Three flavonoids from tartary buckwheat bran, namely, quercetin (Que), isoquercetin (Iso) and rutin (Rut), have been evaluated as alpha-glucosidase inhibitors by fluorescence spectroscopy and enzymatic kinetics and have also been compared with the market diabetes healer, acarbose. The results indicated that Que, Iso and Rut could bind alpha-glucosidase to form a new complex, which exhibited a strong static fluorescence quenching via nonradiation energy transfer, and an obvious blue shift of maximum fluorescence. The sequence of binding constants (K(A)) was Que > Iso > Rut, and the number of binding sites was one for all of the three cases. The thermodynamic parameters were obtained by calculations based on data of binding constants. They revealed that the main driving force of the above-mentioned interaction was hydrophobic. Enzymatic kinetics measurements showed that all of the three compounds were effective inhibitors against alpha-glucosidase. Inhibitory modes all belonged to a mixed type of noncompetitive and anticompetitive. The sequence of affinity (1/K(i)) was in accordance with the results of binding constants (K(A)). The concentrations which gave 50% inhibition (IC(50)) were 0.017 mmol*L(-1), 0.185 mmol*L(-1) and 0.196 mmol*L(-1), compared with acarbose's IC(50) (0.091 mmol*L(-1)); the dose of acarbose was almost five times of that of Que and half of that of Iso and Rut. Our results explained why the inhibition on alpha-glucosidase of tartary buckwheat bran extractive substance (mainly Rut) was much weaker than that of its hydrolysis product (a mixture of Que, Iso and Rut). This work would be significant for the development of more powerful antidiabetes drugs and efficacious utilization of tartary buckwheat, which has been proved as an acknowledged food in the diet of diabetic patients.

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.

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