Fig. 5 SOD inhibition curves using the WST-1 (●) and WST-8 (○) systems. The reaction mixture contained 2.5 ml of a phosphate buffer (A, pH 8.0) or 50 mM carbonate buffer (B, pH 9.4; C, pH 10.2) and 0.1 ml of 3 mM EDTA, 3 mM xanthine, 58 mU/ml of xanthine oxidase, 0.75 mM WST and the sample solution containing SOD at the concentration shown on the abscissa.