DESCRIPTION OF HYDROLASE-ENANTIOSELECTIVITY MUST BE BASED ON THE ACTUAL KINETIC MECHANISM - ANALYSIS OF THE KINETIC RESOLUTION OF GLYCIDYL (2,3-EPOXY-1-PROPYL) BUTYRATE BY PIG PANCREAS LIPASE

The kinetic resolution of R,S-glycidyl (R,S-2,3-epoxy-1-propyl) butyra te catalyzed by pig pancreas lipase (PPL) was studied in monophasic an d biphasic systems. The course of the resolution at ester concentratio ns exceeding 0.05 M or in the presence of R,S-glycidol (R,S-2,3-epoxy- 1-propanol), could not be described by the equations derived for a one substrate enzyme with a minimal kinetic scheme (Chen el al., 1987). T rivial causes like heterogeneity in activity of the (crude) PPL prepar ation and equilibrium phenomena due to changing phase ratios could be excluded. An equation based on the kinetic mechanism of hydrolases, in which the acyl-enzyme intermediate is allowed to react with water as well as with the produced alcohol (quantified by the selectivity const ant, alpha), was evaluated. All initial rate and conversion data could be adequately fitted with this equation, not only for PPL in the mono phasic (free in solution) but also in the biphasic (adsorbed to the in terface) systems where it exhibited better activity and enantioselecti vity. Thus, the enantiomeric ratio (E) and alpha are intrinsic paramet ers of PPL, remaining constant during the course of the reaction. The correctness of the approach for the PPL-system indicates that descript ion of enantioselectivity must be based on the actual kinetic mechanis m of hydrolases.