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-b...