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The receptor is specific to the IF-B 12 complex, and so will not bind to any vitamin content that is not bound to IF. [12] [121] Investigations into the intestinal absorption of B 12 confirm that the upper limit of absorption per single oral dose is about 1.5 μg, with 50% efficiency.
This complex then travels through the small bowel and reaches the terminal tertiary portion of the small intestine, called the ileum. The ileum is the longest of all portions of the small intestine, and has on its surface specialized receptors called cubilin receptors, that identify the B 12 –IF complexes and take them up into the circulation ...
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.
Vitamin B12 is an essential water-soluble vitamin, the absorption of which relies on a functional secretion of salivary haptocorrin, functional secretion of gastric intrinsic factor, functional cleavage of the haptocorrin via pancreatic protease, and a functional absorption via the Cubam at terminal ileum.
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 ...
These processes require the formation of the deoxyadenosyl radical through homolytic dissociation of the carbon-cobalt bond. This bond is exceptionally weak, with a bond dissociation energy of 31 kcal/mol, which is further lowered in the chemical environment of an enzyme active site . [ 2 ]
Vitamin B12 deficiency causes symptoms like fatigue, poor memory, a swollen tongue, and canker sores. Skip to main content. 24/7 Help. For premium support please call: 800-290-4726 more ways to ...
Enzymes that require adenosylcobalamin catalyse reactions in which the first step is the cleavage of adenosylcobalamin to form cob(II)alamin and the 5'-deoxyadenosyl radical, and thus act as radical generators. In both types of enzymes the B12-binding domain uses a histidine to bind the cobalt atom of cobalamin cofactors.
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