The Catalytic Performance of Pig Pancreas Lipase in Enantioselective Transesterification in Organic Solvents

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Abstract
Transesterification of vinyl acetate with racemic glycidol (R,S-2,3-epoxy-1-propanol) by pig pancreas lipase (PPL) was studied in hexane, diisopropylether, tetrachloromethane, and 2-butanone. Correction for substrate-solvent interactions was carried out by using thermodynamic activities of the substrates in the equations. Data from initial rate measurements could be fitted with a Ping Pong Bi Bi model, taking competitive inhibition by glycidol into account. Although plotting of the rates against thermodynamic activities resulted in similar curves for the various solvents, significant variation of the intrinsic parameters still remained. Similarity of the kinetic parameter values increased, however, when competitive inhibition by the solvents was taken into account, suggesting that simple interaction of the solvents with the active site occurs rather than exertion of specific effects on the catalytic properties of the enzyme. It appeared that the enantiomeric ratio, E, and the selectivity factor, α (the choice between vinyl acetate and (S)-glycidyl acetate), of PPL remained constant during the conversion in all solvents tested. Since E is a sensitive indicator for changes in the catalytic properties of an enzyme, this also confirms that the solvents have no specific effect on PPL. Seen in the light of reports concluding the opposite, the validity of generalization is discussed.