- Which one is required for vitamin B12 absorption in small intestine?
(1) Cobalophilin (2) Hephaestin
(3) Hepcidin (4) Na+-co-transporter
Vitamin B12 (cobalamin) absorption in the small intestine is a complex, multi-step process requiring specific proteins for proper uptake. Among these, Cobalophilin, also called R-protein or haptocorrin, plays an essential role in vitamin B12 absorption.
Mechanism of Vitamin B12 Absorption
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Release and Binding in Stomach: Vitamin B12 is initially bound to dietary proteins. In the stomach, gastric acid and proteases release B12 from these proteins. Free B12 then binds to cobalophilin (R-protein), a carrier protein secreted in saliva and the stomach.
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Protection and Transfer in Duodenum: The vitamin B12-cobalophilin complex travels to the duodenum, where pancreatic enzymes degrade cobalophilin, freeing B12.
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Binding to Intrinsic Factor: Free vitamin B12 then binds to intrinsic factor, a glycoprotein secreted by parietal cells of the stomach, forming the vitamin B12-intrinsic factor complex.
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Absorption in the Ileum: This complex moves to the distal ileum, where specific receptors on enterocytes recognize and mediate receptor-mediated endocytosis of the vitamin B12-intrinsic factor complex, facilitating absorption.
Explanation of Options
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Cobalophilin (Option 1): Critical for the initial binding and protection of vitamin B12 in the stomach and duodenum, facilitating its safe passage until intrinsic factor binding.
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Hephaestin (Option 2): Involved in iron metabolism, not related to vitamin B12 absorption.
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Hepcidin (Option 3): Regulates iron homeostasis; no role in vitamin B12 absorption.
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Na+-co-transporter (Option 4): Not involved in vitamin B12 absorption which instead depends on protein-mediated receptor endocytosis.
Conclusion
The correct protein required for vitamin B12 absorption in the small intestine among the options is:
(1) Cobalophilin
