Developments and trends in enzyme catalysis in nonconventional media.

The conventional notion that enzymes are only active in aqueous media has long been discarded, thanks to the numerous studies documenting enzyme activities in nonaqueous media, including pure organic solvents and supercritical fluids. Enzymatic reactions in nonaqueous solvents offer new possibilities for producing useful chemicals (emulsifiers, surfactants, wax esters, chiral drug molecules, biopolymers, peptides and proteins, modified fats and oils, structured lipids and flavor esters). The use of enzymes in both macro- and microaqueous systems has been investigated especially intensively in the last two decades. Although enzymes exhibit considerable activity in nonaqueous media, the activity is low compared to that in water. This observation has led to numerous studies to modify enzymes for specific purposes by various means including protein engineering. This review covers the historical developments, major technological advances and recent trends of enzyme catalysis in nonconventional media. A brief description of different classes of enzymes and their use in industry is provided with representative examples. Recent trends including use of novel solvent systems, role of water activity, stability issues, medium and biocatalyst engineering aspects have been discussed with examples. Special attention is given to protein engineering and directed evolution.