Mechanisms of thermoinactivation of endoglucanase I from Trichoderma reesei QM 9414

The mechanism of irreversible thermoinactivation of endoglucanase I from Trichoderma reesei has been determined at 70 degrees C at the pH of maximum enzyme activity. The time-course of thermoinactivation did not follow first-order kinetics and kinetic constants of the process were dependent on enzyme concentration, suggesting that aggregation was the main process leading to irreversible inactivation. The enzyme was extremely resistant to urea, which in fact seemed to stabilize it against temperature. Disulphide exchange, deamidation and hydrolysis of peptide bonds were also responsible for the loss of enzyme activity at 70 degrees C.