METABOLIC-ACTIVATION OF THE GENOTOXIC ENVIRONMENTAL CONTAMINANTS 2-NITROFLUORANTHENE AND 3-NITROFLUORANTHENE IN VARIANTS OF SALMONELLA-TYPHIMURIUM TA98

The mutagenic environmental pollutants 2-nitrofluoranthene (2-NFA) and 3-nitrofluoranthene (3-NFA), labelled with H-3 and C-14 respectively, were incubated with Salmonella typhimurium strain TA98, its nitroredu ctase-deficient variant TA98NR and its O-acetytransferase-deficient va riant TA98/1,8-DNP6, to investigate the activity of these metabolic pa thways under conditions approximating those of the Ames assay, hence t heir contribution to mutagenic potency, 2-Aminofluoranthene (2-AFA) wa s the major metabolite of 2-NFA (4 mu M) in all three TA98 variants, i solated by reverse-phase HPLC and identified by UV-vis and NMR spectro scopy and mass spectrometry, 2-AFA was formed more slowly in TA98NR (6 5 pmol/h/ml resting phase bacterial broth, 1 to 2x10(9) bacteria/ml) t han in TA98 (295 pmol/h/ml) or TA98/1,8-DNP6 (82 pmo/h/ml), 2-Acetamid ofluoranthene (2-AAFA) was also identified in incubations with TA98 (8 0 pmol/h/ml), TA98NR (21 pmol/ h/ml), and TA98/1,8-DNP6 (8 pmo/h/ml), 3-Aminofluoranthene (3-AFA, confirmed by UV-vis and NMR spectroscopy a nd mass spectrometry) was formed by all three variants from 3-NFA (4 m u M): TA98, 1.76 nmol/h/ml; TA98NR, 0.55 nmol/h/ml; TA98/1,8-DNP6, 2.9 3 nmol/h/ml, 3-Acetamidofluoranthene (3-AAFA) was not detected in any of the variants, 3-AFA and 3-AAFA were less mutagenic than 3-NFA, and required S9 for activation, Mutagenicity of 3-NFA relative to initial nitroreduction rate was similar in TA98 and in TA98NR, but almost 10-f old lower in TA98/ 1,8-DNP6; hence O-acetylation considerably enhances the mutagenicity of reduction products of 3-NFA, Mutagenicity of 2-NF A relative to initial nitroreduction rate was similar in TA98 and in T A98/1,8-DNP6; the bacterial genotoxicity of 2-NFA is therefore largely independent of O-acetyltransferase activity, Ratios of mutagenicity t o nitroreduction rate were similar in TA98 for 2-NFA and 3-NFA; differ ences in the potency of these isomers arise primarily from their respe ctive suitabilities as substrates for nitroreductase enzymes.