Cytochrome P450 isozymes catalyzing 4-hydroxylation of parkinsonism-related compound 1,2,3,4-tetrahydroisoquinoline in rat liver microsomes

T. Suzuki, S. Fujita, S. Narimatsu, Y. Masubuchi, M. Tachibana, S. Ohta, M. Hirobe

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Microsomal 4-hydroxylase of 1,2,3,4-tetrahydroisoquinoline (TIQ), a possible candidate for causing Parkinson disease, was characterized by using rat hepatic microsomes and purified P450 isozymes. Kinetic analysis revealed that K(m) and V(max) values (mean ± SE) for hepatic microsomal TIQ 4-hydroxylase of male Wistar rats were 319.6 ± 26.8 μM and 12.13 ± 1.43 pmol·min-1·mg-1 protein, respectively. When TIQ 4-hydroxylase activity was compared in Wistar (an animal model of extensive debrisoquine metabolizers) and Dark Agouti (an animal model of poor debrisoquine metabolizers) rats, significant strain (Wistar>Dark Agouti) and sex (male>female) differences were observed. The microsomal activity toward TIQ 4-hydroxylation was increased by pretreatment of male Wistar rats with P448 inducers (β-naphthoflavone and sudan I), but not with phenobarbital. Pretreatment with propranolol, an inhibitor of P450 isozymes belonging to the P450 IID gene subfamily, decreased TIQ 4-hydroxylase activity. P450 BTL, a P450 isozyme belonging to the IID subfamily, showed TIQ 4-hydroxylase activity of 64.1 pmol·min-1·nmol P450-1, which was 3.2-fold that of microsomes (20.9 pmol·min-1·nmol P450-1). Antibody (IgG) against this isozyme suppressed microsomal TIQ 4-hydroxylase activity concentration-dependently. A male-specific P450 ml (P450IIC11) catalyzed this reaction to a much lesser extent (10.0 pmol·min-1·nmol P450-1), and its antibody did not affect the microsomal activity. These results suggest that TIQ 4-hydroxylation in hepatic microsomes are catalyzed predominantly by a P450 isozyme (or isozymes) belonging to the IID gene subfamily in non-treated rats and its immunochemically related P450 isozyme (or isozymes), and that a P450 isozyme (or isozymes) belonging to the IA subfamily also participates in TIQ 4-hydroxylation in rats pretreated with P448-inducers.

Original languageEnglish
Pages (from-to)771-776
Number of pages6
JournalFASEB Journal
Issue number2
Publication statusPublished - Jan 1 1992


  • Dark Agouti rat
  • Debrisoquine
  • Genotypic poor metabolizer
  • Metabolic polymorphism
  • P450 BTL
  • P450 m1
  • Phenotypic poor metabolizer
  • Rat liver microsomes

ASJC Scopus subject areas

  • Biotechnology
  • Biochemistry
  • Molecular Biology
  • Genetics


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