Intrinsic factor

• OMIM: 609 342
• UniProt: P27352

The intrinsic factor (IF ) is a glycoprotein in mammals, and is used to hold cobalamin (vitamin B12, the extrinsic Factor) in the terminal ileum ( Hüftdarm ). Mutations in the GIF gene can cause IF deficiency, vitamin B12 deficiency and pernicious anemia.

Physiological significance

Vitamin B12 can be only in the terminal ileum, the lower part of the small intestine, absorbed. Although it is formed by the intestinal bacteria of the colon in large amounts, however, behind said Resorptionsabschnitt. This can not be utilized the body's own vitamin formed and must be taken with food. The Kotaufnahme of many animals, such as Monkeys, may have this background.

Vitamin B12 Cobalamin contains protein bound. Proteolytic processes in the stomach of the digestive enzymes pepsin and trypsin, the vitamin is decomposed. To record cobalamin, which formed in humans by the parietal cells of the gastric mucosa intrinsic factor is necessary. Is a glycoprotein of approximately 50 kDa. It binds cobalamin which can be added as in the terminal ileum via specific receptors. The cobalamin - intrinsic factor complex, is cleaved in the enterocytes. Cobalamin in the blood stream, transported by a transport protein transcobalamin II.

Operation

The intrinsic factor (ie the specific glycoprotein ) is produced in most mammals by the parietal cells of the stomach bottom ( fundus ulcer ) and body ( corpus ulcer ). In cats, the intrinsic factor is produced exclusively in the pancreas in dogs a significant part.

The intrinsic factor - cobalamin complex moves into the intestine where it binds to the outside of epithelial cells to cubilin. After also megalin is bound to cubilin, the total complex by endocytosis is transported into the cell.

Diseases

In rare cases ( about 9 cases per year per 100 000 population ) may lead to a lack of intrinsic factor. These people can, consequently, pernicious anemia or a funicular myelosis occur.

The reason for such a lack may be (chronic gastritis type A), for example, the Autoimmunkrankeit A- gastritis. Here, the body attacks the intrinsic factor -producing parietal cells and destroys them. In dogs and cats diseases of the pancreas leading to a deficiency. The absorption of vitamin B12 is then severely limited. As a rule, sufficient in such cases, the high -dose oral administration of vitamin B12 ( 1 mg daily) from. A parenteral administration in the form of intramuscular administration (vitamin B12 injection ) is only required in exceptional cases. For Healthy vitamin B12 supplements are useless, since most of it would excreted unused and the body's custodian holds enough cobalamin for 3-5 years.