Solvent Effects on Stability

Organic solvents can interact with enzymes in several ways. There can be specific interactions between isolated solvent molecules and enzyme molecules. This kind of interaction also occurs in water containing dissolved solvent molecules. When a separate organic solvent phase is present, interfacial inactivation can also occur. This is sometimes called phase toxicity [55] to distinguish it from the molecular toxicity of isolated solvent molecules. Interfacial inactivation can be studied in detail by bubbling solvent through an aqueous enzyme solution under controlled conditions [56]. 

In most experimental studies of the influence of organic solvents on enzyme stability, the remaining catalytic activity after exposure to different solvents has been measured. In such a study it was found that the remaining activity of a 

Figu re 1.7 Activity retention of immobilized cells catalyzing an epoxidation reaction after exposure to organic solvents with different log P values. Data from Brink and Tramper [76] plotted according to Laane et al. [57]. Reprinted with permission of Wiley-Liss, a subsidiary of John Wiley and Sons, Inc. 

Large differences in sensitivity toward interfacial inactivation were observed between a-chymotrypsin and Candida rugosa lipase [56]. The lipase was most rapidly inactivated by 1-butanol and tolerated the hydrophobic hydrocarbons quite well, while the opposite was true for a-chymotrypsin. A detailed study of interfacial inactivation by 12 different solvents, all having log P values around 4, revealed 

In conclusion, most protein-dissolving solvents cause enzyme inactivation, and, among the other solvents, those having high log P values are less inactivating than others in many cases. However, the chemical nature of the solvents is certainly also of importance, and there are clearly large individual variations between different enzymes. 

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Table 2.2. Solvent Effect on Stability Constants (Ks = [ML]/[M][L]) of Complexes with Azacrowns Linked to Fluorophores...

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