THERMAL DEACTIVATION KINETICS OF CM-CELLULASE FROM A LOCAL ISOLATE OF ASPERGILLUS-NIGER (RD-2231)

The kinetic of thermal deactivation of CMC-ase activity of A. niger, locally isolated, was studied. The enzyme was found to be more stable in temperatures below 40-degrees-C. The rates of activity decay were significant at high temperatures and can be described as a first-order kinetic model. Deactivation rate constants (K(d)) were determined at different temperatures (30, 40, 55 and 65-degrees-C). K(d) value for CMC-ase activity decay at 65-degrees-C was 28 times higher than its value at 30-degrees-C. An Arrhenius type temperature dependence of K(d) was found, and the activation energy (E(a)) of the thermal deactivation was calculated to be 8400 cal/mole. Thermodynamic quantities (DELTAH) and (DELTAS) for deactivation process were 7700 and 11.9 cal/mole, respectively. The change of two kinetic parameters, i.e. V(max) and K(m) under deactivation conditions, was discussed.