Are water-immiscibility and apolarity of the solvent relevant to enzyme efficiency?

The question of whether the solvent's water-immiscibility is relevant to enzymatic activity was addressed by assaying four different hydrolases (three lipases and one protease) in nine anhydrous solvents of similar hydrophobicities of which four were infinitely miscible with water and five were not. For no enzyme was a jump in activity observed upon a transition from water-miscible to water-immiscible solvent. The relevance of solvent apolarity to enzymatic efficiency was also examined. To this end, three groups of isomeric anhydrous solvents were selected where within each group of isomeric anhydrous solvents were selected where within each group one solvent was apolar (i.e., lacked a permanent dipole moment). For none of the four enzymes studied was activity significantly higher in apolar solvents than in their polar counterparts. Thus we conclude that often-cited solvent's immiscibility with water and apolarity by themselves are irrelevant to enzymatic activity. (c) 1993 John Wiley & Sons, Inc.