title: C-22-substituted steroid derivatives as substrate analogues and inhibitors of cytochrome P-450scc.
abstract: Spectral and kinetic studies are reported for the effects of C-22-substituted steroids on purified bovine adrenocortical cytochrome P-450scc. The results are consistent with the recent proposal that the potency of 22-amino-23,24-bisnor-5-cholen-3 beta-ol as an inhibitor of the enzyme arises from a dual interaction, the binding of the steroid ring to the cholesterol site and bonding of the amine to the heme iron (Sheets, J.J., and Vickery, L.E., (1982) Proc. Natl. Acad. Sci. U.S.A. 79, 5773-5777). An analogue of the inhibitor with the 5,6 double bond reduced, 22-amino-23,24-bisnor-5 alpha-cholan-3 beta-ol, was synthesized by a similar procedure. A complex of this form with P-450scc produced a 422 nm Soret absorption maximum as found for the parent compound, indicating nitrogen coordination to the heme iron. A decrease in the spectral dissociation constant and inhibitory potency was also observed and is consistent with binding of the steroid ring to the cholesterol site on the enzyme. The 22-hydroxy analogue, 23,24-bisnor-5-cholene-3 beta,22-diol, was also prepared. This derivative produced a complex with P-450scc having a Soret peak at 417 nm as in the substrate-free form of the enzyme; the diol was also a competitive inhibitor, but exhibited decreased potency relative to the amine form. These results provide additional support for the role of amine coordination in producing the 422 nm species and in contributing to tight binding.
mesh_terms: D000302:Adrenal Cortex / Q000378:metabolism*; D000818:Animals; D002417:Cattle; D065607:Cytochrome P-450 Enzyme Inhibitors; D007700:Kinetics; D008928:Mitochondria / Q000378:metabolism*; D013053:Spectrophotometry; D013256:Steroids / Q000138:chemical synthesis / Q000494:pharmacology*; D013329:Structure-Activity Relationship
chemical_list: D065607:Cytochrome P-450 Enzyme Inhibitors; D013256:Steroids