Figure 3. Prevention of the formation of compound II by NADPH at low concentrations.

The experimental conditions were similar to those of Table 1. With the additions at 15 min, the three reaction mixtures had a volume of 3.0 ml and comprised, at the final concentrations: in all three, 0.05 M phosphate buffer, pH 6.5, and catalase, 8.0 μM; in B and C, 1.6 μg·ml⁻¹ glucose oxidase; in A and C, 2 μM [¹⁴C]NADPH and the NADPH-regenerating system (1.0 mM G6P and 3.3 μg·ml⁻¹ yeast G6P dehydrogenase). After 15 min at 37 °C (arrow), 0.15 ml of water was added to reaction mixture A, and the generation of H₂O₂ was started at a rate of 180 nmol·ml⁻¹·h⁻¹ in reaction mixtures B and C by the addition of 0.15 ml of 100 mM glucose.