Modification of the Microenvironment of Enzymes in Organic Solvents. Substitution of Water by Polar Solvents

Enzyme catalysis in water-immiscible organic solvents is strongly influenced by the amount of water present in the reaction mixture. Effects of substitution of part of the water by other polar solvents were studied. In an alcoholysis reaction catalyzed by chymotrypsin deposited on celite, it was possible to exchange half of the water by formamide, ethylene glycol or dimethyl sulfoxide with often increased initial reaction rate. Furthermore, these substitutions caused the suppression of the competing hydrolysis reaction. However, formamide caused enzyme inactivation, and ethylene glycol participated as a reactant in the alcoholysis to some extent, hence dimethyl sulfoxide was considered the best water substitute among the solvents tested. These effects were noted for chymotrypsin catalyzed alcoholysis in several water immiscible solvents and also for interesterification reactions catalyzed by Candida cylindracea lipase on celite. In the latter case a change in the stereoselectivity was observed. At a low water content a high stereoselectivity was observed; when the amount of polar solvent was increased, either by doubling the water content or adding an equal amount of DMSO, the stereoselectivity decreased.