ESTERIFICATION REACTIONS CATALYZED BY LIPASES IN MICROEMULSIONS - THEROLE OF ENZYME LOCALIZATION IN RELATION TO ITS SELECTIVITY

The activity of lipases from Rhizopus delemar, Rhizopus arrhizus, and Penicillium simplicissimum entrapped in microemulsions formulated by b is-(2-ethylhexyl)sulfosuccinate sodium salt (AOT) in isooctane has bee n studied in esterification reactions of various aliphatic alcohols wi th fatty acids. The effect of the nature of the fatty acids (chain len gth) and of the alcohols (primary, secondary, or tertiary; chain lengt h; cyclic structures) on the lipase activities was investigated in rel ation to the reverse micellar structure. The lipases tested showed a s electivity regarding the structure of the substrates used when hosted in the AOT/isooctane microemulsion systems. Penicillium simplicissimum lipase showed higher reaction rates in the esterification of long cha in alcohols as well as secondary alcohols. Primary alcohols had a low reaction rate and tertiary a very slow rate of esterification. Long ch ain fatty acids were better catalyzed as compared to the shorter ones. Rhizopus delemar and R. arrhizus lipases showed a preference for the esterification of short chain primary alcohols, while the secondary al cohols had a low rate of esterification and the tertiary ones could no t be converted. The reaction of medium chain length fatty acids was al so better catalyzed than in the case of the long ones. The observed li pase selectivity appeared to be related to the localization of the enz yme molecule within the micellar microstructure due to the hydrophobic /hydrophilic character of the protein. The reverse micellar structural characteristics, as well as the localization of the enzyme, were exam ined by fluorescence quenching measurements and spectroscopical studie s.