Probing the Interaction between Acotiamide Hydrochloride and Pepsin by Multispectral Methods, Electrochemical Measurements, and Docking Studies.

The interaction between acotiamide hydrochloride and pepsin was systematically characterized by fluorescence and electrochemical approaches. Fluorescence lifetime measurements showed that acotiamide hydrochloride quenched the intrinsic fluorescence of pepsin with a new complex formation via static mode, which was reconfirmed by cyclic voltammetry results. Both of the binding number and binding constants were calculated from differential pulse voltammetry analysis and fluorescence spectroscopy. The values obtained from the above two methods displayed a relatively high degree of consistency. Thermodynamic parameters suggested that acotiamide hydrochloride interacted with pepsin spontaneously by hydrogen bonding and van der Waals interactions. These results were consistent with the results obtained from molecular docking analysis. As revealed by synchronous fluorescence, three-dimensional fluorescence, Fourier transform infrared spectrometry, and circular dichroism spectra, acotiamide hydrochloride could affect the microenvironment and slightly change the secondary structure of pepsin. Furthermore, acotiamide hydrochloride can inhibit pepsin activity in vitro, as explained by the molecular docking.