Simultaneous reduction and mercuration of disulfide bonds by monovalent mercury

Redox activities of mercury-thiol complexes: implications for mercury-induced porphyria and toxicity

Mercury exposure causes oxidative damage to the kidney, resulting in numerous biochemical changes, including the excretion of excess porphyrins in the urine (porphyrinuria). Hg(II)-induced porphyrinuria may occur, in part, by the previously reported oxidation of reduced porphyrins (porphyrinogens) by a GSH/Hg(II) complex and H2O2. To further elucidate the mechanism(s) of porphyrinogen oxidation by GSH, Hg(II), and H2O2, we compared the ability of several thiol compounds and peroxides to substitute for GSH or H2O2, respectively, in the oxidation of uroporphyrinogen (urogen). Every thiol compound tested resulted in enhanced urogen oxidation in the presence of Hg(II) and H2O2, albeit at different rates. Additionally, t-butyl or cumene hydroperoxide substituted for H2O2 in promoting urogen oxidation, although neither peroxide was as effective in this regard. Mercury-thiol complexes synthesized from Hg(I) and GSSG also promoted urogen oxidation in the presence of H2O2. Additionally, in the absence of urogen, both GSH/Hg(II) or GSSG/Hg(I) catalyzed the decomposition of H2O2. Finally, incubation of GSH/Hg(II) or GSSG/Hg(I) with H2O2 resulted in HPLC-detectable products distinct from GSH, GSSG, or GS2Hg(II). These findings suggest that mercury-thiol complexes possess redox activity in biological systems, which promotes the oxidation of porphyrinogens and possibly other biomolecules.

In vitro assessment of the toxicity of metal compounds : IV. Disposition of metals in cells: Interactions with membranes, glutathione, metallothionein, and DNA

This review has focused on several parameters related to the delivery of carcinogenic metal compounds to the cell nucleus as a basis for understanding the intermediates formed between metals and cellular components and the effect of these intermediates on DNA structure and function. Emphasis has been placed on metal interactions at the cellular membrane, including lipid peroxidation, metal interactions with glutathione and their relation to membrane injury, and metal effects on the membrane bound enzyme, Na(+)/K(+) ATPase. Metal binding to metallothionein is also considered, particularly as related to transport and utilization of metal ions and to genetic defects in these processes exemplified in Menkes disease. The ability of cadmium to induce the synthesis of metallothionein more strongly than zinc is also discussed in relation to other toxic and carcinogenic metals. The effects of metal ions on purified DNA and RNA polymerase systems are presented with some of the recent studies using biological ligand-metal complexes. This review points out the importance of considering how metals affect in vitro systems when presented as ionic forms or complexed to relevant biological ligands.