Inhibition kinetics and mechanism of genistein against α-glucosidase

Abstract

Several studies have documented the effective inhibition of genistein, a component in soybeans against α-glucosidase. However, the details of the inhibition mechanism and kinetics remain unfulfilled. Here, the authors aim to investigate the antidiabetic potential of genistein through IC₅₀ value, fluorescence quenching and inhibition kinetics. Genistein was found to exhibit an inhibition activity on α-glucosidase with an IC₅₀ value of 7.79±0.36 µm. Analysis of fluorescence spectra indicated that genistein quenched enzyme emission through a static mechanism with a bimolecular quenching constant, Kq = 4.04 x 10¹³ M⁻¹ S⁻¹. In addition, it was found that genistein was bound to α-glucosidase with a high affinity of binding constant, Ka = 3.38 x 105 M⁻¹ S⁻¹ and a 1:1 stoichiometric ratio (n = 1.06). In order to suggest a possible contact involved, 8-anilino-1-naphthalenesulfonic acid (ANS) was added as an extrinsic fluorescence probe to enzyme solution and analyzed fluorescence spectra of the α-glucosidase-ANS complexes. When treated with genistein, fluorescence intensities of the complexes were reduced remarkably, indicating that genistein interacts with the enzyme via a hydrophobic domain. Finally, the inhibition constant and inhibition mode were studied by inhibition kinetics. The results revealed that genistein bound easily to α-glucosidase with a Ki value of 25.61 x 10⁻⁶ M through a non competitive type.