Diheme cytochrome c-554 from Nitrosomonas. Soret resonance Raman indication of an unusual ferric 5-coordinate structure.

The diheme cytochrome c-554 which participates in ammonia oxidation in the chemoautotroph , Nitrosomonas europaea has been studied by Soret excitation resonance Raman spectroscopy. The Raman spectrum of reduced cytochrome c-554 at neutral pH is similar classical 6-coordinate low-spin ferrous mammalian cytochrome c. In contrast, the spectrum of ferric cytochrome c-554 suggests a 5-coordinate state which is unusual for c hemes. The oxidized spectrum closely resemble that of horseradish peroxidase (HRP) or cytochrome c peroxidase (CcP) at pH 6.4. The narrow linewidth of the heme core-size vibrations indicates that both heme irons of c-554 have similar geometries.