New Insights into the Inhibition Mechanism of Betulinic Acid on alpha-Glucosidase

Betulinic acid (BA), an important pentacyclic triterpene widely distributed in many foods, possesses high antidiabetic activity. In this study, BA was found to exhibit stronger inhibition of alpha-glucosidase than acarbose with an IC50 value of (1.06 +/- 0.02) x 10(-5) mol L-1 in a mixed-type manner. BA bound with alpha-glucosidase to form a BA-alpha-glucosidase complex, resulting in a more compact structure of the enzyme. The obtained concentrations and spectra profiles of the components resolved by the multivariate-curve resolution-alternating least-squares confirmed the formation of the BA-alpha-glucosidase complex. Molecular docking showed that BA tightly bound to the active cavity of alpha-glucosidase, which might hinder the entrance of the substrate leading to a decline in enzyme activity. The chemical modification of alpha-glucosidase verified the results of the computer simulation that the order of importance of the four amino acid residues in the binding process was His > Tyr > Lys > Arg.