Structural basis of the antagonism between inorganic mercury and selenium in mammals

Mercuric chloride toxicity in mammals can be overcome by co-administration of sodium selenite. We report a study of the mutual detoxification product in rabbit plasma, and of a Hg-Se-S-containing species synthesized by additi on of equimolar mercuric chloride and sodium selenite to aqueous, buffered glutathione. Chromatographic purification of this Hg-Se-S species and subse quent structural analysis by Se and Hg extended X-ray absorption fine struc ture (EXAFS) spectroscopy revealed the presence of four-coordinate Se and H g entities separated by 2.61 Angstrom. Hg and Se near-edge X-ray absorption spectroscopy of erythrocytes, plasma, and bile of rabbits that had been in jected with solutions of sodium selenite and mercuric chloride showed that Hg and Se in plasma samples exhibited X-ray absorption spectra that were es sentially identical to those of the synthetic Hg-Se-S species. Thus, the mo lecular detoxification product of sodium selenite and mercuric chloride in rabbits exhibits similarities to the synthetic Hg-Se-S species. The underly ing molecular mechanism for the formation of the Hg-Se-S species is discuss ed.