The active site of DpgC. (a) The model with dioxygen covered with 2Fo − Fc electron density contoured at 1.5σ (purple) and with Fo − Fc electron density (green positive and red negative contours), shown at 3σ and −3σ levels, phased by the final model at 2.4 Å in the original space group P21212. (b) The model with ozone at the active site. (c) The model with acetate at the active site. Note the disappearance of the difference electron density in (b) and (c) (same contouring as in a).