Effects of organic cosolvents on enzyme stereospecificity. The enantiomeric specificity of α-chymotrypsin is reduced by high organic solvent concentrations

Abstract

The influence of a range of protic and aprotic solvents of varying polarities on the enantiomeric specificity of α-chymotrypsin has been examined using methyl (2S)- and (2R)-2-acetamido-2-phenylacetate (1) as representative L- and D-substrates. The rates of hydrolysis were determined in solutions containing up to 30% organic solvent. The addition of organic solvent reduced the overall rates of hydrolysis of (2S)- and (2R)-1 in each case, with those of the L-enantiomer (2S)-1 being affected more than those of the D-stereoisomer (2R)-1. However, the enzyme overwhelmingly retains its normal L-enantiomeric preference under all conditions surveyed. It is concluded that α-chymotrypsin, and possibly other strongly stereospecific enzymes, can be used with confidence for asymmetric synthesis or resolution purposes in aqueous solutions to which moderate (up to 40%) proportions of organic cosolvents have been added to increase solubility of hydrophobic organic substrates.