Fig. 2 SOD inhibition curves using NBT (●) and XTT (○). The reaction mixture contained 2.5 ml of 50 mM carbonate buffer (B, pH 9.4; C, 10.2) or 50 mM phosphate buffer (A, pH 8.0) and 0.1 ml each of 3 mM EDTA, 3 mM xanthine, 56.1 mU/ml xanthine oxidase, 0.75 mM XTT or NBT, and sample solution containing SOD at the concentration shown at abscissa. In the NBT method, 0.1 ml of BSA was also added.