Mössbauer and X-ray investigation of model compounds for the P460 center of hydroxylamine oxidoreductase from nitrosomonas

The divalent high-spin iron in the P460 center of hydroxylamine oxidoreductase and in three possible "picket fence" heme models exhibit extremely large quadrupole splittings (∼4 mms^-1). Their isomer shifts of about 1 mms^-1 are consistent with the X-ray results of two of the models, i.e. that Fe(II) is pentacoordinated. The coordination geometry of iron deviates considerably from the common fourfold symmetry of the "picket fence" porphyrin due to a CH₃CO₂^- ligand. This feature is also reflected by the significant anisotropies of g-factors, A tensor and rhombicity E/D.