title: Cytochrome P-450 ligands: metyrapone revisited.
abstract: Expressing metyrapone interactions with ferrous cytochrome P-450 as ligand saturation by cytochrome, rather than the more conventional cytochrome saturation by ligand, an extinction coefficient of 68.5 +/- 1.8 mM-1 cm-1 for the metyrapone complex of dithionite-reduced rat hepatic microsomal cytochrome P-450 was derived. Utilizing this new extinction coefficient, the increased cytochrome P-450 present after phenobarbital induction was almost exclusively that which is able to both bind to metyrapone and form a metabolic-intermediate complex from norbenzphetamine. However, it was not the only subpopulation present in microsomes that was able to bind metyrapone, nor the only one capable of forming a metabolic intermediate complex from norbenzphetamine. Thus, neither technique alone can be used to quantitate the "phenobarbital-induced form" of cytochrome P-450.
mesh_terms: D000818:Animals; D003577:Cytochrome P-450 Enzyme System / Q000032:analysis / Q000378:metabolism*; D066298:In Vitro Techniques; D008024:Ligands; D008297:Male; D008797:Metyrapone / Q000378:metabolism*; D008862:Microsomes, Liver / Q000201:enzymology; D010634:Phenobarbital / Q000494:pharmacology; D051381:Rats; D011919:Rats, Inbred Strains
chemical_list: D008024:Ligands; D003577:Cytochrome P-450 Enzyme System; D010634:Phenobarbital; D008797:Metyrapone