Analysis for inhibition mechanisms of pheophytin a and pyropheophytin a against alpha-glucosidase by multi-spectroscopy, molecular docking, and molecular dynamics simulation

Chlorophyll a (Chl a) is widely distributed in plants and undergoes conversion, pheophytin a (Pheo a) and pyropheophytin a (Pyro a), during heating or acidic treatment. This study investigated the α-glucosidase-inhibitory properties of Pyro a using multi-spectroscopy, molecular docking, and a molecular dynamics simulation, with a comparative analysis against Pheo a. Our results suggested that Pyro a (IC₅₀ = 22.79 μg/mL) showed stronger inhibitory activity than Pheo a (IC₅₀ = 39.02 μg/mL) with a mixed-type manner. Moreover, fluorescence quenching and Fourier transform infrared spectra results clarified that Pheo a and Pyro a interacted with α-glucosidase in a static quenching mode, inducing rearrangement and conformational changes of α-glucosidase. Molecular docking revealed that both Pheo a and Pyro a bind to the catalytic site of α-glucosidase, with Pyro a forming more hydrogen bonds and showing higher affinity. Molecular dynamics simulations supported the enhanced binding stability of the Pyro a–α-glucosidase complex. In conclusion, both Pheo a and Pyro a inhibit α-glucosidase by inducing structural rearrangement, with Pyro a demonstrating superior potency, likely due to its stronger and more stable interactions with the enzyme.