Superoxide Dismutase (EC:1.15.1.1)

Superoxide dismutase activity was determined according to Giannopolitis and Ries (1977). The reaction was conducted in a reaction chamber under illumination with a 15-W fluorescent lightbulb at 25°C after adding 2 mL of 50 mM potassium phosphate buffer pH 7.8, 250 μL of 13 mM methionine, 200 μL of 75 mM nitroblue tetrazolium (NBT), 200 μL of 0.1 mM EDTA and 250 μL of 2 μM riboflavin to 50 μL of protein extract. The tubes were vortexed and placed inside the chamber (total absence of ambient light) for 15 min top permit the formation of the blue formazan compound by photoreaction of NBT. A control was prepared for each sample using the same conditions, except that the tubes were covered with aluminum foil to prevent light exposure. After 15 min, the reactions were vortexed, and readings were obtained in a spectrophotometer at a wavelength of 560 nm. The results were expressed as U (unit) SOD mg^–1 protein.