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Methylcobalamin (mecobalamin, MeCbl, or MeB₁₂) is a cobalamin, a form of vitamin B₁₂. It differs from cyanocobalamin in that the cyanide is replaced by a methyl group.^[1] Methylcobalamin features an octahedral cobalt(III) centre. Methylcobalamin can be obtained as bright red crystals.^[2] From the perspective of coordination chemistry, methylcobalamin is notable as a rare example of a compound that contains metal-alkyl bonds. Nickel-methyl intermediates have been proposed for the final step of methanogenesis.

Methylcobalamin is equivalent physiologically to vitamin B₁₂, and can be used to prevent or treat pathology arising from a lack of vitamin B₁₂ (vitamin B12 deficiency), such as pernicious anemia.

Methylcobalamin is also used in the treatment of peripheral neuropathy, diabetic neuropathy, and as a preliminary treatment for amyotrophic lateral sclerosis.

Production[edit source | edit]

Methylcobalamin physically resembles the other forms of vitamin B₁₂, occurring as dark red crystals that freely form cherry-colored transparent solutions in water.

Methylcobalamin can be produced in the laboratory by reducing cyanocobalamin with sodium borohydride in alkaline solution, followed by the addition of methyl iodide.^[2]

Functions[edit source | edit]

This vitamer is one of two active coenzymes used by vitamin B₁₂-dependent enzymes and is the specific vitamin B₁₂ form used by 5-methyltetrahydrofolate-homocysteine methyltransferase (MTR), also known as methionine synthase.

Methylcobalamin participates in the Wood-Ljungdahl pathway, which is a pathway by which some organisms utilize carbon dioxide as their source of organic compounds. In this pathway, methylcobalamin provides the methyl group that couples to carbon monoxide (derived from CO₂) to afford acetyl-CoA. Acetyl-CoA is a derivative of acetic acid that is converted to more complex molecules as required by the organism.^[3]

Methylcobalamin is produced by some bacteria. It plays an important role in the environment. In the environment, it is responsible for the biomethylation of certain heavy metals. For example, the highly toxic methylmercury is produced by the action of methylcobalamin.^[4] In this role, methylcobalamin serves as a source "CH₃⁺".

References[edit source | edit]

^ L. R. McDowell, Vitamins in animal and human nutrition
^ ^a ^b David Dophin. Preparation of the Reduced Forms of Vitamin B₁₂ and of Some Analogs of the Vitamin B₁₂ Coenzyme Containing a Cobalt-Carbon Bond. D.B. McCormick and L.D. Wright, Eds. 1971;Vol. XVIII:34-54.
^ 1. J. C. Fontecilla-Camps, P. Amara, C. Cavazza, Y. Nicolet and A. Volbeda, "Structure-function relationships of anaerobic gas-processing metalloenzymes", Nature 2009, volume 460, p. 814-822.doi:10.1038/nature08299
^ Zenon Schneider, Andrzej Stroiński, Comprehensive B12: Chemistry, Biochemistry, Nutrition, Ecology, Medicine

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UpToDate Contents

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English Journal

Treatment of vitamin B12 deficiency-Methylcobalamine? Cyancobalamine? Hydroxocobalamin?-clearing the confusion.

Thakkar K1, Billa G2.
European journal of clinical nutrition.Eur J Clin Nutr.2014 Aug 13. doi: 10.1038/ejcn.2014.165. [Epub ahead of print]
Vitamin B12 (cyancobalamin, Cbl) has two active co-enzyme forms, methylcobalamin (MeCbl) and adenosylcobalamin (AdCbl). There has been a paradigm shift in the treatment of vitamin B12 deficiency such that MeCbl is being extensively used and promoted. This is despite the fact that both MeCbl and AdCb
PMID 25117994

Meta-analysis of methylcobalamin alone and in combination with prostaglandin E1 in the treatment of diabetic peripheral neuropathy.

Deng H1, Yin J, Zhang J, Xu Q, Liu X, Liu L, Wu Z, Ji A.
Endocrine.Endocrine.2014 Aug;46(3):445-54. doi: 10.1007/s12020-014-0181-6. Epub 2014 Feb 13.
This study aimed to compare the efficacy and safety of prostaglandin E1 plus methylcobalamin (PGE1-MC) with that of methylcobalamin alone (MC) on diabetic peripheral neuropathy (DPN). We searched published randomized controlled trials (RCTs) of PGE1 combined with MC for DPN up to June 1, 2013. Data
PMID 24522613

Unexpected recovery of moderate cognitive impairment on treatment with oral methylcobalamin.

Rietsema WJ.
Journal of the American Geriatrics Society.J Am Geriatr Soc.2014 Aug;62(8):1611-2. doi: 10.1111/jgs.12966.
PMID 25116994

Japanese Journal

古くて新しいビタミンB₁₂と末梢神経障害

田中啓之
Brain and nerve : 神経研究の進歩 65(9), 1077-1082, 2013-09
NAID 40019803695

筋におけるメチルコバラミンの影響

岡本道雄
末梢神経 = Peripheral nerve 22(2), 361-362, 2011-12-01
NAID 10030408725

p70 ribosomal S6 protein kinase の活性化と methylcobalamin 作用機序の関係

岡田潔,田中啓之,轉法輪光,黒田有佑,岡本道雄,森友寿夫,村瀬剛,名井陽,吉川秀樹
末梢神経 = Peripheral nerve 22(2), 309-310, 2011-12-01
NAID 10030408595

「メチルコバラミン」

Methylcobalamin
Systematic (IUPAC) name
	carbanide; cobalt(3+);
Clinical data
AHFS/Drugs.com	International Drug Names
Pregnancy cat.	?
Legal status	OTC (US)
Routes	oral,sublingual,injection.
Identifiers
CAS number	13422-55-4
ATC code	B03BA05
PubChem	CID 6436232
UNII	BR1SN1JS2W
ChEMBL	CHEMBL1697757
Chemical data
Formula	C63H91CoN13O14P
Mol. mass	1344.40 g/mol
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