Fig. 3 Time course of the reduction of NBT and XTT during the oxidation of glucose by glucose oxidase. The assay mixture (2.8 ml) contained the following components as the final concentration: 50 mM glycine-NaOH (pH 9.5), 0.1 mM glucose, and 0.1 mM NBT (●), 0.1 mM XTT (△) or 0.2 mM XTT (○). The reaction was initiated by the addition of glucose oxidase solution. The absorbance at 470 (XTT) or 560 nm (NBT) was monitored at 25℃.