CASTANEDA-AGULLO M, DEL CASTILLO L M
J Gen Physiol. 1959 Jan 20;42(3):617-34. doi: 10.1085/jgp.42.3.617.
The use of aqueous alkali for the titration of esterolytic activity when the esters are dissolved in alcoholic solutions, results in an error due to changes in the ionization of the buffer. This is corrected by titrating with alkali in the same solvent as the substrate. Alcohols and other substances which change the dielectric strength of water modify the rate of hydrolysis of BAEE(1) and TSAME by trypsin to an extent proportionate to their effect on the dielectric strength. The reaction rate increases with diminished dielectric strength and vice versa. At low concentrations of substance there seems to be no specific effect other than that derived of the variation in dielectric strength. At higher concentrations, the enzyme might be denatured. In addition, it is probable that specific effects of each substance might intervene. The Coulombic and thermic energies of activation were calculated for the two esters in various solvents. The plot of the logarithm of rate constant vs. reciprocal of dielectric constant yields a straight line with positive slope. This behavior is similar to that of a non-enzymatic positive ion-dipole reaction. Trypsin reacts like a positive ion. The possible influence of the dielectric strength on the regulation of the equilibria involved in the interconversion of the various forms of trypsin in solution (active, inactive, denatured) is discussed.
当酯溶解于醇溶液中时，使用碱水溶液滴定酯解活性会因缓冲液电离的变化而导致误差。通过在与底物相同的溶剂中用碱进行滴定可对此进行校正。醇类及其他改变水介电强度的物质会使胰蛋白酶对苯甲酰-L-精氨酸乙酯（BAEE）(1)和对甲苯磺酰-L-精氨酸甲酯（TSAME）的水解速率改变，其程度与它们对介电强度的影响成比例。反应速率随介电强度降低而增加，反之亦然。在低浓度物质时，除了介电强度变化产生的影响外，似乎没有其他特定影响。在较高浓度时，酶可能会变性。此外，每种物质的特定影响可能也会起作用。计算了两种酯在各种溶剂中的库仑活化能和热活化能。速率常数的对数与介电常数的倒数作图得到一条斜率为正的直线。这种行为类似于非酶正离子-偶极反应。胰蛋白酶的反应类似于正离子。讨论了介电强度对溶液中各种形式胰蛋白酶（活性、无活性、变性）相互转化所涉及平衡调节的可能影响。
