In Vivo Formation of HgSe Nanoparticles and Hg–Tetraselenolate Complex from Methylmercury in Seabirds—Implications for the Hg–Se Antagonism

In vivo and in vitro evidence for detoxification of methylmercury (MeHg) as insoluble mercury selenide (HgSe) underlies the central paradigm that exposure is not or little hazardous when tissue Se molar excess (Se:Hg > 1). However, this hypothesis overlooks binding Hg to selenoproteins, which lowers amount bioavailable acts a reservoir MeHg, thereby underestimating toxicity mercury. This question was addressed by determining chemical forms various tissues giant petrels Macronectes spp. using combination high energy-resolution X-ray absorption near edge structure extended fine spectroscopy, transmission electron microscopy coupled elemental mapping. Three main species were identified, MeHg-cysteinate complex, four-coordinate selenocysteinate complex (Hg(Sec)4), HgSe precipitate, together with minor dicysteinate Hg(Cys)2. The decreases order liver kidneys brain = muscle, Hg(Sec)4 muscle liver. On basis biochemical considerations structural modeling, we hypothesize bound carboxy-terminus domain selenoprotein P (SelP) contains 12 Sec residues. Structural flexibility allows SelP form multinuclear Hgx(Se,Sec)y complexes, can be biomineralized protein self-assembly. Because has Se:Hg ratio 4:1, severely depletes stock synthesis activity one μg Se/g dry wet several birds. concentration still relatively because selenium naturally abundant seawater, therefore it probably does fall below metabolic need essential selenium. study shows may case terrestrial animals, first potentially injured toxicity.