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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.
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 ...
It primarily serves to protect cobalamin (Vitamin B12) from acid degradation in the stomach by producing a HC-Vitamin B 12 complex. Once the complex has traveled to the more pH-neutral duodenum, pancreatic proteases degrade haptocorrin, releasing free cobalamin, which now binds to intrinsic factor for absorption by ileal enterocytes.
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.
Vitamin B12 does also accumulate in a few plant-based sources, including some mushrooms, seaweed, and nutritional yeast, but not enough to fortify vegans, who, in particular, should consider being ...
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Vitamin B12 and bile salts are absorbed in the terminal ileum. Vitamin B12 will only be absorbed by the ileum after binding to a protein known as intrinsic factor. Water is absorbed by osmosis and lipids by passive diffusion throughout the small intestine. Sodium bicarbonate is absorbed by active transport and glucose and amino acid co-transport
The Good Housekeeping Institute tested more than 30 brands of B12 supplements, and chose Nature made B12 1000mcg as the best overall option, and Garden of Life Vitamin Code Raw B12 as the best ...