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transcobalamin I (vitamin B12 binding protein, R binder family)
Symbol TCN1
Entrez 6947
HUGO 11652
OMIM 189905
RefSeq NM_001062
UniProt P20061
Other data
Locus Chr. 11 q11-q12
transcobalamin II; macrocytic anemia
Symbol TCN2
Entrez 6948
HUGO 11653
OMIM 275350
RefSeq NM_000355
UniProt P20062
Other data
Locus Chr. 22 q11.2-qter

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 taken up by enterocytes of the terminal ileum and the "Intrinsic Factor-Vitamin B12" complex has been degraded. The TCII-Vit B12 complex then is processed in the liver.

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