Methylcobalamin (mecobalamin, MeCbl, or MeB) is a

cobalamin Vitamin B12, also known as cobalamin, is a water-soluble vitamin involved in metabolism. One of eight B vitamins, it serves as a vital cofactor (biochemistry), cofactor in DNA synthesis and both fatty acid metabolism, fatty acid and amino a ...

, a form of vitamin B. It differs from

cyanocobalamin Cyanocobalamin is a form of Vitamin B12, vitamin used to treat and prevent vitamin B12 deficiency, vitamin deficiency except in the presence of cyanide toxicity. The deficiency may occur in pernicious anemia, following gastrectomy, surgical r ...

in that the cyano group at the cobalt is replaced with a methyl group. Methylcobalamin features an octahedral cobalt(III) centre and can be obtained as bright red crystals. From the perspective of

coordination chemistry A coordination complex is a chemical compound consisting of a central atom or ion, which is usually metallic and is called the ''coordination centre'', and a surrounding array of chemical bond, bound molecules or ions, that are in turn known as ' ...

, 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. __TOC__

Production

Methylcobalamin can be produced in the laboratory by reducing

with sodium borohydride in alkaline solution, followed by the addition of methyl iodide.

Functions

This vitamer, along with adenosylcobalamin, is one of two active coenzymes used by vitamin B-dependent enzymes and is the specific vitamin B 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. Methylcobalamin is produced by some bacteria. It plays an important role in the environment, where it is responsible for the biomethylation of certain heavy metals. For example, the highly toxic

methylmercury Methylmercury is an organometallic cation with the formula . It is the simplest organomercury compound. Methylmercury is extremely toxic, and its derivatives are the major source of organic mercury for humans. It is a bioaccumulative environment ...

is produced by the action of methylcobalamin. In this role, methylcobalamin serves as a source of "CH₃⁺".

Role in human health

Methylcobalamin is equivalent physiologically to vitamin B, and can be used to prevent or treat pathology arising from a lack of vitamin B intake ( vitamin B₁₂ deficiency). Methylcobalamin is considered to be equivalent in efficacy to the other vitamin B12 vitamers as a dietary supplement, with no clear evidence of differing efficacy between them. Methylcobalamin that is ingested is not used directly as a cofactor, but is first converted by MMACHC into cob(II)alamin. Cob(II)alamin is then later converted into the other two forms, adenosylcobalamin and methylcobalamin for use as cofactors. That is, methylcobalamin is first dealkylated and then regenerated.

Research directions

Ultra-high-dose intravenous methylcobalamin is researched as treatment of peripheral neuropathy, diabetic neuropathy, and as a preliminary treatment for

amyotrophic lateral sclerosis Amyotrophic lateral sclerosis (ALS), also known as motor neuron disease (MND) or—in the United States—Lou Gehrig's disease (LGD), is a rare, Terminal illness, terminal neurodegenerative disease, neurodegenerative disorder that results i ...

References

{{Enzyme cofactors B vitamins Cofactors Methylating agents Organocobalt compounds Vitamin B12

Production

Functions

Role in human health

Research directions

See also

References