Comparative evaluation of quercetin, isoquercetin and rutin as inhibitors of alpha-glucosidase.

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.

[Direct determination of Cu and Pb in edible L-lysine by graphite furnace atomic absorption spectrometry].

The determination of Cu and Pb in edible L-lysine by rapid graphite furnace atomic absorption spectrometry (GFAAS) is described in this paper. The sample is dissolved with thin acid and mensurated directly by GFAAS. It does not need dry ashing and wet digesting and without chemical matrix modifier. The Graphite Furnace's function of pre-treatment is fully used. Results can be obtained as soon as possible and avoid unnecessary contamination and loss of samples. The method is simple, rapid, practical and have good precision and accurate. Under the optimum conditions the result indicates that the relative standard deviation of Cu and Pb is 4.8% and 5.3% respectively, the recovery rate is 100%-110% and 102%-105% separately.