Predicting enzyme behavior in nonconventional media: correlating nitrilase function with solvent properties

The insolubility of nitrile substrates in aqueous reaction mixture decreases the enzymatic reaction rate. We studied the interaction of fourteen water miscible organic solvents with immobilized nitrile hydrolyzing biocatalyst. Correlation of nitrilase function with physico-chemical properties of the solvents has allowed us to predict the enzyme behavior in such non-conventional media. Addition of organic solvent up to a critical concentration leads to an enhancement in reaction rate, however, any further increase beyond the critical concentration in the latter leads to the decrease in catalytic efficiency of the enzyme, probably due to protein denaturation. The solvent dielectric constant (epsilon) showed a linear correlation with the critical concentration of the solvent used and the extent of nitrile hydrolysis. Unlike alcohols, the reaction rate in case of aprotic solvents could be linearly correlated to solvent log P. Further, kinetic analysis confirmed that the affinity of the enzyme for its substrate (K (m)) was highly dependent upon the aprotic solvent used. Finally, the prospect of solvent engineering also permitted the control of enzyme enantioselectivity by regulating enantiomer traffic at the active site.