Inhibitory Effects of Two Polysaccharides from Highland Barley on the Activity of Pancreatic α-Amylase

Abstract

In this study, two common cereal polysaccharides, arabinoxylan (HBAX) and β-glucan (HBBG), were prepared from the bran and endosperm of highland barley, respectively. The inhibitory effects, modes and types of the two polysaccharides on pancreatic α-amylase and their interactions with the enzyme were investigated by enzymatic kinetics and fluorescence quenching analysis. The results showed that both HBAX and HBBG effectively inhibited the activity of pancreatic α-amylase, the former being significantly more effective. Their inhibitory effects were both reversible, but their inhibitory types were different. HBAX presented mixed competitive and non-competitive inhibition, indicating that it not only can bind to the active sites of the enzyme, but also can form an enzyme-starch-inhibitor complex to block the enzymatic reaction. HBBG exhibited a mixed type of anti-competitive and non-competitive inhibition, suggesting that HBBG could only bind to the inactive sites of the enzyme to form an enzyme-starch-inhibitor complex. The fluorescence quenching results revealed that both HBAX and HBBG could interact with pancreatic α-amylase and quench its endogenous fluorescence statically. However, HBAX showed significantly higher affinity to the enzyme than HBBG, and could affect the polarity of the internal hydrophobic environment of pancreatic α-amylase, and in turn affect its microstructure. In conclusion, the differences in the inhibitory effects of HBAX and HBBG on the activity of pancreatic α-amylase might be related to their different inhibitory types and affinities to the enzyme. This study will provide a theoretical basis for the application of highland barley polysaccharides in the regulation of starch digestion and in low glycemic index foods.

Keywords

• highland barley; arabinoxylan; β-glucan; pancreatic α-amylase; enzymatic inhibition kinetics; fluorescence quenching