Purification and some properties of catalase from wheat germ (Triticum aestivum L.)

Two isoforms of catalase, CAT-1 and CAT-2, were purified from wheat germ after extraction, ammonium sulfate precipitations, hydrophobic chromatography, and two ionic-exchange chromatographies. The global yields and the purification factors were close to 3% and 50 for CAT-1 and close to 6% and 100 for CAT-2. Both isoforms exhibit an optimum activity at pH 7. When pH was decreased from 7 to 5.6, CAT-1 showed a decreasing affinity for its substrate, whereas the opposite was found for CAT-2. Both isoforms were irreversibly denaturated when exposed to acidic pH, CAT-1 being more sensitive than CAT-2. Conversely, CAT-2 appeared to be more sensitive to inhibitors. The rate as well as the extent of denaturation during incubation with 3-amino-1,2,4-triazole (AT) were higher with CAT-2 than with CAT-1. Guaiacol is a competitive inhibitor more potent with respect to CAT-2. The difference in affinity for hydrogen peroxide as well as the poor stability of CAT-1 in acidic medium suggests that this isoform could be less effective during dough mixing.