The Accuracy of E-value Determinations

Since the substrates for which organic solvents are attractive media normally have lower activity coefficients in organic solvents than in water, the KM-values determined from plots of rate vs. substrate concentration will generally be higher in organic media. The validity of this approach has been ascertained for several systems [81, 86]. 

When this reasoning is applied to enantioselective enzymatic reactions, it follows that the ratio of specificity constants should not be affected by a change of medium that leads to different (but of course identical for the two enantiomers) values for the substrate activity coefficients. Indeed, solvent effects were not observed for, 

The investigation by Wolff and coworkers into the solvent effects of the enantioselectivity of chymotrypsin-catalyzed hydrolyses [87] raises another question. The research aimed at corroborating the results reported by Jones and Mehes [91] on 

Finally, the purity-related performance of the enzyme preparation would appear to be a constant throughout a series of measurements. This, however, may not be the case when several enzyme species are present and different activities are expressed as a function of the medium composition [100]. Although it would appear that this source of error is abolished by the present-day availability of highly pure enzyme preparations (but see also [101, 102]), the intrinsic properties of i.e. Upases may lead to different E-values as a result of interfacial activation [103] and the conformation of the lid structure of lipases [56]. 

In summary, it may well be that a substantial number of cases where effects of solvent on the enantioselectivity have been reported are erroneous rather than 

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