Fig. 4.

Effect of exposure to oxygen on SAM cleavage activity and absorption spectra of PqqE-N. SAM cleavage activities of the as-purified (A) and reconstituted (B) PqqE-N were measured at 1–7 days of continuous mild exposure to O₂ (n = 6) and are shown with gray bars. Control samples (n = 3) kept under anaerobic conditions for the same period were also assayed and are shown with white bars. Activities at day 0 refer to the original activities before exposure to O₂. Absorption spectra of the as-purified (C) and reconstituted (D) PqqE-N (0.5 mg/ml) recorded at 1–7 days of the continuous exposure to O₂ (black to light gray dashed lines for the spectra at 1–7 days) are shown with those measured before the O₂-exposure (solid lines). Arrows indicate the direction of the spectral change. Insets: The absorbance value at 410 nm are plotted against time (in days).