Methylcobalamin (mecobalamin, MeCbl, or MeB12) is a
cobalamin, a form of
vitamin B12. It differs from
cyanocobalamin in that the
cyano group at the cobalt is replaced with a
methyl group.[1] Methylcobalamin features an octahedral cobalt(III) centre and 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,[3] and can be used to prevent or treat pathology arising from a lack of vitamin B12 intake (
vitamin B12 deficiency).
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.[5][6][7]
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.[9]
Methylcobalamin is produced by some
bacteria.[citation needed] 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 is produced by the action of methylcobalamin.[10] In this role, methylcobalamin serves as a source of "CH3+".
A lack of cobalamin can lead to
megaloblastic anemia and subacute combined degeneration of the spinal cord.[11]
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abDavid D (January 1971). "Preparation of the Reduced Forms of Vitamin B12 and of Some Analogs of the Vitamin B12 Coenzyme Containing a Cobalt-Carbon Bond". In McCormick DB, Wright LD (eds.). Vitamins and Coenzymes. Methods in Enzymology. Vol. 18. Academic Press. pp. 34–54.
doi:
10.1016/S0076-6879(71)18006-8.
ISBN9780121818821.