Fig. 4.

H₂O₂ concentration of wild type and Δnpr in PIPES buffer.

Strains precultured overnight at 37°C were inoculated into fresh MRS medium at a final OD₆₀₀ of 0.05. The cells were used after static culture at 37°C for 5 hr. They were washed twice with PIPES buffer (pH 6.8) and resuspended in 10 mL H₂O₂ adjusted to 0 to 300 µM with PIPES buffer. After incubation at 37°C for 2 hr, the cells were harvested by centrifugation (10,000 g, 3 min). Twenty microliters of the supernatant was used for measuring the H₂O₂ concentration. After measuring the wavelength at 727 nm, the chromogenic reagent DA64 was used to quantify H₂O₂ based on the standard curve. The data are shown as the mean ± SE of three independent experiments.