DEL CASTILLO L M
J Gen Physiol. 1959 Sep;43(1):127-37. doi: 10.1085/jgp.43.1.127.
The rates of hydrolysis of TrEE, TEE, and ATEE(1) by alpha-chymotrypsin were determined in media of variable dielectric strength. Many substances which modify the dielectric constant of the medium, exert additional specific effects on the reaction rate, noticeable at more or less elevated concentrations. Notwithstanding, it is possible to differentiate the dielectric and specific effects by comparing the rates in solvents of distinct nature at relatively low concentrations. Thus, the effect of varying the dielectric strength could be studied within wider ranges (DeltaD = 20 with TrEE and ca. 28 with ATEE) than in the previous study of trypsin (DeltaD = 12). The dielectric effect on alpha-chymotrypsin is the opposite of that observed with trypsin. In both cases there is a linear relationship between the logarithm of the rate of hydrolysis and the reciprocal of the dielectric constant. The slope is negative with alpha-chymotrypsin and positive with trypsin. According to expressions relating the dielectric constant to the rate in non-enzymatic reactions, the behavior of alpha-chymotrypsin is like that of a negative ion, while trypsin behaves as a positive ion. The enzyme activity appears to depend upon the arrangement of charges in the enzyme and substrate molecules, rather than on the presence of certain atomic groupings in the substrate.
在不同介电强度的介质中测定了α-胰凝乳蛋白酶对TrEE、TEE和ATEE(1)的水解速率。许多改变介质介电常数的物质，对反应速率会产生额外的特定影响，在或多或少升高的浓度下这种影响会很明显。尽管如此，通过比较在相对低浓度下不同性质溶剂中的速率，可以区分介电效应和特定效应。因此，与之前对胰蛋白酶的研究（ΔD = 12）相比，可以在更宽的范围内（TrEE时ΔD = 20，ATEE时约为28）研究改变介电强度的影响。α-胰凝乳蛋白酶的介电效应与胰蛋白酶所观察到的相反。在这两种情况下，水解速率的对数与介电常数的倒数之间都存在线性关系。α-胰凝乳蛋白酶时斜率为负，胰蛋白酶时斜率为正。根据将介电常数与非酶反应速率相关联的表达式，α-胰凝乳蛋白酶的行为类似于负离子，而胰蛋白酶的行为则像正离子。酶活性似乎取决于酶和底物分子中电荷的排列，而不是底物中某些原子基团的存在。
