Kinetic Experiments on the Binding of Metyrapone to Liver Microsomes

  • K. J. Netter
  • G.-F. Kahl
  • M. P. Magnussen


Kinetic experiments on the inhibition of oxidative microsomal O- and N-demethylations by metyrapone (2-methyl-1, 2-bis(3-pyridyl)-l-propanone, Su 4885) were carried out using mouse liver microsomes as the enzyme source. The model substrates were p-nitroanisole and N-monomethyl-p-nitroaniline. It was shown that the inhibition is competitive. The K i for metyrapone is 0.42 × 10−4 M and for the reduced metabolite of metyrapone 1.15×10−4 M. Their spectral dissooiation constants as determined from difference spectra have almost the same values. From this it is concluded that the degree of inhibition is correlated to the amount of metyrapone bound to cytochrome P-450. Metyrapone does not seem to displace naphthalene from its binding to cytochrome P-450. Assuming the simultaneous binding of substrate and inhibitor to different binding sites of the same enzyme, possible mechanisms for explaining competitive inhibition are discussed.


O-, N-demethylation Liver Microsomes Drug Metabolism Metyrapone Binding Kinetics 


O-, N-Demethylierung Lebermikrosomen Arzneimittelstoffwechsel Metyrapon Bindungskinetik 


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Copyright information

© Springer-Verlag Berlin Heidelberg 1969

Authors and Affiliations

  • K. J. Netter
    • 1
  • G.-F. Kahl
    • 1
  • M. P. Magnussen
    • 1
    • 2
  1. 1.Department of Pharmacology, Section of Chemical PharmacologyUniversity of MainzMainzGermany
  2. 2.Pharmakologisches Institut der UniversitätMainzDeutschland

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