Characterization of cytochrome P450 2A4 and 2A5-catalyzed 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK) metabolism

Nadia D. Felicia, G. K. Rekha, Sharon E Murphy

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42 Scopus citations


The tobacco-specific nitrosamine, 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK), is a potent lung carcinogen in the A/J mouse, and is believed to be a causative agent for human lung cancer. NNK requires metabolic activation by α-hydroxylation to exert its carcinogenic potential. The human P450, 2A6 is a catalyst of this reaction. There are two closely related enzymes in the mouse, P450 2A4 and 2A5, which differ from each other by only 11 amino acids. In the present study these two mouse P450s were expressed in Spodoptera frugiperda (Sf9) cells using recombinant baculovirus. The catalysis of NNK metabolism by Sf9 microsomal fractions containing either P450 2A4 or 2A5 was determined. Both enzymes catalyzed the α-hydroxylation of NNK but with strikingly different efficiencies and specificities. P450 2A5 preferentially catalyzed NNK methyl hydroxylation, while P450 2A4 preferentially catalyzed methylene hydroxylation. The KM and Vmax for the former were 1.5 μM and 4.0 nmol/min/nmol P450, respectively, and for the latter 3.9 mM and 190 nmol/min/nmol P450. The mouse coumarin 7-hydroxylase, P450 2A5 is a significantly better catalyst of NNK α-hydroxylation than as the closely related human enzyme, P450 2A6.

Original languageEnglish (US)
Pages (from-to)418-424
Number of pages7
JournalArchives of Biochemistry and Biophysics
Issue number2
StatePublished - Dec 15 2000

Bibliographical note

Funding Information:
1This work was supported by a grant from the National Cancer Institute, CA-74913. 2To whom correspondence and reprint requests should be addressed. Fax: (612) 624-5135. E-mail: 3Abbreviations used: P450, cytochrome P450 enzyme; NNK, 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone; HPB, 4-(3-pyridyl)-1-butanone; OPB, 4-oxo-1-(3-pyridyl)1-butanone; OPBA, 4-oxo-4-(3-


  • Coumarin
  • Coumarin 7-hydroxylase
  • Cytochrome P450 2A4
  • Cytochrome P450 2A5
  • NNK


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