Interaction between Selenomethionine and Copper Ions

The binary Cu-selenomethionine (SeMet) complex was investigated using voltammetry and chronocoulometry. A pair of peaks (V, VI) were observed at -132 and 71 mV in the Cu(NO3)(2) solution. When SeMet and Cu(NO3)(2) coexisted, four peaks (I, II, III, and IV) were observed at 14, 128, 271, and -194 mV, respectively. From the 600 to -600 mV potential scan, we observed that the Cu(II)-(SeMet)(2) complex was reduced to Cu(I)-SeMet complex at 14 mV and then the Cu(I)-SeMet complex was reduced to Cu(0) and SeMet at -194 mV. After reaching -600 mV the potential was reversed and the reduced product was oxidized to the Cu(I)-SeMet complex at 128 mV and Cu(II)-(SeMet)(2) complex at 271 mV. The Cu(I)-SeMet complex was stable from about -100 to 200 mV and a redox process was observed for Cu(I). The stability constants of the binary Cu-SeMet complex, 2.24x10(7) (K-1) and 2.24x10(6) (K-2), were determined by capillary electrophoresis. We proposed the structures of Cu-SeMet complexes: Copper coordinated with SeMet by the formation of Cu-Se and Cu-OCO bonds at pH 3.9 or by the formation of Cu-N and Cu-OCO bonds under physiological conditions.