Binding sites for the (Hg-Se) complex on selenoprotein P.

The mechanism underlying the interaction between mercury (Hg), selenium (Se) and selenoprotein P (Sel P) in the bloodstream has been explained by the formation of the [(Hg-Se)n]m-Sel P complex. In the present study, the binding sites for the (Hg-Se)n complex on Sel P were studied by competitive assay of the binding of the (Hg-Se)n complex to Sel P with polymeric and monomeric amino acids with simultaneous detection of the Hg, Se of selenite origin and Se of Sel P origin by the high performance liquid chromatography-inductively coupled argon plasma-mass spectrometry method. The specific binding of the (Hg-Se) complex but not Hg2+ or selenide to Sel P was explained by the unique binding sites consisting of the cationic and anionic ends such as imidazolyl and selenol groups on Sel P, respectively. The number, n, in the (Hg-Se)n complex was estimated to be approx. 100, while the number, m, in the [(Hg-Se)n]m-Sel P complex was estimated to be 35. The formation of the unit complex (Hg-Se)100, followed by its binding to Sel P at up to the 35 binding sites on Sel P was suggested.