Food Process Engineering, Wageningen University, P.O. Box 176700 AA, Wageningen, The Netherlands.
Food Funct. 2021 May 21;12(10):4570-4581. doi: 10.1039/d1fo00413a. Epub 2021 Apr 28.
Enzyme-catalysed hydrolysis is important in protein digestion. Protein hydrolysis is initiated by pepsin at low pH in the stomach. However, pepsin action and acidification happen simultaneously to gastric emptying, especially for liquid meals. Therefore, different extents of exposure to the gastric environment change the composition of the chyme that is emptied from the stomach into the small intestine over time. We assessed the susceptibility of a protein to trypsin-catalysed hydrolysis in the small intestine, depending on its pH and hydrolysis history, simulating chyme at different times after the onset of gastric emptying. Isothermal titration calorimetry was used to study the kinetics of pepsin and trypsin-catalysed hydrolysis. Bovine serum albumin (BSA) that was acidified and hydrolysed with pepsin, showed the highest extent and most efficient hydrolysis by trypsin. BSA in the chyme that would be first emptied from the stomach, virtually bypassing gastric acidity and peptic action, reduced trypsin-catalysed hydrolysis by up to 58% compared to the acidified, intact protein, and 77% less than the acidified, pepsin-hydrolysate. The least efficient substrate for trypsin-catalysed hydrolysis was the acidified, intact protein with a specificity constant (k/K) nearly five times lower than that of the acidified, pepsin-hydrolysate. Our results illustrate the synergy between pepsin and trypsin hydrolysis, and indicate that gastric hydrolysis increases the efficiency of the subsequent trypsin-catalysed hydrolysis of a model protein in the small intestine.
酶催化水解在蛋白质消化中很重要。胃中的低 pH 值下胃蛋白酶启动蛋白质水解。然而，胃排空时，胃蛋白酶作用和酸化同时发生，特别是对于液体餐。因此，不同程度地暴露于胃环境会随时间改变从小肠排空的食糜的组成。我们评估了蛋白质在小肠中对胰蛋白酶催化水解的敏感性，这取决于其 pH 值和水解历史，模拟了胃排空后不同时间的食糜。等温滴定量热法用于研究胃蛋白酶和胰蛋白酶催化水解的动力学。用胃蛋白酶酸化和水解的牛血清白蛋白 (BSA) 显示出最高的胰蛋白酶水解程度和效率。从小肠中最先排空的食糜中的 BSA，几乎绕过了胃酸度和胃蛋白酶作用，与酸化完整的蛋白质相比，胰蛋白酶催化水解减少了 58%，与酸化的胃蛋白酶水解产物相比，减少了 77%。胰蛋白酶催化水解效率最低的底物是酸化完整的蛋白质，其特异性常数 (k/K) 比酸化的胃蛋白酶水解产物低近五倍。我们的结果说明了胃蛋白酶和胰蛋白酶水解之间的协同作用，并表明胃水解提高了模型蛋白质在小肠中随后胰蛋白酶催化水解的效率。
