Intrinsic factor
| Intrinsic factor | ||
|---|---|---|
| Properties of human protein | ||
| Mass / length primary structure | approx. 50 kDa , 399 amino acids | |
| Identifier | ||
| Gene name | GIF | |
| External IDs | ||
| Occurrence | ||
| Parent taxon | Mammals | |
The intrinsic factor , also called intrinsic factor , abbreviated to IF , is the name of a glycoprotein in mammals and is used to absorb cobalamin (vitamin B 12 , extrinsic factor ) in the terminal ileum (hip intestine). Mutations in GIF - gene can IF deficiency, vitamin B 12 deficiency and pernicious anemia lead.
Physiological importance
Vitamin B 12 may be only in the terminal ileum, the lower part of the small intestine , reabsorbed be. Although it is produced in large quantities by the intestinal bacteria in the large intestine, it is behind the abovementioned absorption section. This means that the body's own vitamin cannot be used and must be taken in with food. The faeces of many animals, e.g. B. monkeys, may have this background.
Vitamin B 12 contains cobalamin in protein-bound form. The vitamin is broken down by proteolytic processes in the stomach of the digestive enzymes pepsin and trypsin . In order to be able to absorb cobalamin , the intrinsic factor formed in humans by the parietal cells of the gastric mucosa is necessary. It is a glycoprotein of around 50 kDa. It binds cobalamin, which can then be taken up in the terminal ileum via specific receptors.
The cobalamin intrinsic factor complex is split in the intestinal epithelial cells . Cobalamin is transported in the bloodstream by the transport protein Transcobalamin II.
Mode of action
In most mammals, the intrinsic factor is produced by the parietal cells of the stomach floor (fundus ventriculi) and body (corpus ventriculi). In cats , the intrinsic factor is formed exclusively in the pancreas , in dogs a considerable part.
The intrinsic factor cobalamin complex moves into the intestine, where it binds to cubilin on the outside of epithelial cells . After Megalin is also bound to cubilin, the entire complex is transported into the interior of the cell via endocytosis .
The absorption of cobalamin via the intrinsic factor is limited. Excess amounts ingested are largely excreted and small parts remain in the body through diffusion processes.
Diseases
In rare cases (approx. 1 case per 10,000 inhabitants per year), there may be a deficiency in the intrinsic factor. As a result, these people may develop pernicious anemia or funicular myelosis .
The reason for such a deficiency can e.g. B. the autoimmune disease A gastritis (chronic gastritis type A). Here the body attacks the intrinsic factor-producing parietal cells and destroys them. In dogs and cats, diseases of the pancreas lead to a deficiency. The absorption of vitamin B 12 is then severely restricted. As a rule, high-dose oral administration of vitamin B 12 (1 mg daily) is sufficient in such cases . Parenteral administration in the form of intramuscular administration (vitamin B 12 injection) is only required in exceptional cases.
With the help of the Schilling test (according to Robert F. Schilling , 1953) a distinction can be made between intrinsic factor deficiency and absorption deficits.
literature
- Robert F. Schilling: Intrinsic factor studies. II. The effect of gastric juice on the urinary excretion of radioactivity after the oral administration of radioactive vitamin B 12 . In: J. Lab. Clin. Med. 42, 1953, pp. 860-866.
Individual evidence
- ↑ Homology group at OMA
- ↑ UniProt P27352
- ↑ JC Fyle: Feline Intrinsic Factor (IF) is pancreatic in origin and mediates ileal cobalamin (CBL) absorption. In: J. Vet. Intern. Med. 7, 1993, pp. 133-135.