From the slopes of the straight lines of Fig. 3, an activation energy of the hydrolysis reaction (E*) of 19.03 kJ/mol and a standard enthalpy variation of enzyme unfolding (H◦U) of 90.35 kJ/molwere estimated with satisfactory correlation (R2= 0.908 and 0.988,respectively). The activation energy is lower than those of sim-ilar enzymes in water; for instance, E*values of 62, 36.8 and31.97 kJ/mol were reported for a neutral serine protease from A.fumigatus and an alkaline protease from Nacordiopsis alba, respectively. The very low E*value estimated for the proteaseunder investigation indicates that a few energy is required to formthe activated complex of azocasein hydrolysis, thus highlighting anespecially-effective hydrolytic capacity. Finally, the above compar-ison as a whole suggests that also its acidic nature may have playeda leading role from both viewpoints