基于分子机制的蛋白质酶解反应经验修饰动力学模型

蛋白质酶解反应动力学行为的复杂性在于体系中底物与产物的多样性,以及由此决定的动力学常数的可变性.基于此,以酪蛋白(case in)—胰蛋白酶(trypsin)为模式体系,拟合求得动力学常数(Km和kcat)随水解度(DH)值变化的函数表达式,其规律为:随DH值增加,Km增大,kcat减小,kcat/Km减小,证明:酶与底物的亲和力随肽链缩短而减小,即高分子量多肽为蛋白酶的适宜底物,而酶解效率与酶解专一性随反应进行逐渐降低.进一步,根据分子水平的蛋白质酶解作用机制,关联水解实验数据,得到case in-trypsin酶解反应的经验修饰动力学方程(模型平均相对误差<5%),为定量表征复杂酶解历程以及高效制备活性多肽提供了理论基础.

An Experimentally Modified Kinetic Model for Enzymatic Hydrolysis of Protein to Prepare Active Peptides Based on Molecular Mechanism

The kinetics of casein tryptic hydrolysis was studied for preparation of active peptides.It is assumed that(1) the apparent kinetic constants,K_(m) and k_(cat),vary with degree of hydrolysis,i.e.average peptide length of substrate,2 the total concentration of substrate remains constant during the whole reaction,and3 every elementary reaction still follows the M-M equation.Based on the molecular mechanism of enzymatic hydrolysis and the(above) assumptions,a set of experimentally modified kinetic equations was established by correlating initial concentration of substrate(s_(0)),enzyme concentration(e_(0)),degree of hydrolysis(DH) and reaction time(t).The relative error of fitted results was less than 5%,which was in good agreement with the experimental data.Furthermore,according to the simulated functional relationship between apparent kinetic constants and DH value,i.e.as DH increased,K_(m) increased,but k_(cat) and k_(cat)/K_(m) decreased,it was demonstrated that the affinity of peptide and enzyme,the efficiency of enzymatic hydrolysis and the specificity of protease all decreased as reaction proceeded.