BIOCATALYSIS IN ORGANIC MEDIA

It is now accepted that organic media are widely applicable to biocatalytic processes. Enzyme reactions have been demonstrated in many different solvent systems containing apolar solvents with a wide range of hydrophobicities. In such systems the aqueous fraction of the solvent may vary from trace levels (the "microaqueous" reaction system) to the major constituent. The properties of enzymes in media containing both aqueous and apolar constituents are influenced by many factors including the dielectric constant, the concentration or "activity" of water, the presence of phase-interfaces, etc. All of these factors influence the structural stability of the enzyme to some degree and optimization of enzyme-stability in response to these factors is of critical importance in the design of any organic-solvent biocatalytic system. The presence of apolar solvents, even at low concentrations, may influence protein structure at a more subtle level, resulting in significant changes in reaction kinetics, substrate specificity and stereoselectivity. Thus "solvent engineering" can be used to exert control over reaction mechanisms, product spectrum and yield In order to take full advantage of the effects of different solvents on enzyme function in designing reaction systems, an understanding of the molecular interactions between solvent and protein is essential. For example, a detailed knowledge of the role of protein solvation shell water and the distortion of this shell by hydrophilic organic solvents may assist in the design of "solvent resistant" enzymes. Similarly, the inferred influence of low water content solvents on conformational mobility may permit us to select solvent systems which will optimise the chemical and optical purity of the reaction products.