title: Cytochrome P-450 for 11beta- and 18-hydroxylase activities of bovine adrenocortical mitochondria: one enzyme or two?
abstract: The 11beta- and 18-hydroxylase activities of a highly purified cytochrome P-450 from bovine adrenocortical mitochondria have been examined in detail with a view to determining whether the two activities are shown by a single protein or by two distinct proteins. The purified enzyme shows a single N-terminal residue (glutamic acid) and its amino acid composition is reported. Both enzyme activities decay considerably during storage at 4 degrees C for 11 days and the rates of decay are similar for the two activities. Metyrapone inhibits both activities competitively (Ki = 1.50 and 1.43 micrometer for 11beta- and 18-hydroxylase, respectively). Carbon monoxide inhibits both activities and the ratio CO:O2 for 50% inhibition is similar for the two activities (K = 1.69 and 1.53). A variety of nonspecific inhibitors produce approximately the same inhibition of both activities. Finally, antiserum produced by rabbits to the purified enzyme on double diffusion in agarose gels gives a single band with the purified enzyme. Increasing concentrations of antiserum added to the assay system produce increasing and proportionate inhibition of both activities. The evidence strongly supports earlier suggestions that the two hydroxylase activities occur in a single protein.
mesh_terms: D000302:Adrenal Cortex / Q000201:enzymology*; D000596:Amino Acids / Q000032:analysis; D000818:Animals; D002417:Cattle; D003577:Cytochrome P-450 Enzyme System / Q000378:metabolism*; D004355:Drug Stability; D005779:Immunodiffusion; D007700:Kinetics; D008797:Metyrapone / Q000494:pharmacology; D008928:Mitochondria / Q000201:enzymology*; D013252:Steroid 11-beta-Hydroxylase / Q000378:metabolism*; D013250:Steroid Hydroxylases / Q000378:metabolism*
chemical_list: D000596:Amino Acids; D003577:Cytochrome P-450 Enzyme System; D013250:Steroid Hydroxylases; D013252:Steroid 11-beta-Hydroxylase; D008797:Metyrapone