Investigation and comparison of the binding between tolvaptan and pepsin and trypsin: Multi-spectroscopic approaches and molecular docking.

Tolvaptan (TF), a selective arginine vasopressin V2 receptor antagonist, was approved by the Food and Drug Administration in 2009. This study mainly investigated the differences between the binding of TF with pepsin and trypsin by using a series of spectroscopy and molecular modeling methods. Thermodynamic parameters and molecular docking results suggested that the binding of TF to pepsin and trypsin were both spontaneous but driven by different forces. For pepsin, the binding was driven by hydrogen bonds and van der Waals forces; but for trypsin, it was driven by electrostatic forces and hydrophobic forces. The quenching mechanism between TF and pepsin and trypsin was investigated by fluorescence experiments and time-resolved fluorescence spectroscopy. Synchronous fluorescence and 3-dimensional fluorescence were used to investigate the micro-environmental and conformational changes of pepsin and trypsin after the insertion of TF. In addition, activity-measurement results showed that both the pepsin and trypsin activities increased with increasing TF concentration, which may help to understand the possible effect of TF on the digestion and absorption of nutrients in vivo.