Abstract：
To elucidate why the inhibitory activity of one same polyphenol against α-amylase varies in different works. Seven starchy and three artificial substrates, and a polyphenolic competitive inhibitor, tannic acid (TA) were applied to study the enzyme inhibition in different digestion systems. The results showed that the IC50 values of TA were similar for all starches at the same starch concentration, although there existed difference in starch physiochemical properties, like branching degree, amylose chain distribution, viscosity, and digestion rate. However, the IC50 values significantly decreased with the substrate concentration decreasing, regardless of substrate types. Notably, TA had a similar competitive inhibition constant (Kic) for all the starches, despite the difference in substrate concentration, indicating that the fixed constant unconditionally describes the inhibitor-enzyme binding property. In the TA/amylase/starch system, the physical adsorption of TA with starch was much weaker than the specific binding of TA with α-amylase that was driven by hydrogen bondings and π-stackings. Therefore, it was the substrate, i.e., α-1,4-glucosidic bond concentration, rather than the existing matrix of the bonds, that predominantly affected the inhibitory activity of a polyphenol, because of the competitive action between α-1,4-glucosidic bond and the polyphenol regarding binding with the enzyme.
摘要：
为了阐明为什么相同的多酚对α-淀粉酶的抑制活性在不同的工作中有所不同。七个淀粉和三个人造底物，和多酚竞争性抑制剂，应用单宁酸（TA）研究了酶在不同消化体系中的抑制作用。结果表明，在相同的淀粉浓度下，所有淀粉的TA的IC50值相似，虽然淀粉理化性质存在差异，像分支度，直链淀粉链分布，粘度,和消化率。然而,IC50值随着底物浓度的降低而显著降低,无论基材类型。值得注意的是,TA对所有淀粉都有相似的竞争抑制常数(Kic)，尽管底物浓度不同，表明固定常数无条件地描述抑制剂-酶结合性质。在TA/淀粉酶/淀粉体系中，TA与淀粉的物理吸附比TA与α-淀粉酶的特异性结合弱得多，后者是由氢键和π堆叠驱动的。因此,它是基质，即，α-1,4-糖苷键浓度，而不是现有的债券矩阵，主要影响多酚的抑制活性，由于α-1,4-糖苷键与多酚之间关于与酶结合的竞争作用。
