Abstract: In order to determine whether Se(Ⅳ) affects the Cr(Ⅵ)-protein (bovine serum albumin, BSA) interaction system, and reduces the toxic effect of Cr(Ⅵ) on proteins, ultraviolet and fluorescence spectra were used to study the effect of Se(Ⅳ) on Cr(Ⅵ)-BSA interaction spectral characteristics, including binding characteristics, forces type, binding sites, etc. The results indicated that the addition of Cr(Ⅵ) increased the intensity of ultraviolet absorption peak of BSA, accompanied by red-shift and changes of spatial conformation. It could be deduced that there were some changes in the BSA conformation when Cr(Ⅵ) was bound to BSA. In addition, Se(Ⅳ) had no significant effect on the conformation and spectral characteristics of BSA. Cr(Ⅵ) resulted in fluorescence quenching of BSA, which was caused by the generation of substrates (1∶1) with no fluorescence. The binding constant of Cr(Ⅵ)-BSA was 4.568 8×10³ L·mol^-1 (298 K) and the quenching method belonged to static quenching. The thermodynamic parameters including enthalpy change (△H=-53.528 kJ·mol^-1), entropy change (△S=-0.110 kJ·mol^-1·K^-1) and Gibb's free energy (△G<0) were calculated using Van't Hoff equation. These negative values showed that hydrogen binding and van der Waals forces were the main interaction forces in the binding of Cr(Ⅵ) to BSA and the stabilization of the complex. Moreover, the interaction of Cr(Ⅵ) and BSA was spontaneous. Further studies revealed that the binding distance of BSA-Cr (Ⅵ) was 0.14 nm and the binding site was site II. The addition of Se(Ⅳ) had no significant effect on the conformation and spectral characteristics of BSA in BSA-Cr(Ⅵ) interaction system.

Key words: selenium, chromium, bovine serum albumin, spatial conformation, spectral characteristics