The Arrhenius plot was graphed utilizing the activity values in
the temperature range of 20–80 C for enzyme. The activation
energy of the enzymatic reaction, calculated by the slopes of the plots of 6.5 kcal mol1K1 was obtained. In Table 3b, values of activation
free energy (DG#), activation enthalpy (DH#) and activation
entropy (DS#) for the catalytic reaction at different temperature
are reported. The negative value of activation entropy (DS#) indicates
that the structure of enzyme–substrate at transition state
was more ordered (Homaei, 2015b). The lower enthalpy value of
protease from L. vannamei showed that the formation of transition
state or activated complex between enzyme–substrate was very
efficient. Moreover, lower DG# value suggested that the conversion
of its transition complex into products was more spontaneous. The
feasibility and extent of a chemical reaction is best determined by
measuring the change in Gibbs free energy (DG#) for substrate
hydrolysis, i.e. the conversion of ES complex into products. The
lower the free energy change the more feasible the reaction, i.e.
the conversion of the reactant to product will be spontaneous.
The entropy was slightly lower, which explained that the transition
complex had lesser disorder. The free energy for activation of
substrate binding (DG#
E–S) and the free energy for the formation of
activation complex (DG#
E–T) were 1.54 and 0.52 kcal mol1,
respectively. The values of DG#
E–S and DG#
E–T again confirmed the
greater affinity of enzyme toward substrate for hydrolysis and its
spontaneous conversion into product.