Description
Vitamin B12 (cobalamin) is found free and also protein-bound in food.
The protein-bound form is degraded by pancreatic protease, releasing free B12 which binds to intrinsic factor, a protein secreted by gastric parietal cells of the stomach mucosa. The cobalamin intrinsic factor complex is bound to mucous membrane cells of the stomach in the ileum and absorbed by the cells. In the case of high doses, a diffusion of the complex also takes place. Vitamin B12 is bound to the protein transcobalamin II (TC-II) within the cells. TC-II serves as a transport protein for vitamin B12 in the circulation system. Vitamin B12 is involved as a coenzyme in metabolic processes and plays an important role in the formation of the blood, the development of the nervous system and the regeneration of the mucous membranes. In addition, there is a direct relationship to the formation of folic acid because methylcobalamin is involved in the transfer of methyl groups for the synthesis of methionine from homocysteine.
