The Role of Mercury Speciation in its Methylation by Methylcobalamin (vitamin-B12)

Abstract

Mono-methyl mercury (MMHg) travels through the food chain by means of bioaccumulation, and humans are exposed to this potent neurotoxin by consumption of contaminated fish and shellfish products. Although it is well established that certain sulfate-reducing bacteria (SRB) present in both freshwater and saline systems transform inorganic mercury into its mono-methyl counterpart as a metabolic by-product, the role of abiotic or chemical methylation remains unclear. One family of molecules that have been investigated with regard to abiotic methylation is the inorganic methylcobalt (III) complexes, namely methylcobalamin (MeCo), a derivative of vitamin-B12. MeCo has been implicated in the in vivo methylation of Hg in many SRB, but previous research has not established its significance for abiotic methylation, particularly in saline environments. In this research study, we conducted in vitro experiments to assess the ability of several Hg complexes to become methylated by B12. This research may provide a better understanding of the nature and importance of abiotic mercury methylation by methylcobalamin in sulfur-rich environments.