Inhibitory mechanism of arabinoxylan and β-glucan from hull-less barley on α-amylase activity: A comparison study

Abstract

The inhibitory mechanisms of arabinoxylan (HBAX) and β-glucan (HBBG) from hull-less barley against pancreatic α-amylase were investigated using enzymatic inhibitory kinetics, multi-spectroscopy and thermodynamic analysis. Results indicated that both HBAX and HBBG effectively inhibited α-amylase activity, with HBAX exhibiting superior potency (IC50 of 3.26 mg/mL) compared to HBBG (IC50 of 13.23 mg/mL). Kinetic analysis revealed that HBAX displayed competitive and noncompetitive mixed inhibition, while HBBG predominantly exhibited noncompetitive inhibition. Interaction studies demonstrated that both HBAX and HBBG could spontaneously interact with α-amylase through hydrogen bonding and van der Waals forces, leading to structural adjustments of α-amylase, albeit without notable secondary structure alterations. However, HBAX showed stronger fluorescence quenching ability and microenvironmental modifications of α-amylase compared to HBBG. Bio-layer interferometry confirmed the stronger binding ability of HBAX to α-amylase, characterized by higher association binding constant (Ka) and lower dissociation constant (Kd) and affinity constant (KD). The lower equilibrium dissociation constant (K) and greater enthalpy change (ΔH) of HBAX to α-amylase further proved its stronger interaction with α-amylase. These differences were ascribed that HBAX inhibited α-amylase activity potentially through starch competition or physical interference, while HBBG might primarily act as physical barriers. This study enhances understanding of HBAX and HBBG in lowering starch digestion from an enzyme-inhibitory perspective.