Separation and thermal characterization of ionically and tightly cell-wall-bound pectin methylesterase from cucumbers (Cucumis sativus)

Thermal characteristics of cell-wall-bound pectin methylesterase (PME) from cucumbers were determined. Heat inactivation of PME followed first-order r eaction kinetics. Biphasic inactivation curves indicated the presence of he at-labile and heat-stable fractions. Inactivation of PME accelerated above 65 degrees C. The z values between 70 degrees C and 80 degrees C were 7.6 d egrees C and 9.0 degrees C for heat-stable fractions of ionically (IPME) an d tightly cell wall bound PME (TPME), respectively. Temperature optima for the initial activities of IPME and TPME were 65 degrees C and 60 degrees C, respectively. However, for longer periods of activity determination, both IPME and TPME showed a temperature optimum at 50 degrees C. The E-a values for initial activities were 5 kcal mol(-1) (20-65 degrees C) and 7.2 kcal m ol(-1) (20-60 degrees C) for IPME and TPME, respectively.