Transcobalamin

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transcobalamin I (vitamin B12 binding protein, R binder family)
Identifiers
SymbolTCN1
Chr. 11 q11-q12
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StructuresSwiss-model
DomainsInterPro
transcobalamin II; macrocytic anemia
Identifiers
SymbolTCN2
Chr. 22 q11.2-qter
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StructuresSwiss-model
DomainsInterPro

Transcobalamins are

cobalamin
(B12).

Types

Transcobalamin I (TCN1), also known as

cobalamin (Vitamin B12) from acid degradation in the stomach by producing a HC-Vitamin B12 complex. Once the complex has traveled to the more pH-neutral duodenum, pancreatic proteases degrade haptocorrin, releasing free cobalamin, which now binds to intrinsic factor
for absorption by ileal enterocytes.

Separate from the digestive absorption function, serum TCN1 binds 80-90% of circulating B12, rendering it unavailable for cellular delivery by TCN2.[1] Several serious, even life-threatening diseases cause elevated serum HC, measured as abnormally high serum vitamin B12.[2]

Transcobalamin II (TCN2), a nonglycoprotein secretory protein of molecular mass 43 kDa, binds cobalamin once it has been taken up by enterocytes of the terminal ileum and the "Intrinsic Factor-Vitamin B12" complex has been degraded. TCN2 is then involved with the transport of Vitamin B12 to the tissues, where it binds to its plasma membrane receptor (TCN2-R), a heavily glycosylated protein with a monomeric molecular mass of 62 kDa, and releases cobalamin to the cells.[3]

References

  1. PMID 36680553
    .
  2. PMID 14636871
    .
  3. PMID 10714245
    .

External links


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