Shimamoto N
J Biochem. 1977 Jul;82(1):185-93. doi: 10.1093/oxfordjournals.jbchem.a131668.
A detailed examination of the mechanism of the hydrolysis of phenyl acetates by alpha-chymotrypsin [EC 3.4.21.1] was carried out. The effective deacylation rate constants of some phenyl acetates obtained by titration of the acetyl-enzyme decreased at low substrate concentrations and showed anomalous pH dependences and solvent isotope effects. The transient kinetics of deacylation of the acetyl-enzyme were biphasic. A spectrum and a breakdown rate similar to those of acetylimidazole were observed when the acetyl-enzyme was denaturated with sodium dodecyl sulfate. These results indicate the participation of histidine-acylated enzyme, which woud account for the anomalous phenomena previously found in this system, including a large value of Hammett's rho. The relation between the substrate activation and the two intermediates is discussed.
对α-胰凝乳蛋白酶[EC 3.4.21.1]催化乙酸苯酯水解的机制进行了详细研究。通过滴定乙酰化酶得到的一些乙酸苯酯的有效脱酰速率常数在低底物浓度下降低，并表现出异常的pH依赖性和溶剂同位素效应。乙酰化酶脱酰的瞬态动力学是双相的。当用十二烷基硫酸钠使乙酰化酶变性时，观察到与乙酰咪唑相似的光谱和分解速率。这些结果表明组氨酸酰化酶的参与，这可以解释该系统中先前发现的异常现象，包括哈米特ρ值较大。讨论了底物活化与两种中间体之间的关系。
