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vitamin B12; cobalamin

Vitamin B12 assumes 3 biological forms, & a pharmaceutical form. 1) hydroxycobalamin 2) methylcobalamin 3) adenosylcobalamin 4) cyanocobalamin (pharmaceutical form) Co+2-containing cofactor in methyltransferase reactions including: 1) methylation of homocysteine*, in association with folic acid (enzyme: methionine synthase; cofactor: methylcobalamin) 2) metabolism of propionate (propionyl CoA) formed from catabolism of odd chain fatty acids, cholesterol & the amino acids methionine, valine & isoleucine (enzyme: methylmalonyl CoA mutase; cofactor: adenosylcobalamin) These are the only known functions of vitamin B12 in mammals [6]. * Also through this mechanism, plays a role in DNA synthesis Absorption of vitamin B12: Cobalamin is absorbed in association with intrinsic factor, a protein secreted by parietal cells in the gastric fundus. However, it is transcobalamin-1 that binds to vit B12 in the acidic environment of the stomach. Gastric acid facilitates release of cobalamin from binding in food sources. In the duodenum, transcobalamin-1 releases B12 for binding to intrinsic factor. The intrinsic factor/B12 complex is absorbed by attachment to specific receptors in the mucosal brush border of the ileum, i.e. cubilin. Amnionless is also necessary for efficient absorption of vitamin B12. About 1% of an oral dose of vitamin B12 is absorbed by passive diffusion. [7] Within the ileal mucosa, the intrinsic factor is metabolized & cobalamin is transferred to transcobalamin-2. The transcobalamin-2/B12 complex is secreted into the portal circulation from which about 1/2 is taken up by the liver. Most circulating vitamin B12 is bound to transcobalamin-1. However, it is probably metabolically inert since no cellular receptors for it have been identified. [10] In plasma, transcobalamin-2/vit B12 (holo-TC2) is the metabolically active form of vit B12. 6-20% of plasma TC2 is saturated with vit B12. Elimination 1/2life of the holo-TC2 in plasma is 1 hour. [3] Most of the peripheral holo-TC2 clearance occurs via glomerular filtration followed by tubular uptake in the kidney. Tubular epithelium is abundant in TC2 receptors [4] Liver stores of vitamin B12 are generally 2-5 mg. [9] Other proteins that partipate in vitamin B12 metabolism include: - MMACHC Dietary sources include: 1) meat 2) dairy products 3) vegetable products a) fermented soy b) yeast c) sea vegetables Recommended daily allowance (adults) - 2.4 ug; 2.6 ug if pregnant; 2.8 ug if lactating [13] See cyanocobalamin for pharmaceutical form of vitamin B12.

Related

Co+2 cubilin (intrinsic factor-cobalamin receptor, intrinsic factor-vitamin B12 receptor, 460 kD receptor, intestinal intrinsic factor receptor, CUBN, IFCR) intrinsic factor; gastric intrinsic factor; IF; INF (GIF, IFMH) methionine synthase; 5-methyltetrahydrofolate:homocysteine methyltransferase; vitamin-B12 dependent methionine synthase; tetrahydropteroyl-glutamate methyltransferase; MS (MTR) methylcobalamin deficiency methylmalonate; methylmalonic acid (MMA) methylmalonyl Coenzyme A mutase; succinyl CoA mutase; methylmalonyl CoA isomerase (MUT, MCM) Schilling test transcobalamin vitamin B12 deficiency vitamin B12 in serum/plasma

Specific

adenosylcobalamin; cobamamide (vitamin B12) cyanocobalamin (vitamin B12, Betalin-12, Redisol, Rubramin-PC) hydroxycobalamin (vitamin B12) methylcobalamin (vitamin B12)

General

benzimidazole B vitamin corrin

Properties

Database Correlations

PUBCHEM correlations

References

  1. Saunders Manual of Medical Practice, Rakel (ed), WB Saunders, Philadelphia, 1996, pg 1017
  2. Mayo Internal Medicine Board Review, 1998-99, Prakash UBS (ed) Lippincott-Raven, Philadelphia, 1998, pg 411
  3. Drug Information & Medication Formulary, Veterans Affairs, Central California Health Care System, 1st ed., Ravnan et al eds, 1998
  4. Kaiser Permanente Northern California Regional Drug Formulary, 1998
  5. UCLA Intensive Course in Geriatric Medicine & Board Review, Marina Del Ray, CA, Sept 12-15, 2001
  6. Stryer Biochemistry WH Freeman & Co, New York, 1988 pg 508
  7. Prescriber's Letter 8(10):55 2001
  8. Harrison's Online, Chapter 107, McGraw Hill, 2002
  9. Geriatrics Review Syllabus, American Geriatrics Society, 5th edition, 2002-2004 - Geriatric Review Syllabus, 9th edition (GRS9) Medinal-Walpole A, Pacala JT, Porter JF (eds) American Geriatrics Society, 2016
  10. Carmel R, Clinical Chemistry. 48:407-409. 2002 PMID: 11861432 http://www.clinchem.org/cgi/content/full/48/3/407
  11. O'Leary F, Samman S. Vitamin B12 in health and disease. Nutrients. 2010 Mar;2(3):299-316. Review. PMID: 22254022 Free PMC Article
  12. Malouf R, Areosa Sastre A. Vitamin B12 for cognition. Cochrane Database Syst Rev. 2003;(3):CD004326. Review. PMID: 12918012
  13. Khardori R Fast Five Quiz: Vitamin B12 Deficiency Medscape. December 22, 2020 https://reference.medscape.com/viewarticle/942750

