations of vitamin b12 and folate deficiency
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4. 好中球二次顆粒欠損症 neutrophil specific granule deficiency

Mapping the functional domains of TCblR/CD320, the receptor for cellular uptake of transcobalamin-bound cobalamin.

Jiang W, Nakayama Y, Sequeira JM, Quadros EV.Source2Box 20, SUNY Downstate Medical Center, 450 Clarkson Ave., Brooklyn, NY 11203, USA. edward.quadros@downstate.edu.
FASEB journal : official publication of the Federation of American Societies for Experimental Biology.FASEB J.2013 Aug;27(8):2988-94. doi: 10.1096/fj.13-230185. Epub 2013 Apr 19.
The membrane receptor TCblR/CD320 binds transcobalamin (TC) saturated with vitamin B12 [cobalamin (Cbl)] and mediates cellular uptake of the vitamin. The specificity of TC for Cbl and of the receptor for TC-Cbl ensures efficient uptake of Cbl into cells. The high-affinity interaction of TCblR with T
PMID 23603833

Structural Basis for Universal Corrinoid Recognition by the Cobalamin Transport Protein Haptocorrin.

Furger E, Frei DC, Schibli R, Fischer E, Prota AE.SourcePaul Scherrer Institut, Switzerland.
The Journal of biological chemistry.J Biol Chem.2013 Jul 11. [Epub ahead of print]
Cobalamin (Cbl, vitamin B12) is an essential micronutrient only synthesized by bacteria. Mammals have developed a sophisticated uptake system to capture the vitamin from the diet. Cbl transport is mediated by three transport proteins: Transcobalamin (TC), intrinsic factor (IF) and haptocorrin (HC).
PMID 23846701

Metformin lowers serum cobalamin without changing other markers of cobalamin status: a study on women with polycystic ovary syndrome.

Greibe E, Trolle B, Bor MV, Lauszus FF, Nexo E.SourceDepartment of Clinical Biochemistry, Aarhus University Hospital, Norrebrogade 44, 8000 Aarhus C, Brendstrupgaardsvej 100, 8200 Aarhus N, Denmark. evagreibe@gmail.com
Nutrients.Nutrients.2013 Jul 5;5(7):2475-82. doi: 10.3390/nu5072475.
Treatment with the anti-diabetic drug metformin is followed by a decline in plasma cobalamin, but it is unsettled whether this denotes an impaired cobalamin status. This study has explored changes in the markers of cobalamin status in women with Polycystic Ovary Syndrome treated with metformin (1.5-
PMID 23857221

Hypercobalaminemia Induced by an Energy Drink after Total Gastrectomy : A Case Report

TC II deficiency : avoidance of false-negative molecular genetics by RNA-based investigations

transcobalamin II; macrocytic anemia
Identifiers
Symbol	TCN2
Entrez	6948
HUGO	11653
OMIM	275350
RefSeq	NM_000355
UniProt	P20062
Other data
Locus	Chr. 22 q11.2-qter

transcobalamin I (vitamin B12 binding protein, R binder family)
Identifiers
Symbol	TCN1
Entrez	6947
HUGO	11652
OMIM	189905
RefSeq	NM_001062
UniProt	P20061
Other data
Locus	Chr. 11 q11-q12