Thermostability of modified enzymes: a detailed study

Three enzymes (lysozyme, EC 3.2.1.17; -chymotrypsin, EC 3.4.21.1; and Candi da rugosa lipase, EC 3.1.1.3) have been modified in order to alter their su rface hydrophobic/hydrophilic balance in opposite directions, by chemoenzym atic glycosylation and chemical binding of polyethylene glycol (PEG). The t hermal stability in aqueous environment of the produced biocatalysts was st udied, and two different approaches were considered: the determination of h alf-life times and the mechanistic analysis of the deactivation kinetics. T he comparison of half-life times indicated that an increase in enzyme surfa ce hydrophobic character induced a remarkable amelioration in thermostabili ty, while the increase in hydrophilic character produced the opposite effec t. However, the investigation of kinetic and thermodynamic parameters of en zyme deactivation revealed, in some cases, secondary stabilisation effects during some step of the mechanism, wh alpha ich would not have been detecte d if only half-life times had been considered. (C) 1999 Society of Chemical Industry.