Figure 2.

Characterization of the H45W/G159W variant of HO2. The absorbance spectrum of TCEP-reduced H45W/G159W HO2_sol^R incubated with Fe³⁺-heme and separated from unbound heme is shown in red. The spectrum is of 5 μm protein in 50 mm Tris (pH 8.0), 50 mm KCl buffer at 20 °C. For comparison, the spectra of WT HO2_tail, which binds heme at both the Cys²⁶⁵/His²⁵⁶ (HRM1) and Cys²⁸² (HRM2) sites (solid black), and WT HO2_sol^O, which binds heme at the core with His⁴⁵ (dashed black), are shown.