α-Glucosidase inhibitors derived from black soybean and their inhibitory mechanisms

Various studies have documented the beneficial effects of black soybean extract against diabetes. However, the specific active compounds responsible for these effects remain elusive. Here, we aimed to identify the α-glucosidase inhibitors present in black soybeans using affinity ultrafiltration. Seven isoflavones with α-glucosidase inhibitory activity were identified, among which daidzein and genistein demonstrated remarkably superior inhibitory activity compared to that of acarbose (IC 50  = 632.5 ± 70.0 μmol/L), exhibiting IC 50 values of 15.7 ± 0.3 and 3.2 ± 1.2 μmol/L, respectively. An analysis of the structure-activity relationship revealed a negative correlation between the degree of glycosylation of isoflavone and α-glucosidase inhibitory activity. Enzyme kinetic studies revealed that both daidzein and genistein acted as uncompetitive inhibitors of α-glucosidase. Additionally, these compounds effectively suppressed the intrinsic fluorescence of α-glucosidase through the static quenching mechanism. The interaction between daidzein or genistein and α-glucosidase involves spontaneous formation of a complex, which is driven by hydrophobic interactions and hydrogen bonds. These findings provide valuable insights into the molecular mechanisms underlying the α-glucosidase inhibitory activity of black soybean isoflavones.