Under the imitated physiological condition of animal body, the binding of paraquat to bovine serum albumin (BSA) was studied by fluorescence spectrum and ultra-violet spectrum. It was shown that this compound has a quite strong ability to quench the fluorescence launching from BSA. After analyzing the fluorescence quenching data according to Stern-Volmer equation and Lineweaver-Burk double-reciprocal equation, we found that BSA had reacted with paraquat and formed a certain new compound. The quenching belonged to static fluorescence quenching, with non-radiation energy transfer happening within single molecule. The binding locality was an area 2.07 nm away from tryptophan residue-212 in BSA based on F?rster’s non-radiation energy transfer mechanism. According to Lineweaver-Burk equation, K_LB (297 K: 2.035×10⁴ L•mol^－1; 304 K: 3.256×10⁴ L•mo^－1; 311 K: 2.889×10⁴ L•mol^－1), the forming constants of the compound at different temperatures and the thermodynamic parameters (⊿H^Ø＝18.50 kJ•mol^－1; ⊿S^Ø＝144.7 J•K^－1/145.2 J•K^－1/141.0 J•K^－1; ⊿G^Ø＝－24.50 kJ•mol^－1/－25.66 kJ•mol^－1/－25.36 kJ•mol^－1) at correspondence temperatures were obtained. The latter shows that binding power between them is mainly the hydrophobic interaction. The effect of paraquat on the conformation of BSA was analyzed by three-dimensional fluorescence spectra, contour spectra and synchronous spectra, and some useful information was offered for preventing animals from infecting paraquat and curing those who had caught it.

Key words: paraquat, bovine serum albumin, binding reaction, thermodynamic parameter, absorption spectra, three-dimensional fluorescence spectra