Methylcobalamin (mecobalamin, MeCbl, or MeB) is a

cobalamin Vitamin B12, also known as cobalamin, is a water-soluble vitamin involved in metabolism. It is one of eight B vitamins. It is required by animals, which use it as a cofactor in DNA synthesis, in both fatty acid and amino acid metabolism. ...

, 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. Though these vitamins share similar names (B1, B2, B3, etc.), they are chemically distinct compounds that often coex ...

. It differs from

cyanocobalamin Cyanocobalamin is a form of vitamin used to treat vitamin deficiency except in the presence of cyanide toxicity. The deficiency may occur in pernicious anemia, following surgical removal of the stomach, with fish tapeworm, or due to bowel ...

in that the

cyano group Cyanide is a naturally occurring, rapidly acting, toxic chemical that can exist in many different forms. In chemistry, a cyanide () is a chemical compound that contains a functional group. This group, known as the cyano group, consists of a ...

at the cobalt 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 . In formulas, the group is often abbreviated as Me. This hydrocarbon group occurs in ma ...

. Methylcobalamin features an octahedral cobalt(III) centre and can be obtained as bright red crystals. From the perspective of coordination chemistry, methylcobalamin is notable as a rare example of a compound that contains metal–alkyl bonds.

Nickel Nickel is a chemical element with 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 slow ...

–methyl intermediates have been proposed for the final step of methanogenesis. 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 also used in the treatment of

peripheral neuropathy Peripheral neuropathy, often shortened to neuropathy, is a general term describing disease affecting the peripheral nerves, meaning nerves beyond the brain and spinal cord. Damage to peripheral nerves may impair sensation, movement, gland, or or ...

, diabetic neuropathy, and as a preliminary treatment for amyotrophic lateral sclerosis. Methylcobalamin that is ingested is not used directly as a cofactor, but is first converted by

MMACHC Methylmalonic aciduria and homocystinuria type C protein (MMACHC) is a protein that in humans is encoded by the ''MMACHC'' gene. Function The C-terminal region of the product of the MMACHC gene is similar to TonB, a bacterial protein involved ...

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. According to one author, it is important to treat

deficiency with

hydroxocobalamin Hydroxocobalamin, also known as vitamin B12a and hydroxycobalamin, is a vitamin found in food and used as a dietary supplement. As a supplement it is used to treat vitamin B12 deficiency including pernicious anemia. Other uses include treatment ...

or a combination of

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

and methylcobalamin, and not methylcobalamin alone. __TOC__

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 Na BH4. This white solid, usually encountered as an aqueous basic solution, is a reducing agent that finds applica ...

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

Functions

This

vitamer Vitamins occur in a variety of related forms known as vitamers. A vitamer () of a particular vitamin is one of several related compounds that performs the functions of said vitamin and prevents the symptoms of deficiency of said vitamin. Early r ...

, along with

, 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 Methionine synthase also known as MS, MeSe, MTR is responsible for the regeneration of methionine from homocysteine. In humans it is encoded by the ''MTR'' gene (5-methyltetrahydrofolate-homocysteine methyltransferase). Methionine synthase forms ...

(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 Bacteria (; singular: bacterium) are ubiquitous, mostly free-living organisms often consisting of one Cell (biology), biological cell. They constitute a large domain (biology), domain of prokaryotic microorganisms. Typically a few micrometr ...

. It plays an important role in the environment. In the environment, it is responsible for the

biomethylation In the chemical sciences, methylation denotes 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 ...

of certain heavy metals. For example, the highly toxic methylmercury is produced by the action of methylcobalamin. In this role, methylcobalamin serves as a source of "CH₃⁺". A lack of cobalamin can lead to

megaloblastic anemia Megaloblastic anemia is a type of macrocytic anemia. An anemia is a red blood cell defect that can lead to an undersupply of oxygen. Megaloblastic anemia results from inhibition of DNA synthesis during red blood cell production. When DNA synth ...

and subacute combined degeneration of the spinal cord.

References

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

Production

Functions

See also

References