α-Glucosidase inhibition by luteolin: kinetics, interaction and molecular docking.

α-Glucosidase is a critical associated enzyme with type 2 diabetes mellitus in humans. Inhibition of α-glucosidase is important due to the potential effect of down regulating glucose absorption in patients. In this study, the inhibitory activity of flavone luteolin on α-glucosidase and their interaction mechanism were investigated by multispectroscopic methods along with molecular docking technique. It was found that luteolin reversibly inhibited α-glucosidase in a noncompetitive manner with an IC50 value of (1.72 ± 0.05) × 10(-4) mol L(-1), and the inhibition followed a multi-phase kinetic process with a first-order reaction. Luteolin had a strong ability to quench the intrinsic fluorescence of α-glucosidase through a static quenching procedure. The positive values of enthalpy and entropy change suggested that the binding of luteolin to α-glucosidase was driven mainly by hydrophobic interactions, and the binding distance was estimated to be 4.56 nm. Analysis of synchronous fluorescence, circular dichroism, and Fourier transform infrared spectra demonstrated that the binding of luteolin to α-glucosidase induced rearrangement and conformational changes of the enzyme. Moreover, the results obtained from molecular docking indicated that luteolin had a high affinity close to the active site pocket of α-glucosidase and indirectly inhibited the catalytic activity of the enzyme.