Fruit tissue (4 g) was pulverized in a cold mortar and pestle with
4 ml potassium phosphate buffer (0.1 mol L1, pH 7.4) containing
1 mmol L1 EDTA and 2 mmol L1 DTT. The homogenate was
filtered through four layers of miracloth and centrifuged at
12,000 g for 10 min at 4 C. The supernatant was used for
assaying the SOD enzyme activity. Total SOD enzyme activity was
assayed photochemically (Monk, Fagerstedt, & Crawford, 1987;
Thayer, 1990). One unit of SOD was expressed as the amount of
enzyme, which produced a 50% inhibition of NBT reduction under
assay conditions.
2.7.3. Ascorbate peroxidase (