Lipase from Pseudomonas fluorescens (PFL) has been immobilized by using different immobilization protocols. The catalytic behavior of the different PFL derivatives in the hydrolytic resolution of f'ully soluble (R,S) 2-hydroxy l-phenyl butanoic acid ethyl ester (HPBE) in aqueous medium was analyzed. The soluble enzyme showed a significant but low enantioselectivity, hydrolyzing the S isomer more rapidly than the R-isomer (E = 7). The enzyme, immobilized via a limited attachment to a long and flexible spacer arm, showed almost identical activity and specificity to the soluble enzyme. However, other derivatives, e.g. PFL adsorbed on supports covered by hydrophobic moieties (octyl, decaoctyl), exhibited significant hyperactivation on immobilization (approximately 7-fold). Simultaneously, the enantioselectivity of the PFL-immobilized enzyme was significantly improved (from E = 7 to E = 80). By using such derivatives, almost pure R eater isomer (e.e. > 99%) has been obtained after 55% hydrolysis of the racemic mixture of a solution of 10% (w/v) (R,S) HPBE. The derivatives could be used for 10 cycles without any significant decrease in the activity of the biocatalyst. (C) 2001 Elsevier Science Inc. All rights reserved.