The Formation of g=2.49-Species of Cytochrome P450 in the Rat Liver by PCB126 Oral Administration: Identification of Heme Axial Ligands by EPR Spectroscopy

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Rat livers and microsomes were subjected to electron paramagnetic resonance (EPR) measurements at 77 K. The EPR spectra of the livers from the control group, carbon tetrachloride-, 3-methylcholanthrene-, and 3,3′,4,4′,5-pentachlorobiphenyl (PCB126)-treated rats exhibited an EPR spectrum at g=2.40, 2.24, and 1.93, which is characteristic of P450 in a resting state. The liver of the PCB126-treated rats showed an additional distinct EPR spectrum at g=2.49, 2.26, and 1.87 (g=2.49-species). The heme environmental structure of g=2.49-species was identified by crystal field analysis using three EPR g-values of the microsome treated with various chemicals. These results indicated that g=2.49-species is a hemeprotein with cysteine thiolate at the 5th coordination site, and a nitrogenous ligand at the 6th site.