Transcobalamine

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The human transcobalamines , also called haptocorrins or R-binder proteins , are a group of transport proteins for vitamin B 12 ( cobalamin ). The active vitamin B12 bound to transcobalamin is called holotranscobalamin (Holo-TC).

There are currently three transcobalamins: Transcobalamin I, II and III.

Transcobalamin I is a 433 amino acid protein with a molecular mass of 48,209 Daltons , which is encoded on chromosome 11 and migrates as beta globulin during electrophoresis. Transcobalamin I is used to transport excess vitamin B 12 in the blood back to the liver as its storage organ .

Transcobalamin II is a 427 amino acid protein with a molecular mass of 47,538 Daltons, which is encoded on chromosome 22 and migrates as alpha globulin during electrophoresis (like transcobalamin III). Transcobalamin II is used to transport vitamin B 12 to the cells that take up the vitamin B 12 transcobalamin complex (also called holo-transcobalamin II or holo-TC II ) by binding to a membrane receptor (so-called "receptor-mediated endocytosis ") can.

In detail, holo-transcobalamin II is absorbed via a special transcobalamin II receptor, which, together with the vitamin B 12 transcobalamin complex, migrates from the blood to the inside of the cell in a "coated vesicle", from where the transcobalamin II is transported back into the blood after the release of vitamin B 12 .

Genetic malformations are known for transcobalamin II ( chromosome 22q12.2 ) which, despite normal serum values, can lead to a cellular vitamin B 12 deficiency, and this in turn to a number of disorders that occur at birth such as anemia and immune deficiency due to Immunoglobulin G deficiency or various neurological symptoms.

literature

  • MeSH Transcobalamine National Library of Medicine - Medical Subject Headings: Transcobalamins.
  • L. Thomas: Laboratory and Diagnosis. 6th edition 2005.

Individual evidence

  1. www.endokrinologikum.com: Holotranscobalamin .
  2. Human Protein Reference Database
  3. Human Protein Reference Database
  4. ^ Li N. et al .: Identification of two mutant alleles of transcobalamin II in an affected family. Hum Mol Genet . (1994) 3 (10): 1835-40. PMID 7849710 .