Fig. 2. Heme synthase activity of wt AhbD and the AhbD variants. The tetrapyrrole content in the assay mixtures was analyzed after 24 h of incubation at 17 °C by HPLC. The elution of the tetrapyrroles was monitored by measuring the absorption at 400 nm (solid line) and the fluorescence (dotted line, excitation at 409 nm, emission at 630 nm). Fe-COPRO III eluted at 20.9 min, the potential monovinyl intermediate at 30.1 min and heme at 37.5 min.