Abstract: Tomatidine purified from tomato leaves was identified by ultra-performance liquid chromatography-quadrupole time-of-flight mass spectrometry (UPLC-QTOF-MS) and 1H and 13C nuclear magnetic resonance (NMR). The effect of tomatidine on the activity of acetylcholinesterase was evaluated by ultraviolet (UV) spectroscopy, molecular fluorescence spectroscopy and molecular docking, and the mode of combination between tomatidine and acetylcholinesterase was explored. The results showed that the purified product was identified as tomatidine. It partially inhibited acetylcholinesterase (AChE) in a competitive manner. The molecular fluorescence spectra showed that tomatidine decreased the fluorescence emission intensity of AChE at 340 nm and led to a red shift. Molecular docking with Autodock revealed that tomatidine hydrophobically interacted with Ser293, Phe295, Phe338, Phe297, Ser125, Gly121, Ser203, Glu202, Gly120, His447, Gly448, Ile451, Trp86, Tyr124, Tyr337, Tyr341 and Ile294 in AChE, and formed hydrogen bonds with Trp86, indicating that the microenvironment of AChE was changed, competitively interfering with the binding of the substrate acetylcholine to AChE. Therefore, tomatidine can inhibit the activity of AChE by forming hydrogen bonds as well as through hydrophobic interactions.

Key words: tomatidine; acetylcholinesterase; enzyme activity; competitive inhibition; molecular docking