Component-of

adenosylcobalamin/cobalamin alpha tocopherol/ascorbate/beta carotene/calcium carbonate/cholecalciferol/cobalamin/docosahexaenoate/folic acid/magnesium oxide/nicotinamide/pyridoxine/riboflavin/thiamine/zinc oxide alpha tocopherol/ascorbate/beta carotene/calcium carbonate/cholecalciferol/cobalamin/ferrous fumarate/folic acid/nicotinamide/pantothenate/pyridoxine/riboflavin/sodium docusate/thiamine/zinc oxide alpha tocopherol/ascorbate/beta carotene/calcium carbonate/cholecalciferol/cobalamin/folic acid/magnesium oxide/nicotinamide/pyridoxine/riboflavin/thiamine/zinc oxide alpha tocopherol/ascorbate/biotin/biotin/cobalamin/ergocalciferol/folic acid/multivitamin/nicotinamide/panthenol/pyridoxine/riboflavin/thiamine/vitamin a/vitamin k alpha tocopherol/ascorbate/biotin/cholecalciferol/cobalamin/folic acid/nicotinamide/panthenol/pyridoxine/riboflavin/thiamine/vitamin a/vitamin k alpha tocopherol/ascorbate/calcium carbonate/carbonyl iron/cholecalciferol/cobalamin/cupric oxide/folic acid/magnesium oxide/nicotinamide/pyridoxine/riboflavin/sodium docusate/thiamine/zinc oxide alpha tocopherol/ascorbate/carbonyl iron/cholecalciferol/cobalamin/folic acid/nicotinamide/pyridoxine/riboflavin/thiamine alpha tocopheryl acetate/ascorbate/beta carotene/cobalamin/ergocalciferol/folic acid/nicotinic acid/pantothenate/pyridoxine/retinol/riboflavin/thiamine alpha tocopheryl acetate/ascorbate/biotin/carbonyl iron/cobalamin/copper sulfate/folic acid/sodium docusate alpha tocopheryl acetate/ascorbate/biotin/carbonyl iron/cobalamin/folic acid/sodium docusate alpha tocopheryl acetate/ascorbate/calcium carbonate/cobalamin/copper sulfate/ferrous fumarate/folic acid/magnesium oxide/nicotinamide/potassium iodide/pyridoxine/retinol/riboflavin/thiamine/vitamin d/zinc sulfate alpha tocopheryl acetate/ascorbate/cholecalciferol/cobalamin/nicotinamide/pyridoxine/riboflavin/thiamine/vitamin a ascorbate/beta carotene/calcium carbonate/carbonyl iron/cholecalciferol/cobalamin/folic acid/magnesium oxide/nicotinamide/pyridoxine/riboflavin/sodium docusate/thiamine/zinc oxide ascorbate/bioflavonoid/choline bitartrate/cobalamin/inositol/nicotinamide/pantothenate/pyridoxine/riboflavin/thiamine ascorbate/biotin/calcium carbonate/cobalamin/dextran/folic acid/iron dextran/nicotinic acid/pantothenate/pyridoxine/riboflavin/thiamine ascorbate/biotin/calcium carbonate/cobalamin/ferrous fumarate/folic acid/magnesium oxide/nicotinamide/pantothenate/pyridoxine/riboflavin/thiamine/vitamin a/vitamin e/zinc oxide ascorbate/biotin/calcium carbonate/cobalamin/ferrous fumarate/folic acid/magnesium oxide/nicotinamide/pantothenate/pyridoxine/riboflavin/thiamine/vitamin a/vitamin e/zinc/zinc oxide ascorbate/biotin/cholecalciferol/cobalamin/folic acid/nicotinic acid/pantothenate/pyridoxine/riboflavin/thiamine ascorbate/biotin/cobalamin/copper sulfate/ferrous fumarate/folic acid/magnesium sulfate/manganese sulfate/nicotinic acid/pantothenate/polysaccharide iron complex/pyridoxine/riboflavin/thiamine/zinc sulfate ascorbate/biotin/cobalamin/folic acid/nicotinamide/pantothenate/pyridoxine/riboflavin/thiamine ascorbate/biotin/cobalamin/folic acid/nicotinic acid/pantothenate/pyridoxine/riboflavin/thiamine ascorbate/ca+2/cobalamin/folic acid/iron/polysaccharide iron complex ascorbate/calcium carbonate/cholecalciferol/choline bitartrate/cobalamin/docosahexaenoate/eicosapentaenoate/ferrous fumarate/folic acid/nicotinic