ANALYSIS OF THE MECHANISM AND KINETICS OF THERMAL INACTIVATION OF ENZYMES - CRITICAL-ASSESSMENT OF ISOTHERMAL INACTIVATION EXPERIMENTS

The study deals with information obtained from conventional isothermal inactivation experiments. When the lumped character of enzyme activit y was analysed, identical activity-time profiles could be obtained fro m several mechanisms when the number of equivalent mechanisms increase d exponentially with the number of parameters in the corresponding kin etic equations. The assessment of isothermal evaluation of inactivatio n kinetics was demonstrated using selected experiments from the litera ture exhibiting a deviation from first-order kinetics. Experiments wer e classified, according to the shape of the inactivation curve, into b iphasic, grace-period and activation-period inactivations. A unified e valuation procedure, based on the discrimination among a few kinetic m odels derived from a general unimolecular series mechanism, was employ ed for all experiments. It was shown that regardless of the shape of t he inactivation curve, only a few experiments needed more than a simpl e series mechanism represented by a biexponential curve, for a satisfa ctory fit. Carrying out inactivation experiments at several temperatur es was shown to be very effective in checking the consistency of kinet ic equations obtained by isothermal evaluation. The results of isother mal evaluation could always be questioned in this way and no consequen t conclusions on inactivation mechanism could be drawn. Copyright (C) 1996 Elsevier Science Ltd.