As is well known, the half-life (t1/2), which is the time required
for the enzyme activity to drop down to 50% of the starting value at
a given temperature, is an important economic parameter in many
industrial applications, because the higher its value, the higher the
enzyme thermostability. The kinetic results of these tests summarized
in Table 1 show that t1/2 progressively decreased and
the specific rate of first-order protease thermoinactivation (kd)
progressively increased with temperature, which means that its
irreversible denaturation became more and more significant. The
value of kd obtained at 55 ◦C (0.018 h−1) was significantly lower,
and that of t1/2 (37.64 h) higher, than those reported for proteases
from A. awamori (kd = 0.04 h−1; t1/2 = 17.1 h; T = 55 ◦C) [15] and A.
fumigatus (kd = 0.026 h−1; t1/2 = 1.08 h; T = 50 ◦C) [7]. Thus, the acid
protease produced in the current study appears to be more thermostable
than at least some of similar enzymes reported in the
literature.