Thermodynamic investigation of an alkaline protease from Aspergillus tamarii URM4634: A comparative approach between crude extract and purified enzyme

The thermostable crude proteolytic extract and purified protease produced by Aspergillus tamarii URM4634 were investigated at different temperatures. The activity results were used to estimate the activation energy of the hydrolysis reaction catalyzed by crude extract and purified protease (E* = 34.2 and 16.2 kJ/mol) as well as the respective standard enthalpy variations of reversible enzyme unfolding (DH°u= 31.9 and 13.9 kJ/mol). When temperature was raised from 50 to 80 °C in residual activity tests, the specific rate constant of crude proteolytic extract thermoinactivation increased from 0.0072 to 0.0378 min-1, while that of purified protease from 0.0099 to 0.0235 min-1. These values, corresponding to half-life decreases from 96.3 to 18.3 min and from 70.0 to 29.5 min, respectively, enabled us to estimate the activation energy (E*d= 49.7 and 28.8 kJ/mol), enthalpy (DH*d= 47.0 and 26.1 kJ/mol), entropy (DS*d= -141.3 and -203.1 J/mol K) and Gibbs free energy (92.6 < DG*d < 96.6 kJ/mol and 91.8 < DG*d < 98.0 kJ/mol) of thermoinactivation. Such values suggest that this protease, which proved to be highly thermostable in both forms, could be profitably exploited in industrial applications. To the best of our knowledge, this is the first comparative study on thermodynamic parameters of a serine protease produced by Aspergillus tamarii URM4634.