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 B vitamins are a class of water-soluble vitamins that play important roles in cell metabolism and synthesis of red blood cells. They are a chemically diverse class of compounds. Dietary supplements containing all eight are referred to as a vita ...

. 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 Cobalt is a chemical element; it has Symbol (chemistry), symbol Co and atomic number 27. As with nickel, cobalt is found in the Earth's crust only in a chemically combined form, save for small deposits found in alloys of natural meteoric iron. ...

is replaced with a

methyl group In organic chemistry, a methyl group is an alkyl derived from methane, containing one carbon atom bonded to three hydrogen atoms, having chemical formula (whereas normal methane has the formula ). In formulas, the group is often abbreviated a ...

. 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 Nickel is a chemical element; it has symbol Ni and atomic number 28. It is a silvery-white lustrous metal with a slight golden tinge. Nickel is a hard and ductile transition metal. Pure nickel is chemically reactive, but large pieces are slo ...

–methyl intermediates have been proposed for the final step of

methanogenesis Methanogenesis or biomethanation is the formation of methane coupled to energy conservation by microbes known as methanogens. It is the fourth and final stage of anaerobic digestion. Organisms capable of producing methane for energy conservation h ...

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Production

Methylcobalamin can be produced in the laboratory by reducing

with

sodium borohydride Sodium borohydride, also known as sodium tetrahydridoborate and sodium tetrahydroborate, is an inorganic compound with the formula (sometimes written as ). It is a white crystalline solid, usually encountered as an aqueous basic solution. Sodi ...

in alkaline solution, followed by the addition of

methyl iodide Iodomethane, also called methyl iodide, and commonly abbreviated "MeI", is the chemical compound with the formula CH3I. It is a dense, colorless, volatile liquid. In terms of chemical structure, it is related to methane by replacement of one h ...

Functions

This

vitamer A vitamer () is any of the related forms in which some vitamin occurs. Each vitamer of a particular vitamin is a compound that performs the functions of that vitamin and prevents the symptoms of deficiency of the vitamin. Early research identifi ...

, along with

adenosylcobalamin Adenosylcobalamin (AdoCbl), also known as coenzyme B12, cobamamide, and dibencozide, is one of the biologically active forms of vitamin B12. Adenosylcobalamin participates as a cofactor in radical-mediated 1,2-carbon skeleton rearrangements. T ...

, 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 (acetyl coenzyme A) is a molecule that participates in many biochemical reactions in protein, carbohydrate and lipid metabolism. Its main function is to deliver the acetyl group to the citric acid cycle (Krebs cycle) to be oxidation, o ...

. 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 Methylation, in the chemical sciences, is the addition of a methyl group on a substrate, or the substitution of an atom (or group) by a methyl group. Methylation is a form of alkylation, with a methyl group replacing a hydrogen atom. These terms ...

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 Vitamins are organic molecules (or a set of closely related molecules called vitamers) that are essential to an organism in small quantities for proper metabolic function. Essential nutrients cannot be synthesized in the organism in suff ...

). Methylcobalamin is considered to be equivalent in efficacy to the other vitamin B12

s 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,

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 Peripheral neuropathy, often shortened to neuropathy, refers to damage or disease affecting the nerves. Damage to nerves may impair sensation, movement, gland function, and/or organ function depending on which nerve fibers are affected. Neuropa ...

diabetic neuropathy Diabetic neuropathy includes various types of nerve damage associated with diabetes mellitus. The most common form, diabetic peripheral neuropathy, affects 30% of all diabetic patients. Studies suggests that cutaneous nerve branches, such as the s ...

, 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