acid/potassium iodide/pyridoxine/riboflavin/thiamine/vitamin e/zinc oxide ascorbate/carbonyl iron/cobalamin/folic acid ascorbate/carbonyl iron/cobalamin/folic acid/sodium docusate ascorbate/cholecalciferol/cobalamin/copper sulfate/ferrous fumarate/folic acid/kelp/magnesium oxide/magnesium sulfate/nicotinamide/pyridoxine/riboflavin/vitamin a/zinc sulfate ascorbate/cholecalciferol/cobalamin/folic acid/magnesium oxide/nicotinic acid/polysaccharide iron complex/potassium iodide/pyridoxine/riboflavin/thiamine/vitamin a/vitamin e/zinc oxide ascorbate/cholecalciferol/cobalamin/nicotinic acid/pyridoxine/riboflavin/sodium fluoride/thiamine/vitamin a/vitamin e ascorbate/cobalamin/copper sulfate/ferrous fumarate/folic acid/magnesium sulfate/manganese sulfate/nicotinamide/pantothenate/polysaccharide iron complex/pyridoxine/riboflavin/thiamine/zinc sulfate ascorbate/cobalamin/copper sulfate/ferrous fumarate/folic acid/magnesium sulfate/manganese sulfate/nicotinamide/pantothenate/pyridoxine/riboflavin/thiamine/zinc sulfate ascorbate/cobalamin/copper sulfate/ferrous fumarate/folic acid/manganese sulfate/nicotinamide/pantothenate/polysaccharide iron complex/pyridoxine/riboflavin/thiamine/zinc sulfate ascorbate/cobalamin/copper/copper sulfate/ferrous fumarate/folic acid/magnesium sulfate/manganese/manganese sulfate/nicotinamide/pantothenate/pyridoxine/riboflavin/thiamine/zinc sulfate ascorbate/cobalamin/ferrous fumarate ascorbate/cobalamin/ferrous fumarate/folic acid ascorbate/cobalamin/ferrous fumarate/folic acid/liver stomach concentrate ascorbate/cobalamin/folic acid ascorbate/cobalamin/folic acid/iron carbonyl/sodium docusate ascorbate/cobalamin/folic acid/nicotinic acid/pyridoxine/riboflavin/sodium fluoride/thiamine/vitamin a/vitamin d/vitamin e ascorbate/cobalamin/folic acid/sodium docusate ascorbate/cobalamin/nicotinic acid/pyridoxine/riboflavin/thiamine/vitamin a/vitamin d/vitamin e butafosfan/cobalamin caffeine/cobalamin/ibuprofen/pyridoxine/riboflavin/thiamine calcium ascorbate/calcium threonate/cobalamin/ferrous asparto glycinate/ferrous fumarate/folic acid/succinate calcium ascorbate/calcium threonate/cobalamin/ferrous asparto glycinate/liver stomach concentrate/succinate calcium carbonate/cobalamin/folic acid/pyridoxine cholecalciferol/cobalamin/fatty acid omega 3/folic acid/phytosterol/pyridoxine cholecalciferol/cobalamin/folic acid/pyridoxine/riboflavin cobalamin/docosahexaenoate/eicosapentaenoate/folic acid/phytosterol/policosanol/pyridoxine cobalamin/docosahexaenoate/eicosapentaenoate/folic acid/phytosterol/pyridoxine cobalamin/docosahexaenoate/eicosapentaenoate/pyridoxine cobalamin/fatty acid omega 3/folic acid/phytosterol/pyridoxine cobalamin/folic acid cobalamin/folic acid/heme/heme iron polypeptide/polypeptide/polysaccharide iron complex cobalamin/folic acid/heme/heme iron polypeptide/polysaccharide/polysaccharide iron complex cobalamin/folic acid/iron/polysaccharide iron complex cobalamin/folic acid/polysaccharide iron complex cobalamin/folic acid/pyridoxine cobalamin/magnesium sulfate/manganese sulfate/nicotinamide/panthenol/pyridoxine/riboflavin/thiamine/zinc sulfate cobalamin/magnesium sulfate/manganese/manganese sulfate/nicotinamide/panthenol/pyridoxine/riboflavin/thiamine/zinc sulfate cobalamin/nicotinamide/panthenol/pyridoxine/riboflavin/thiamine cobalamin/pyridoxine/riboflavin cobalamin/pyridoxine/thiamine cobalamin/thiamine Souvenaid; Fortasyn Connect