DO ORGANIC-SOLVENTS AFFECT THE CATALYTIC PROPERTIES OF LIPASE - INTRINSIC KINETIC-PARAMETERS OF LIPASES IN ESTER HYDROLYSIS AND FORMATION IN VARIOUS ORGANIC-SOLVENTS

When it is assumed that organic solvents do not interfere with the bin ding process nor with the catalytic mechanism, the contribution of sub strate-solvent interactions to enzyme kinetics can be accounted for by just replacing substrate concentrations in the equations by thermodyn amic activities. It appears from the transformation that only the affi nity parameters (K-m, k(sp)) are affected by this. Thus, in theory, th e values of these corrected, intrinsic parameters (K-m(int), k(sp)(int )) and the maximal rate (V-1) should be equal for all media. This was tested for hydrolysis, transesterification, and esterification reactio ns catalyzed by pig pancreas lipase and Pseudomonas cepacia lipase in various organic solvents. Correction was carried out via experimentall y determined activity coefficients for the substrates in these solvent s or, if not feasible, from values in data bases. However, although th e kinetic performances of each enzyme in the solvents became much more similar after correction, differences still remained. Analysis of the enzyme suspensions revealed massive particles, which explains the low activity of enzymes in organic solvents. However, no correlation was found between estimates of the amount of catalytically available enzym e (present at the surface of suspended particles or immobilized on bea ds) and the maximal rates observed. Moreover, the solvents had similar effects on the intrinsic parameters of suspended and immobilized enzy me. The possible causes for the effects of the solvents on the catalyt ic performance of the enzymes, remaining after correction for solvent- substrate interactions and the amount of participating enzyme, are dis cussed with respect to the premises on which the correction method is based. (C) 1995 John Wiley and Sons, Inc.