Dielectric effects and transesterification reactions catalyzed by trypsin

Abstract

1. 1. A comparative study has been made of the effect of two solvent systems, aqueous acetone and n propanol, on the trypsin-catalyzed hydrolysis of l-lysine methyl ester (LME). 2. 2. The use of acetone, which does not compete with water as an acceptor of the acyl group, made it possible to ascertain that the rate of this reaction depended on the gross dielectric constant of the medium in the same manner as the rates previously observed in the trypsin catalyzed hydrolysis of benzoyl- l-arginine ethyl ester (BAEE) and p- toluenesulfonyl- l- arginine methyl ester (TAME), viz., the reaction was accelerated in media of low dielectric constant and decelerated in media of high dielectric constant. 3. 3. The effect of n-propanol was converted progressively from inhibitory to enhancing as pH increased, passing through a transition between pH 7 and 7.5. 4. 4. A trypsin-catalyzed transesterification reaction took place between LME and n-propanol which resulted in the formation of l-lysine propyl ester. Similar transesterification products of BAEE or TAME could not be detected. 5. 5. The predominance of the transesterification effect of alcohols over the dielectric one at low pH values was apparently related to the degree of ionization of the alpha ammonium group of LME.