Study of enzyme-catalyzed reactions in organic solvents using multiple linear regression

We have used multiple linear regression to predict either initial rate, log initial rate or specificity for enzyme-catalyzed reactions performed in no n-aqueous solvents. The Subtilisin Carlsberg catalyzed transesterification of N-acetyl-L-phenylalanine ethyl ester by methanol. 1-propanol, and 1-buta nol was assayed in 30 non-aqueous solvents, and the lipase catalyzed transe sterification of methyl methacrylate in 23 non-aqueous solvents. Both sets of reactions were performed at fixed thermodynamic water activity. The lipa se catalyzed reactions were also performed in water saturated solvents and in dry solvents. The report illustrates that regression analysis may provid e insight into how solvents can alter the activity and specificity of enzym es suspended therein. A regression model for the subtilisin catalyzed react ion suggests that solvents which have a flat hydrophobic region inhibit by competing with the substrate for an enzyme cleft. Zn the lipase catalyzed r eaction, tetrachloroethylene is an outlier (i.e., behaves differently to ot her solvents) for all the regression models. This deviation, together with an element of structural similarity to the substrate, suggests that tetrach loroethylene acts as a competitive inhibitor. Log P is an important descrip tor and it, or an expression containing log P, appears in all the regressio n equations. Log initial rate is predicted by a two-descriptor model for ei ther enzyme system in solvents of high log P at fixed thermodynamic water a ctivity. Regression models with the same two descriptors predict initial ra te for the lipase system over the entire log P range for solvents maintaine d at fixed thermodynamic water activity and for dry solvents, but not for w ater saturated solvents. (C) 1999 Elsevier Science B.V. All rights reserved .