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Vitamin B 12 is absorbed by a B 12-specific transport proteins or via passive diffusion. [12] Transport-mediated absorption and tissue delivery is a complex process involving three transport proteins: haptocorrin (HC), intrinsic factor (IF) and transcobalamin II (TC2), and respective membrane receptor proteins. HC is present in saliva.
TC-2 binds cobalamin once it has been taken up by enterocytes of the terminal ileum and the "Intrinsic Factor-Vitamin B12" complex has been degraded. TC-2 is then involved with the transport of Vitamin B12 to the tissues, where it binds to its plasma membrane receptor (TC-2R), a heavily glycosylated protein with a monomeric molecular mass of 62 ...
Because vitamin B 12 absorption is a multistep process that involves the stomach, pancreas and small intestine, and is mediated by two carriers: Haptocorrin and intrinsic factor, and because Haptocorrin (transcobalamin I) binds to vitamin B 12, and Vitamin B 12 is acid-sensitive, when vitamin B 12 binds to Haptocorrin it can safely pass through ...
That includes folks with an autoimmune disorder called pernicious anemia, who are unable to absorb B12, and people who take a lot of over-the-counter stomach-acid reducers, like famotidine ...
The same cells in the stomach that produce gastric hydrochloric acid, the parietal cells, also produce a molecule called the intrinsic factor (IF), which binds the B 12 after its release from haptocorrin by digestion, and without which only 1% of vitamin B 12 is absorbed. Intrinsic factor (IF) is a glycoprotein, with a molecular weight of 45 kDa.
In molecular biology, the vitamin B12-binding domain is a protein domain which binds to cobalamin (vitamin B12). It can bind two different forms of the cobalamin cofactor, with cobalt bonded either to a methyl group (methylcobalamin) or to 5'-deoxyadenosine (adenosylcobalamin).
Aerobic pathway that requires oxygen and in which cobalt is inserted late in the pathway; [6] [7] found in Pseudomonas denitrificans and Rhodobacter capsulatus.; Anaerobic pathway in which cobalt insertion is the first committed step towards cobalamin synthesis; [8] [9] [10] found in Salmonella typhimurium, Bacillus megaterium, and Propionibacterium freudenreichii subsp. shermanii.
Because they are soluble in water, excess B vitamins are generally readily excreted, although individual absorption, use and metabolism may vary. [7] The elderly and athletes may need to supplement their intake of B 12 and other B vitamins due to problems in absorption and increased needs for energy production.