ENZYME-CATALYZED BIOTRANSFORMATIONS IN AQUEOUS 2-PHASE SYSTEMS WITH PRECIPITATED SUBSTRATE AND OR PRODUCT/

Biotransformations catalyzed by free and immobilized enzymes have been carried out in aqueous suspensions with up to 25% (w/w) precipitated substrate or product. For the kinetically controlled synthesis of N-Ac etyl-Tyr-Arg-NH2 with up to 0.8 M insoluble activated substrate N-Acet yl-TyrOEt catalyzed by alpha-chymotrypsin (EC 3.4.21.1) the dipeptide yield was found to be >90%. This and the space-time yields were higher than those observed for one-phase aqueous systems and much higher tha n in systems where the insoluble substrate had been solubilized by add ition of organic solvents. In the equilibrium controlled hydrolysis of 0.4 M D-phenylglycine-amide catalyzed by immobilized penicillin amida se (EC 3.5.1.11) the product precipitates. The enzyme immobilized in t he support with the smallest pores could be reused without reduction i n the rate due to precipitation in the pores. This decreases the numbe r of immobilized enzyme molecules that can be used as biocatalysts. Th e latter was observed for supports with larger pores as the solubility decreases with increasing particle size. These results demonstrate th at biotransformations with insoluble substrates or products using free or immobilized enzymes can be easily carried out in aqueous two-phase systems, without organic solvents, provided that the pore sizes of th e supports are sufficiently small and that the rate of mass transfer f rom the precipitated substrate is targe. The latter increases with dec reasing particle size. (C) 1995 John Wiley and Sons, Inc.