Free energy relationships of substrate and solvent hydrophobicities on enzymic catalysis in organic media

Organic solvent changes the chymotrypsin specificity with respect to nucleophiles

In alpha-chymotrypsin-catalyzed acyl-transfer reactions in water the specificity of the enzyme (the nucleophile reactivity of amino acid amides) is correlated with the substrate hydrophobicity and increases as the hydrophobicity of the side chain of the amino acid amides is increased. In a low water system (4% H2O) bulky amino acid amides are less efficient nucleophiles. The specificity of alpha-chymotrypsin towards the amino acid amides in acyl transfer reactions in this case does not depend on the hydrophobicity of the amino acid side chains but correlates with their size. Therefore, different factors can be responsible for the specificity of enzymes in water and in a mainly organic medium.

Non-aqueous enzymology

Compelling evidence has been obtained during the past year that enzymes retain their native active-site structure in organic solvents, and yet the properties of the solvent significantly affect enzyme kinetics. Fundamental advances in enzymatic catalysis in monophasic organic media are discussed and selected applications in the areas of asymmetric, polymer and chemoenzymatic syntheses are highlighted.