title: Electron paramagnetic resonance study of the high- and low-spin forms of cytochrome P-450 in liver and in liver microsomes from a methylcholanthrene-treated rabbit.
abstract: The high- and low-spin forms of cytochrome P-450 were observed by electron paramagnetic resonance (epr) in a liver slice and in hepatic microsomes from a rabbit injected with methylcholanthrene. Quantitation of the epr absorption of these two chemical species and comparison with a preparation from a control rabbit showed that the single injection of drug increased the concentration of cytochrome P-450 to more than ten times its control value. Analysis of the epr spectrum for the high-spin compound showed that it is the most rhombically distorted ferric heme iron site yet observed (E/D = 0.10). It is suggested that microsomal cytochrome P-450 can exist in two interconvertible forms, in which the heme iron can either be high-spin or low-spin, depending upon the nature of the nonporphyrin ligands of the metal. There seems to be no need to postulate the existence of two different cytochrome P-450 proteins.
mesh_terms: D000311:Adrenal Glands / Q000166:cytology; D000818:Animals; D002417:Cattle; D003580:Cytochromes; D004578:Electron Spin Resonance Spectroscopy; D007501:Iron; D008099:Liver / Q000032:analysis / Q000187:drug effects; D008297:Male; D008748:Methylcholanthrene / Q000494:pharmacology; D008862:Microsomes, Liver / Q000032:analysis; D008928:Mitochondria; D010634:Phenobarbital / Q000494:pharmacology; D011549:Pseudomonas; D011817:Rabbits; D051381:Rats
chemical_list: D003580:Cytochromes; D008748:Methylcholanthrene; D007501:Iron; D010634:Phenobarbital