Cytochrome P-450 ligands: metyrapone revisited

Arch Biochem Biophys. 1985 Sep;241(2):397-402. doi: 10.1016/0003-9861(85)90562-4.


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.

Publication types

  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Animals
  • Cytochrome P-450 Enzyme System / analysis
  • Cytochrome P-450 Enzyme System / metabolism*
  • In Vitro Techniques
  • Ligands
  • Male
  • Metyrapone / metabolism*
  • Microsomes, Liver / enzymology
  • Phenobarbital / pharmacology
  • Rats
  • Rats, Inbred Strains


  • Ligands
  • Cytochrome P-450 Enzyme System
  • Phenobarbital
  • Metyrapone