Kinetic modelling of enzyme inactivation : kinetics of heat inactivation of the extracellular proteinase from Pseudomonas fluorescens 22F

The kinetics of heat inactivation of the extracellular proteinase from Pseudomonas fluorescens 22F was studied. It was established, by making use of kinetic modelling, that heat inactivation in the temperature range 35 - 70 °C was most likely caused by intermolecular autoproteolysis, where unfolded proteinase molecules are attacked by still active species. Kinetic modelling also showed that sodium caseinate acted as a competitive inhibitor against autoproteolysis. Autoproteolysis experiments gave indications for the dependence of the conformational stability of the proteinase on metal ions and pH.Although some mathematical models could describe the inactivation of the extracellular proteinase from Pseudomonas fluorescens 22F in the temperature range 80 - 120 °C, the mechanism of inactivation could not be precisely elucidated by making use of kinetic modelling. A model consisting of two consecutive irreversible reactions, possibly involving deamidation, where the first reaction would lead to a partially inactivated enzyme molecule with a specific activity of approximately 0.6, appeared to be in best accordance with the mechanism of inactivation. The inactivation behaviour was dependent on the sodium caseinate concentration and the pH, but not on the calcium ion activity.Kinetic modelling appeared to be a powerful method to predict enzyme inactivation as function of temperature and time. In combination with analytical methods, kinetic modelling may be a useful tool in the elucidation of the mechanism of enzyme inactivation