The activity of permeabilized cells of Escherichia coli strains during the biotransformation of trimethylamonium compounds, such as crotonobetaine and D-carnitine, into L-carnitine was determined. Permeabilization of cells did not affect the biotransformation of D-carnitine but improved the yield of L-carnitine obtained when crotonobetaine was used as biotransformation substrate (by nearly two-fold). A higher degree of cell activity with respect to control (45% yield) was observed with organic solvents such as acetone, ethanol, isopropyl alcohol and toluene (65-70% yield), detergents such as Triton X-100 and Tween 20 (70-75% yield) and polyethylenimine (80-89% yield). However, maximum cell activity was attained with 2% of the detergents, Triton X-100 and Tween 20, and 0.1% of polyethylenimine, using a temperature of 37 degrees C and 10-30min of treatment time, in which case a yield of 75-89% (100% increase) was obtained with E. coli 044 K74 and 85-94% (80% increase) with E. coli K38 T7-5KE32. Both detergents and polyethylenimine produced alterations in the outer membrane of treated cells since thin-sectioned bacteria were observed by transmision electron microscopy. NO L-carnitine dehydratase or carnitine racemase enzyme activity was detected within the extracellular medium when detergents and polyethyleneimine were used. Furthermore, transport studies showed that trimethyl ammonium compound carriers were not affected by permeabilization, while the rate of L-carnitime transport increased by 20%. (c) 2005 Elsevier Inc. All rights reserved.