Kinetic study of the thermal inactivation of cholinesterase enzymes immobilized in solid matrices.

The thermal inactivation of immobilized cholinesterase enzymes (ChE) in solid matrices where the protein unfolding is blocked was studied, thus enabling investigation of the kinetics of the inactivation process directly from the native structure to the inactivated state. The thermal inactivation of butyrylcholinesterase (BChE), recombinant human acetylcholinesterase (rHuAChE), and eel acetylcholinesterase (AChE) enzymes was studied in dry films composed of poly(vinyl pyrollidone) (PVP), bovine serum albumin (BSA) and trehalose at 60 degrees -120 degrees C. The kinetics follows a bi-exponential decay equation representing a combination of fast and slow processes. The activation enthalpy DeltaH(#) and the activation entropy DeltaS(#) for each of the three enzymes have been evaluated. The values of DeltaH(#) for the fast process and for the slow process of BChE are 33+/-3, and 28+/-2 kcal/mol, respectively, and the values of DeltaS(#) are 0.84+/-0.04, and -18.2+/-0.5 cal/deg, respectively. The appropriate value of DeltaH(#) for rHuAChE is 26+/-2 Kcal/mol, for both processes and the values of DeltaS(#) are -17.6+/-0.9, and -23.0+/-0.9 cal/deg, respectively. Similarly, the values of DeltaH(#) for eelAChE are 30+/-3, 31+/-1 kcal/mol, and the values of DeltaS(#) are -6.7+/-0.5, -9.1+/-0.2 cal/deg respectively.