On Dielectric Constant and Enzymatic Kinetics

Abstract

A study was made on the effect of glycine on systems involving trypsin and BAEE 1 or TSAME on the one hand, or a-chymotrypsin with any of the substrates BAEE, TEE, or PEE, on the other. In all cases there was a linear relationship between the rate logarithm and the reciprocal of the dielectric constant of the glycine solution. The slopes were positive in the reactions of trypsin. In those catalyzed by a-chymotrypsin, the slopes were positive at pH 6.5 or lower, and negative at pH 7.5. However, the effects of glycine differ quantitatively from those of urea or other solvents. The presence of salt modifies somewhat the glycine effects. A low ionic strength increases the effect of glycine on trypsin, but if the inhibition caused by the ionic strength is relatively strong, the addition of glycine partially neutralizes the salt effect. Addition of salt to systems containing a-chymotrypsin always resulted in a diminished effect of glycine. An attempt is made to interpret the anomalies of glycine effects on the basis of its dipolar ion structure. (10), applying the D o n n a n theory to the distribution of trypsin between molecules of undissolved gelatin and the surrounding solution, reached the conclusion that this e n z y m e behaved like a univalent positive ion. This conception of the ionic character of trypsin arose again recently 1 Throughout this paper the following abbreviations and symbols will be used: D, dielectric constant. I N T R O D U C T I O N N o r t h r o p in 1924AD/•C, dielectric increment. R/Ro, relative rate of hydrolysis. BAEE, benzoyl-L-arginine ethyl ester. TSAME, p-toluenesulfonyl-L-arginine methyl ester. TEE, L-tyrosine ethyl ester. PEE, L-phenylalanine ethyl ester.