The interaction between ethionamide and papain was investigated by fluorescence spectroscopy, UV-Vis absorption spectroscopy and molecular simulation, and the binding constants K were obtained at different temperatures. The experimental results suggested that static quenching was the main reason for the fluorescence quenching process. Thermodynamic data showed that the change for Gibbs free energy of the binding was a large negative value, which indicated that the interaction between ethionamide and papain was driven mainly by hydrophobic force and hydrogen bond. Additionally, the effects of ethionamide on papain conformation were investigated by synchronous spectroscopy and UV-Vis absorption spectroscopy. The study of molecular simulation indicated that there was not only hydrophobic interaction on the binding of ethionamide to papain, but there was also hydrogen bond interaction, which was consistent with the results of spectra and thermodynamics.

Key words: papain, ethionamide, fluorescence spectroscopy, UV-Vis absorption spectroscopy, molecular simulation