Soybean lipoxygenase inactivation by pressure at subzero and elevated temperatures

Soybean lipoxygenase (LOX) inactivation [0.4 mg/mL in Tris-HCl buffer (0.01 M, pH 9)] was studied quantitatively under constant pressure (up to 650 MP a) and temperature (-15 to 68 degrees C) conditions and kinetically charact erized by rate constants, activation energies, and activation volumes. The irreversible LOX inactivation followed a first-order reaction at all pressu re-temperature combinations tested. In the entire pressure-temperature area studied, LOX inactivation rate constants increased with increasing pressur e at constant temperature. On the contrary, at constant pressure, the inact ivation rate constants showed a minimum around 30 degrees C and could be in creased by either a temperature increase or decrease. On the basis of the c alculated rate constants at 102 pressure-temperature combinations, an iso-r ate contour diagram was constructed as a function of pressure and temperatu re. The pressure-temperature dependence of the LOX inactivation rate consta nts was described successfully using a modified kinetic model of Hawley (Bi ochemistry 1971, 10, 2436-2442).