Methylcobalamin (Methyl-5,6-dimethylbenzimidazolylcobalamin, Methyl Vitamin B12, MeCb1) is the activated form of vitamin B12, and differs from vitamin B12 in that it contains a methyl group instead of a cyanide group. It functions as a coenzyme of methionine synthase which is essential for the conversion of homocysteine to methionine in the methylation cycle. Methylcobalamin has been used to treat some nutritional diseases and other diseases in clinic, such as Alzheimer's disease and rheumatoid arthritis. Recently several lines of evidence demonstrated that MeCbl may have potential analgesic effects in experimental and clinical studies.
Interrelationships between folic acid and cobalamin in the synthesis of methionine by extracts of Escherichia coli.
Vitamin B12-derivatives-enzyme cofactors and ligands of proteins and nucleic acids.
Methylcobalamin: a potential vitamin of pain killer.
 R.L.Kislink, et al, Biochem. J., 1960, 75(3), pp 467-477.