Kinetics and Thermodynamics of Thermal Inactivation of Cellulase from Salivary Glands of Macrotermes subhyalinus Little Soldier

For optimization of biochemical processes in food and pharmaceutical industries, the evaluation of enzyme inactivation kinetic models is necessary to allow their adequate use. kinetics and thermodynamic analysis of cellulase (GS-CX) from salivary glands of Macrotermes subhyalinus little soldier were studied, using carboxymethylcellulose as a substrate. Optimal conditions for enzymatic studies were determined to be pH 5.0 and 60 °C. Thermal inactivation of GS-CX was examined in more detail between 50 and 65 °C and in relation to exposure time. The investigation suggests the existence of a non-sensitive heat fraction on the enzyme structure, which is relatively stable up to temperatures close to 55 ºC. Denaturation of this enzyme, measured by loss in activity, could be described as a first-order model, with k-values between 0.0052 and 0.0337 min-1. D- and k-values decreased and increased, respectively, with increasing temperature, indicating faster cellulase (GS-CX) inactivation at higher temperatures. Results suggested that GS-CX is a relatively thermostable enzyme with a Z-value of 18.08 °C and Ea of 115.81 kJmol-1. The results of the thermodynamic investigations indicated that the hydrolytic reactions were: (1) not spontaneous (∆G > 0) and (2) slightly endothermic (∆H > 0). Positive values of entropy (ΔS > 0) for GS-CX indicated that this enzyme is found in a chaotic state at the end of the reaction. The high value obtained for the variation in enthalpy indicated that a high amount of energy was required to initiate denaturation, probably due to the molecular conformation of this enzymes. Results shown that the enzyme is quite stable for biotechnological applications.