THE CATALYTIC PERFORMANCE OF PIG PANCREAS LIPASE IN ENANTIOSELECTIVE TRANSESTERIFICATION IN ORGANIC-SOLVENTS

Transesterification of vinyl acetate with racemic glycidol (R,S-2,3-ep oxy-1-propanol) by pig pancreas lipase (PPL) was studied in hexane, di isopropylether, tetrachloromethane, and 2-butanone. Correction for sub strate-solvent interactions was carried out by using thermodynamic act ivities of the substrates in the equations. Data from initial rate mea surements could be fitted with a Ping Pong Bi Pi model, taking competi tive inhibition by glycidol into account. Although plotting of the rat es against thermodynamic activities resulted in similar curves for the various solvents, significant variation of the intrinsic parameters s till remained. Similarity of the kinetic parameter values increased, h owever, when competitive inhibition by the solvents was taken into acc ount, suggesting that simple interaction of the solvents with the acti ve site occurs rather than exertion of specific effects on the catalyt ic properties of the enzyme. It appeared that the enantiomeric ratio, E, and the selectivity factor, alpha (the choice between vinyl acetate and (S)-glycidyl acetate), of PPL remained constant during the conver sion in all solvents tested. Since E is a sensitive indicator for chan ges in the catalytic properties of an enzyme, this also confirms that the solvents have no specific effect on PPL. Seen in the light of repo rts concluding the opposite, the validity of generalization is discuss ed.