REDUCTIVE METABOLISM OF 1-NITROPYRENE ACCOMPANIES DEAMINATION OF CYTOSINE

1-Nitropyrene (1-NP), a common environmental pollutant, is a mutagen a nd tumorigen. Nitroreduction is a major pathway by which 1-NP is metab olized. In order to study the mutational specificity of reductively ac tivated 1-NP, single-stranded M13mp18 DNA was treated with tritium-lab eled 1-nitrosopyrene in the presence of ascorbic acid to generate N-hy droxyl-aminopyrene in situ. HPLC analysis of the treated DNA, followin g enzymatic digestion, showed that >95% of tritium was located in one major adduct, N-(deoxyguanosin-8-yl)-1-aminopyrene. Transfection of th ese adducted M13 DNA in Escherichia coli indicated a dose-dependent re duction in viability with concomitant enhancement in mutagenesis in th e lacZ gene fragment. Without SOS functions, the major type of mutatio n was C-->T transition (48%). Further studies have shown that cytosine deamination occurred during ascorbic acid-induced nitroreduction, whi ch was likely responsible for the C-->T transitions. Deamination of cy tosine alco occurred at a significant frequency when nitroreduction of either 1-NP or 1-nitrosopyrene was catalyzed by xanthine oxidase, a m ammalian nitroreductase.