The SOD activity of hemocytes was measured by its inhibition of
superoxide radical-dependent reactions using a Ransod kit (Randox, Crumlin, UK) [27]. Briefly, the reaction mixture (1.7 mL) contained 0.05 mM xanthine and 0.025 mM 2-(4-iodophenyl)-3-(4-
nitrophenol)-5-phenyltetrazolium chloride (INT) dissolved in
50 mM CAPS (pH 10.2) and 0.94 mM EDTA. In the presence of 250 ml
of 80 U L1 xanthine oxidase (XO), superoxide and uric acid were
produced from the xanthine. The superoxide radical then reacted
with INT to produce a red formazan dye. The OD was measured at
505 nm and 37 C, and the rate of the reaction was estimated from
the absorbance readings 0.5 and 3 min after adding XO. A reference
standard (SOD) was supplied with the Ransod kit. The specific
activity was expressed as SOD U (g protein) 1.