Pepsin is the first protease that food proteins encounter in the digestive tract. However, most of the previous studies on the enzymatic kinetics of pepsin were based on the hydrolysis of small synthetic peptides, due to the limitations in methodology and the complexity of protein substrate. To better understand the role of pepsin in protein digestion, we used isothermal titration calorimetry to study the enzymatic kinetics of pepsin with bovine serum albumin as the substrate. We found that pepsin has a higher catalytic rate at lower pH, while its affinity to substrate is lower. At the same pH, pepsin has lower activity and affinity at higher ionic strengths. We found contrasting kinetic parameters for pepsin-catalyzed hydrolysis of bovine serum albumin and of small synthetic peptides. Time-dependent kinetics also showed that pepsin has lower efficiency towards intermediate peptides during hydrolysis.

胃蛋白酶是食物蛋白在消化道中遇到的第一种蛋白酶。然而，由于方法学上的局限性和蛋白质底物的复杂性，以前大多数关于胃蛋白酶的酶动力学研究都是基于小的合成肽的水解。为了更好地了解胃蛋白酶在蛋白质消化中的作用，我们使用等温滴定热法研究了以牛血清白蛋白为底物的胃蛋白酶的酶动力学。我们发现胃蛋白酶在较低的pH值下具有较高的催化速率，而对底物的亲和力较低。在相同的pH值下，胃蛋白酶在较高的离子强度下具有较低的活性和亲和力。我们发现胃蛋白酶催化的牛血清白蛋白和小的合成肽水解的动力学参数相反。