Biocatalysis in organic media using enzymes from extremophiles

Enzymes from extremophiles (extremozymes) show activity and stability at extremes of temperature, low water activity, and high hydrostatic pressure. Aqueous/organic and nonaqueous media allow the modification of reaction equilibria and enzyme specificity, creating pathways for synthesizing novel compounds. Used in combination with such media, extremozymes show great potential as shown by their unique properties in aqueous media. This review introduces organic media biocatalysis before addressing the state of the art of recent fundamental and applied aspects of extremozyme biocatalysis. The aim is to encourage further exploitation of this technology, drawing on the limited work published in this field and important methods developed using mesophilic enzymes. Enzymes from three classes of extremophile will be considered: psychrophiles, halophiles, and thermophiles. Low temperature processes using psychrophilic (cold-active) enzymes may enhance yields of heat-sensitive products and reduce energy consumption. Halophilic enzymes require KCl/NaCl from 1 M to saturation, i.e. low water activity media, a feature in common with organic solvent systems. Thermophilic enzymes can be active and stable at up to 130 degrees C and are highly resistant to proteases, detergents, and chaotropic agents. These features may afford resistance to the effects of organic solvents. Enhancing extremozyme performance via chemical modification, complexation, immobilization, and protein engineering is also discussed. (C) 1999 Elsevier Science Inc. All rights reserved.