HOW CAN THE SOLVENT AFFECT ENZYME ENANTIOSELECTIVITY

Enantioselectivity of the protease subtilisin Carlsberg in the transesterification between the chiral alcohol sec-phenethyl alcohol and vinyl butyrate was found to be greatly affected by the solvent. For example, the (k(cat)/K(M))S/(k(cat)/K(M))R ratio varies from 3 in anhydrous acetonitrile to 61 in anhydrous dioxane. A mechanistic model is proposed that explains these findings. This model is supported by the experimental data obtained concerning the dependence of subtilisin's enantioselectivity on the structure of the chiral alcohol, on physicochemical characteristics of the solvent (systematic correlations were found with the dielectric constant and the dipole moment), and on such additives as water and the water mimic formamide. Similar dependencies (although of a smaller magnitude) were observed for the related enzyme subtilisin BPN'.