Standard CLEAs preparation using commercial preparations of lipases from Alcaligenes sp. (QL) and Candida antarctica (fraction B) (CAL-B) is not fully effective, some leakage of enzyme from the CLEA can be observed, and the SDS-PAGE of that preparations reveals that many enzyme molecules have not cross-linked properly. The co-precipitation of the lipases with poly-ethyleneimine (PEI) or PEI-sulfate dextran (DS) mixtures permitted to get fully physically stable CLEAs, with higher stability in the presence of organic solvents. Very interestingly, the conditions of precipitation and the nature of the polymers permitted to significantly alter the lipases activity, enantio-selectivity and specificity. For example, the QL showed changes in activity and enantio-selectivity in the hydrolysis of (+/-)-glycidyl butyrate when the derivative was prepared in presence or absence of Triton X-100. Results were further improved if the enzyme was co-precipitated with DS (from around 4 to more than 14). Similar changes in the lipase properties were found using CAL-B. (c) 2005 Elsevier Inc. All rights reserved.