Activity and Stereoselectivity of Redox Enzymes in Organic Solvents

Massachusetts Institute Of Technology, Cambridge MA

Investigators

Abstract

0094715 Klibanov This project is to expand the scope of nonaqueous stereoselective biocatalytic conversions to include oxidoreductases, another biotechnologically promising class of enzymes. It will include the investigation of asymmetric oxidations of organic sulfides (thioethers) to chiral sulfoxides and reductions of chiral hydroperoxides to chiral alcohols catalyzed by the model enzyme horseradish peroxidase (HRP) in organic solvents. For both of these enzymatic processes, the rates and stereoselectivities will be kinetically examined as a function of the solvent in order to identify the solvent's most influential parameters. In these studies, HRP will be suspended in organic solvents either as a lyophilized powder (the most common mode of enzyme use in nonaqueous media) or as lightly cross-linked crystals (in which enzymes tend to retain their native structure in organic solvents). The cross-linked crystal mode will allow a test of the hypothesis that the solvent dependence of HRP's stereoselectivity is primarily due to the differential energetics of substrate desolvation in the corresponding enzyme-bound transition states. This will be accomplished by combining the kinetic analysis with structure-based molecular modeling, followed by semiempirical thermodynamic calculations. Additional complementary strategies for enhancing HRP catalysis in organic solvents will be explored, including bioimprinting with a variety of ligands and temporarily engaging the substrate in reversible molecular complexes.