Heme-linked properties of Pseudomonas cytochrome c peroxidase.  Evidence for non-equivalence of the hemes. 
Pseudomonas cytochrome c peroxidase contains two hemes, one of which is shown to be in low-spin and one in high-spin state.  The ferric enzyme reveals absorption maxima at 640 and 705 nm.  The alkaline transition of these bands indicates the sixth iron-binding ligand of the low-spin and high-spin heme to be, respectively, a methionyl residue and a water molecule.  The high-spin heme reacts with hydrogen peroxide to form a ferryl structure, which is the reactive intermediate in the peroxidatic reaction.  The ferrous enzyme binds carbon monoxide in a 1:1 molar ratio, whereas the ferric form is unreactive towards small anionic ligands like F- and CN-.  On this basis the peroxidase may also be classified as a cytochrome cc'.