Mercury is a highly toxic heavy metal (ToxFAQs: Mercury). Its toxicity can result from three different forms of it, elemental (Hg0), mercuric ion (Hg2+), or organic mercury compounds. It can be absorbed through respiratory tract, skin, or digestive tract, and give rise to poisoning. Mercury toxicity is related to its affinity to form tight coordinate bonds with sulfhydryl groups diffusely disrupting enzyme systems in multiple organs such as brain, kidney, and lung.
While mercury poisoning is still seen in some occupations, recently there has been much concern over the potential health hazards brought about by the contamination of many ecosystems. Different forms of mercury in the environment can be interconverted. Methylmercury may be formed in water and soil and accumulated in fish, which could cause mercury poisoning after ingestion.
Phenylmercuric acetate has been used as a pesticide, herbicide, fungicide, disinfectant and a preservative in cosmetics. Methylmercury chloride has been used as a fungicide. Some bacteria are resistant to inorganic mercury salts and organomercurials including the above two compounds because they contain two enzymes for mercury conversion. Organomercurial lyase cleaves the C-Hg bond and releases Hg(II) in addition to the respective organic compound (Begley et al., 1986). Mercuric reductase reduces Hg(II) to Hg0, which is less reactive and toxic, and easily volatilizes from the medium (Schiering et al., 1991). In the reactions shown in the graphical pathway map, thiolates act as ligands to the mercury. This reflects observations that cellular thiols act to coordinate mercury during biological mercury transport and are likely going on and coming off the surface of the enzymes organomercurial lyase and mercuric reductase, respectively.
The following is a text-format organomercury pathway map. Organisms which can initiate the pathway are given. Follow the links for more information on compounds or reactions. This map is also available in graphic (10k) format.
Methylmercury Phenylmercury chloride acetate Escherichia Pseudomonas coli J53-1 fluorescens | | | | | | | | | organomercurial | organomercurial | lyase | lyase / \ / \ / \ / \ / \ / \ / \ / \ v v v v Methane Hg2+ Benzene + Acetate | | | | | | | | | | mercuric | | | | reductase | | | | | | | | | | v v v v to the Hg0 to the Intermediary C1 Metabolic Beta-HCH Metabolism Cycle Pathway (KEGG)
Page Author(s): Aidas Nasevicius, Jun OuYang, Stephen Stephens, and Zhifu Sun
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