Probing the interaction between 3 flavonoids and pancreatic lipase by methods of fluorescence spectroscopy and enzymatic kinetics

The interactions between pancreatic lipase and 3 flavonoids from tartary buckwheat bran, namely, quercetin (Que), its monoglycoside isoquercetin (Iso) and diglycoside rutin (Rut), had been studied by fluorescence spectroscopy and enzymatic kinetics and have also been compared with the best-selling antiobesity drug, Orlistat. The results showed that Que, Iso, and Rut all had a strong ability to quench the intrinsic fluorescence of pancreatic lipase by the formation of a new complex and nonradiation energy transfer mechanism. The sequence of binding constant (KA) was Rut > Que > Iso, and the number of binding site was one in all of the cases. The data of thermodynamic parameters at different temperatures indicated that hydrogen bonds and van der Waals forces played a major role in the previously mentioned interaction. Enzymatic kinetics measurements showed that Rut, Iso, and Que had a satisfied inhibitory ability toward pancreatic lipase in a dose-dependent manner, with the IC50 values as 0.97, 1.1, and 1.49 mg/mL and the maximum of inhibitory rate as 85, 81.2 and 67.9%. All the inhibitory modes of the 3 flavonoids belonged to noncompetitive type. The sequence of affinity (1/Ki) was Rut > Iso > Que, consistent with the inhibitory sequence.