Modelling of the kinetics of thermal inactivation of glucoamylase from Aspergillus niger

Thermal inactivation of glucoamylase (GA) from Aspergillus niger was investigated by incubating the enzyme in buffer solutions in a broad temperature range. Preliminary experiments, made at different initial enzyme concentrations, showed the absence of association/aggregation reaction in the inactivation pathway. A biphasic character of inactivation was identified owing to the frequent sampling, conduction of experiments until the almost complete activity loss, and good accuracy of activity measurement. A further kinetic analysis showed that the biphasic inactivation could not be explained be the behaviour of different isozyme forms. The method of multitemperature evaluation was then applied to fit simultaneously all data with a model based on the Lumry–Eyring mechanism that incorporated the influence of temperature on the rate constants through the Arrhenius equation. A very close fit of activity values and good accuracies of the model parameters, the rate constants at the reference temperature of 60 °C and activation energies, validated the use of the model for the description of thermal inactivation of glucoamylase inactivation.