The interaction between ciprofloxacin hydrochloride (CPFX) and trypsin was investigated by fluorescence and UV absorption spectroscopy and molecular modeling methods at different temperatures (288, 298 and 308 K). Results obtained in the study indicate that CPFX has a strong ability to quench the intrinsic fluorescence of trypsin through a static quenching procedure. The fluorescence data were treated by using the double logarithmic equation, and the binding constants K of the interaction of CPFX with trypsin and the number of binding sites n were obtained. With the UV absorption spectrum, the changes of the conformation of trypsin caused by CPFX were analyzed. The thermodynamic parameters of the interaction between CPFX and trypsin at different temperatures were calculated with thermodynamic equations, which show that the binding forces between CPFX and trypsin are mainly hydrophobic interaction and hydrogen bonding. The result of molecular modeling is in good agreement with that of the thermodynamic study.

Key words: ciprofloxacin hydrochloride, trypsin, fluorescence quenching, UV absorption spectrum, molecular modeling