THERMAL INACTIVATION KINETICS OF WHEAT-GERM LIPOXYGENASE

Thermal inactivation curves for wheat germ lipoxygenase (LPO) in parti ally purified and crude extracts were determined in capillary tubes at 60-68-degrees-C. The biphasic curves fitted a two-fraction first orde r model suggesting the presence of 2 groups of isozymes. At 60-degrees -C, the inactivation rate constants were 9.112 x 10(-5) sec-1 and 9.17 4 x 10(-6) sec-1 respectively, for thermolabile phase I and thermostab le phase II in the partially purified extract, a difference of one ord er of magnitude. For the temperature change from 60 to 68-degrees-C, t he rate constants increased by three orders of magnitude, implying a v ery high sensitivity (for LPO inactivation in partially purified extra ct DELTAH(double dagger) = 646261 J.mole-1, DELTAS(double dagger) = 16 19 J.mole-1.K-1 for phase I, DELTAH(double dagger) = 546099 J.mole-1, DELTAS(double dagger) = 1298 J.mole-1.K-1 for phase II) to heat by bot h phases, although phase I was clearly the least stable.