水溶性多糖酶解过程分子量变化与动力学建模

Molecular Weight Distribution and Kinetic Model for Enzymatic Hydrolysis of Water-soluble Polysaccharides

以魔芋葡甘聚糖–β-甘露聚糖酶水解体系为例,研究了水溶性多糖酶解过程中产物的分子量变化与动力学行为。利用凝胶排阻色谱法和特性粘度法,分别测定了酶解物的分子量分布和重均分子量Mw,结果表明:随着反应的进行,酶解物分子量分布先变宽再逐渐变窄,这是由酶在底物反应体系中的镶嵌式分布,不均一的底物分子序列结构与酶分子的选择性剪切,酶剪切的多种途径以及酶与底物的结合模式等四种因素共同作用的结果;初始阶段酶解物Mw先快速下降再逐渐趋于平缓,其速率与底物浓度有关;基于酶解产物重均分子量变化规律而建立的1/Mw随反应时间t变化的动力学模型,确定了常见的水溶性多糖浓度下酶解过程为零级降解,并与实验结果相当一致。

Using the size exclusion chromatography （SEC） and the intrinsic viscosity measurement, the changes in molecular weight of a water-soluble polysaccharide undergoing enzymatic hydrolysis were studied, and the enzymatic hydrolysis of the konjac glucomannan （KGM） solutions with β-mannanase was chosen as the investigated object to conduct this study. During the degradation process, the molecular weight of the enzymatic products decreases with reaction time, while the molecular weight distribution （MWD） broadens at first and then becomes narrow. According to the reaction mechanism, there are four factors which could cause the above variations of MWD： the sparsely inlaid distribution of enzyme molecules in KGM solutions, the maldistribution of mannose and glucose units on the KGM backbone, the different pathways for enzymatic cleavage of KGM and the binding pattern between enzyme and KGM. In addition, based on the Michaclis-Menton equation and the changes in the weight-average molecular weight of hydrolystates -↑Mw, a kinetic model was established to simulate the hydrolysis process, and it was demonstrated in good agreement with the experimental results. The inverse relationship between the reaction rate constant k and the concentration of polymer suggests that, for frequently-used polysaccharide concentration, the enzymatic hydrolysis is a zero-order reaction.