Recombinant Escherichia coli cells expressing penicillin G acylase (PGA) were permeabilized with organic solvents. Using the aromatic solvents, hexane or chloroform, increases of specific enzyme activity up to 380% were obtained, whereas acetone and pyridine reduced drastically activity and alcohols inactivated the enzyme. The type of solvent, physicochemical properties, solvent concentration and time of permeabilization were evaluated to obtain the optimal conditions to increase PGA activity by cell permeabilization. Solvents with lower dielectric constants (<5) and high hydrophobicity (log P > 2) were more effective in increasing PGA activity. (C) 2003 Elsevier Science Ltd. All rights reserved.