|File:Mecobalamin 3D sticks.png|
|Systematic (IUPAC) name|
|ATC code||B03BA05 (WHO)|
|Molecular mass||1344.40 g/mol|
|(what is this?)|
Methylcobalamin (mecobalamin, MeCbl, or MeB12) is a cobalamin, a form of vitamin B12. It differs from cyanocobalamin in that the cyanide 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, 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 not sufficient as a singular source of vitamin B12. Hydroxocobalamin and cyanocobalamin can both be split by the body into methylcobalamin and adenosylcoblamin. Methylcobalamin on the other hand is not converted into adenosylcobalamin. Deficiency of adenosylcobalamin disturbs carbohydrate, fat and amino-acid metabolism, and hence interferes with the formation of myelin. Thereby it is important to treat vitamin B12 deficiency with hydroxocobalamin or cyanocobalamin or a combination of adenosylcobalamin and methylcobalamin.
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.
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. In this role, methylcobalamin serves as a source of "CH3+".
A lack of methylcobalamin can lead to megaloblastic anemia and subacute combined degeneration of the spinal cord.
- L. R. McDowell, Vitamins in animal and human nutrition
- 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.
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