Stability of a commercial lipase from Mucor javanicus: kinetic modelling of pH and temperature dependencies

The present communication reports experimental and modelling work pertaining to the independent roles of pH and temperature on deactivation of a crude lipase from Mucor javanicus. Experimental data of lipolytic activities were generated by a classic pH-stat assay on a triolein emulsion following incubation at several pH values for a fixed time, or at several temperatures for various times; postulated models were then fitted by nonlinear fitting to such data. The pH-dependence data were best fit by assumption of three forms of enzyme with increasing states of protonation, with pK(a) values of 6.2 and 11.3, respectively, where only the intermediate form is stable within the time frame considered. The thermal-dependence data were best fit by assumption of parallel steps of deactivation and rearrangement, with activation energies of 228.8 and 221.7 kJ mol^-1, respectively.