A new monooxygenase product from 7-ethoxycoumarin and its relation to the O-dealkylation reaction

Biol Chem Hoppe Seyler. 1985 Jan;366(1):23-31. doi: 10.1515/bchm3.1985.366.1.23.


The widely used fluorometric microsomal monooxygenase test for 7-ethoxycoumarin O-dealkylation was reinvestigated with regard to other possible hydroxylation products. By HPLC-analysis no beta-hydroxylation of the ethyl group and no 8-hydroxylation could be detected. Only a small percentage of 6-hydroxylation occurred, but as a new major metabolite 7-ethoxy-3-hydroxycoumarin was found in quantities depending on the microsomal preparation used. The ratio of O-dealkylation to 3-hydroxylation varied according to species, induction, buffer and pH, suggesting that different isozymes of cytochrome P450 were involved. The isozyme mainly responsible for 3-hydroxylation exhibited a great dependence on cytochrome b5 as the donor for the second electron. The fluorometric test does not include 3-hydroxylation due to the virtual absence of an emission spectrum above 450 nm.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • 7-Alkoxycoumarin O-Dealkylase
  • Animals
  • Coumarins / metabolism*
  • Cytochrome b Group / biosynthesis
  • Cytochrome b Group / metabolism
  • Cytochromes b5
  • Enzyme Induction / drug effects
  • Hydroxylation
  • Isoenzymes / biosynthesis
  • Isoenzymes / metabolism
  • Mice
  • Microsomes, Liver / enzymology
  • Microsomes, Liver / metabolism
  • Mixed Function Oxygenases / biosynthesis
  • Mixed Function Oxygenases / metabolism*
  • NAD / metabolism
  • NADP / metabolism
  • Oxygenases / metabolism*
  • Phenobarbital / pharmacology
  • Rabbits
  • Rats
  • Rats, Inbred Strains
  • Species Specificity
  • Substrate Specificity
  • Swine
  • Time Factors


  • Coumarins
  • Cytochrome b Group
  • Isoenzymes
  • NAD
  • 7-ethoxycoumarin
  • NADP
  • Cytochromes b5
  • Mixed Function Oxygenases
  • Oxygenases
  • 7-Alkoxycoumarin O-Dealkylase
  • Phenobarbital