Figure 12.

Model describing the redox-dependence of heme binding to the HRMs of HO2. In Fe³⁺-HO2°, the thiolate of Cys265 is sequestered in a disulfide bond and is unavailable to ligate heme. However, upon reduction of the disulfide bond in Fe³⁺-HO2^R, the free thiolate is available to bind to heme. Further studies are required to discriminate between binding of Cys265 to heme in the catalytic core or directly to a second heme in the HRM. However, as discussed in the manuscript, we favor the latter scenario.