The link between vitamin B12 and methylmercury : a review : review article

The mercuric ion (Hg²⁺) is methylated in the sediment of aquatic systems to give methylmercury (CH₃Hg⁺), which is bioaccumulated in fish and has high toxicity for humans. Methylcobalamin, the methyl derivative of vitamin B₁₂ and a coenzyme in enzymatic methyl transfer, is able to methylate mercury(II). In the chemical reaction, the mercuric ion acts as an electrophile towards methylcobalamin in aqueous solution, giving aquocobalamin and methylmercury. It has been shown that sulphate-reducing bacteria, Desulphovibrio desulfuricans, methylate mercury(II) in aquatic sediments and that they use methylcobalamin to methylate mercuric ion. The methylation of mercury may be promoted by a synergistic interaction between sulphate-reducing bacteria and methanogens.