title: Inhibition of adrenocortical cytochrome P-450scc by (20R)-20-phenyl-5-pregnene-3 beta,20-diol.
abstract: The effects of the cholesterol analogue, (20R)-20-phenyl-5-pregnene-3 beta,20-diol (20-PPD), on the catalytic and spectral properties of purified bovine adrenocortical cytochrome P-450scc were investigated. In contrast to results with cholesterol and (20R)-20-hydroxycholesterol, no conversion of 20-PPD to pregnenolone could be detected; instead, 20-PPD was found to be a potent inhibitor of cytochrome P-450scc. Kinetic analyses showed that the inhibition is reversible and competitive with respect to cholesterol with an apparent Ki = 30nM. Spectral binding studies with ferricytochrome P-450scc showed that 20-PPD formed a 1:1 complex with the enzyme, having an absorption spectrum similar to that produced by (20R)-20-hydroxycholesterol. These results indicate that 20-PPD binds with very high affinity to the substrate site on cytochrome P-450scc. The finding that the phenyl side chain is readily accommodated suggests the presence in this site of an open pocket which may be normally occupied by C-22 to C-27 of the cholesterol side chain.
mesh_terms: D000302:Adrenal Cortex / Q000378:metabolism*; D000818:Animals; D001665:Binding Sites; D002417:Cattle; D002786:Cholesterol Side-Chain Cleavage Enzyme / Q000037:antagonists & inhibitors; D065607:Cytochrome P-450 Enzyme Inhibitors; D007700:Kinetics; D008928:Mitochondria / Q000378:metabolism; D008958:Models, Molecular; D011283:Pregnenes / Q000494:pharmacology*; D011487:Protein Conformation; D013053:Spectrophotometry
chemical_list: C012486:20-phenyl-5-pregnene-3 beta,20-diol; D065607:Cytochrome P-450 Enzyme Inhibitors; D011283:Pregnenes; D002786:Cholesterol Side-Chain Cleavage Enzyme