Insight into the binding modes and mechanisms of inhibition between soybean-peptides and α-amylase based on spectrofluorimetry and kinetic analysis

Abstract The inhibitory effects of soybean peptides (SPTs) with four different molecular weights (MWs) (SPT1, SPT2, SPT3, and SPT4) on porcine pancreatic α-amylase (PPA) were evaluated by spectrofluorimetry and enzyme inhibition analysis. SPT1, SPT2, and SPT3 were mixed inhibitors with competitive and uncompetitive inhibitory effects on α-amylase. SPT with lower MWs inhibited PPA more strongly than those with higher MWs. SPT binding interactions with PPA were mainly non-covalent, i.e., van der Waals interactions and hydrogen-bonding. SPT interacted with Tyr, Trp and Phe residues in PPA and quenched its intrinsic fluorescence, via a static quenching mechanism. SPT of higher MW had stronger binding interactions and more stable complexes with PPA than those of lower MW. SPT1, SPT2 and SPT3 have potential inhibitory effects on PPA activity in vivo, which could delay the digestion of starchy foods. These findings have laid a theoretical foundation for slowing starch digestibility by formulation with peptides and thereby developing novel low-glycaemic index functional foods.