Transcobalamin

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

transcobalamin II; macrocytic anemia
Identifiers
Symbol	TCN2
Entrez	6948
HUGO	11653
OMIM	275350
PDB	2BB5
RefSeq	NM_000355
UniProt	P20062
Other data
Locus	Chr. 22 q11.2-qter

Transcobalamins are carrier proteins which bind cobalamin (B₁₂).

Types

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)

Proteins: carrier proteins
Fatty acid	FABP1 FABP2 FABP3 FABP4 FABP5 FABP6 FABP7
Hormone	peptide hormone: Follistatin Growth hormone binding protein Insulin-like growth factor binding protein IGFBP1 IGFBP2 IGFBP3 IGFBP4 IGFBP5 IGFBP6 IGFBP7 Neurophysins Neurophysin I II steroid hormone: Sex hormone binding globulin/Androgen binding protein Transcortin Thyroxine-binding globulin Transthyretin
Metal/element	calcium Calcium-binding protein Calmodulin-binding proteins copper Ceruloplasmin iron Iron-binding proteins Transferrin receptor
Vitamin	Retinol binding protein 1 2 3 4 Transcobalamin
Pigment	Plant Light-Harvesting Complex Orange Carotenoid Protein Phycobiliprotein Photosynthetic Reaction Centers Phytochrome Rhodopsin
Other	Acyl carrier protein Adaptor protein Cholesterylester transfer protein F-box protein GTP-binding protein Latent TGF-beta binding protein Major urinary proteins Membrane transport protein Odorant binding protein

serpins:	alpha-1 (Alpha 1-antichymotrypsin, Alpha 1-antitrypsin) alpha-2 (Alpha 2-antiplasmin) Antithrombin (Heparin cofactor II)
carrier proteins:	alpha-1 (Transcortin) alpha-2 (Ceruloplasmin) Retinol binding protein
other:	alpha-1 (Orosomucoid) alpha-2 (alpha-2-Macroglobulin, Haptoglobin)

carrier proteins:	Sex hormone-binding globulin Transferrin
other:	Angiostatin Hemopexin Beta-2 microglobulin Factor H Plasminogen Properdin

Other

Other globulins

Egg white	Conalbumin Ovalbumin Avidin
Serum albumin	Human serum albumin Bovine serum albumin Prealbumin
Other	C-reactive protein Lactalbumin (Alpha-lactalbumin) Parvalbumin Ricin

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