Study on the interaction between 3 flavonoid compounds and alpha-amylase by fluorescence spectroscopy and enzymatic kinetics.

The interaction between alpha-amylase and 3 flavonoid compounds from tartary buckwheat bran, namely, quercetin (Que), its monoglycoside isoquercetin (Iso), and its diglycoside rutinb (Rut), has been studied by fluorescence spectroscopy and enzymatic kinetics. The results indicate that Que, Iso, and Rut could bind with alpha-amylase to form a new complex, which exhibits an obvious fluorescence quenching. We deduce that such a quenching is a static quenching via nonradiation energy transfer. Results from plots and calculations show that the sequence of binding constants (KA) is Iso > Que > Rut. Calculation on thermodynamic parameters reveals that the main driving force of above-mentioned interaction is hydrophobic. Enzyme activity measurements show that all of the 3 flavonoid compounds are effective inhibitors toward alpha-amylase, and the inhibitory mode belongs to a competitive type. The sequence of affinity (1/Ki) is in accordance with the results of binding constants (KA) from fluorescence experiments.