Nd. Felicia et al., Characterization of cytochrome P450 2A4 and 2A5-catalyzed 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK) metabolism, ARCH BIOCH, 384(2), 2000, pp. 418-424
The tobacco-specific nitrosamine, 4-(methylnitrosamino)-1-(3-pyridyl)-1-but
anone (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 activ
ation by alpha -hydroxylation to exert its carcinogenic potential. The huma
n P450, 2A6 is a catalyst of this reaction. There are two closely related e
nzymes in the mouse, P450 2A4 and 2A5, which differ from each other by only
II amino acids. In the present study these two mouse P450s were expressed
in Spodoptera frugiperda (Sf9) cells using recombinant baculovirus. The cat
alysis of NNK metabolism by Sf9 microsomal fractions containing either P450
2A4 or 2A5 was determined. Both enzymes catalyzed the alpha -hydroxylation
of NNK but with strikingly different efficiencies and specificities. P450
2A5 preferentially catalyzed NNK methylhydroxylation, while P450 2A4 prefer
entially catalyzed methylene hydroxylation. The K-M and V-max for the forme
r were 1.5 muM 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 alpha -hydroxylation than is
the closely related human enzyme, P450 2A6. (C) 2000 Academic Press.