Fig. 2.
Transformation of mercury species in mammalian tissues. Mercuric ions that are ingested, absorbed or inhaled may bond with glutathione (GSH) and/or cysteine (Cys) to form G-S- and Cys-S-conjugates of Hg2+ (G-S-Hg-S-G, Cys-S-Hg-S-Cys, respectively) and methylmercury (CH3Hg-S-G, CH3Hg-S-Cys, respectively). G-S-Hg-S-G and CH3Hg-S-G are processed further by γ-glutamyltransferase and cysteinylglycinase to yield Cys-S-Hg-S-Cys and CH3Hg-S-Cys, respectively. Based on endogenous concentrations of intracellular glutathione (1–10 mM), these cysteine S-conjugates of mercury are likely to be among the major species of Hg present in cellular systems. It should be noted that inhaled Hg0 is oxidized rapidly in blood and tissues [18]. For convenience, methylmercuric species are depicted here as CH3Hg+ even though it is recognized that methylmercuric species are normally found bonded to an anion or sulfur-containing molecule.