Thermal stabilities of peroxidases from fresh pinto beans

Heat stabilities of crude and partially purified soluble (SPOX), ionically bound (IPOX) and total peroxidase (TPOX) from fresh pinto beans were investigated at 55-90 degrees C, Heat inactivation of peroxidase (POX) followed first-order reaction kinetics. Each inactivation curve consisted of two linear parts: initial rapid inactivation (heat-labile) followed by slower inactivation (heat-stable). IPOX showed activation during heat treatment with a highly heat-stable isoenzyme (D-90=40 min) which was more heat-stable than SPOX. Activation energies for heat-stable parts of crude IPOX and SPOX were, respectively, 12.1 and 36.4 kcal.mol-1 with z values 45.4 and 14.1C degrees. Heat stable SPOX isoenzymes (D-70=22.6) were obtained by 65-95% (NH4)(2)SO4 precipitation from crude SPOX. Two POX fractions (F1 and F2) were separated from TPOX by ion-exchange chromatography.