Electromagnetic Properties of Hemoproteins III. ELECTRON PARAMAGNETIC RESONANCE CHARACTERISTICS OF IRON (III) AND MANGANESE (II) PROTOPORPHYRINS IX AND THEIR APOHEMOPROTEIN COMPLEXES IN HIGH SPIN STATES*

Manganese protoporphyrin IX was recombined with apoproteins of cytochrome c peroxidase, horseradish peroxidase, myoglobin, and hemoglobin to prepare artificial hemoproteins containing the manganese porphyrin in place of protoheme or iron protoporphyrin IX. Electron paramagnetic resonance (EPR) spectra of manganese (II) protoporphyrin IX and its apohemoprotein complexes were measured at Xand K-band frequencies in the temperature range from 42°K to 253°K and compared with those of the corresponding high spin iron (III) compounds. The ligand fields of these transition metal ions in 3d5 (S = S/2) ground states were found to have an essentially axial symmetry, in agreement with EPR studies of high spin ferric hemoproteins by Ingram and his associates. The axial ligand field of the manganese (II) ion in manganese protoporphyrin IX was further distorted rhombically upon binding to apohemoproteins. These axial and rhombic distortions of the ligand field symmetry of the manganese (II) ion were quantitatively estimated by determining zero field splitting parameters D and X from EPR characteristics. The combination of metalloporphyrins to apohemoproteins appeared to be an excellent method of achieving an ideal magnetic dilution of paramagnetic centers for EPR studies.