Under the simulative human physiological condition, the interaction of sulfamethoxazole (SMZ) and bovine serum albumin (BSA) with or without Fe^3＋ was studied by fluorescence spectra, ultra-violet absorption spectra and FT-IR spectra. The results show that both the quenching mechanism of the intrinsic fluorescence of BSA by sulfamethoxazole with or without Fe^3＋ is a static fluorescence quenching procedure. It was found that in the presence of Fe^3＋, the binding constant of SMZ and BSA increased and the main binding force between SMZ and BSA was changed from hydrophobic force to hydrogen bonds and van der Waals force. From the synchronous fluorescence and three-dimensional fluorescence spectra, it was found that SMZ change the conformation of BSA. BSA may form a new disordered structure, but the capability of SMZ changing the structure of the BSA was not enhanced in the presence of Fe^3＋. Based on fluorescence resonance energy transfer (FRET), the distances (r) between donor (BSA) and acceptor (SMZ and Fe^3＋-SMZ) were obtained. According to FT-IR, the secondary structure of BSA changed when Fe^3＋ and SMZ were added.

Key words: bovine serum albumin, sulfamethoxazole, Fe^3＋, fluorescence spectroscopy, UV absorption spectra, Fourier transform infrared spectroscopy