Semi-log plot of lnkd vs 1/T allowed estimating an activation
energy of protease denaturation (E*
d) of 314.12 kJ/mol (R2 = 0.946).
This value is one order of magnitude higher than those reported for
alkaline proteases from A. fumigatus (69 kJ/mol) [7], Nocardiopsis
alba (74.8 kJ/mol) [11] and Bacillus licheniformis (32.8–48.5 kJ/mol
depending on pH) [20], providing a further proof of the excellent
thermostability of A. foetidus protease, likely associated to its acidic
nature. One can also realize from this comparison that there is a
very large variability of E*
d data in the literature, likely due to large
differences in the source and purity of the enzymes as well as the
substrates used