Metabolic activation of mutagenic N-hydroxyarylamines by O-acetyltransferase in Salmonella typhimurium TA98

Abstract

A new enzymatic activation of mutagenic N-hydroxyarylamines is described. An acetyl-CoA dependent enzyme that can activate 2-hydroxyamino-6-methyldipyrido[1,2- a: 3′,2′- d]imidazole ( N-OH-Glu-P-1) to a reactive species capable of binding to nucleic acid was found in a cell-free extract of Salmonella typhimurium TA98 but not in that of TA98/1,8-DNP 6, which shows low sensitivity to the mutagenic activity of N-OH-Glu-P-1. The enzyme was partially purified by streptomycin treatment, ammonium sulfate precipitation, DEAE-cellulose chromatography, and gel filtration chromatography of Sephadex G-150. Its molecular weight was estimated to be approximately 48,000. The directly mutagenic N-hydroxyarylamines, such as N-OH-Glu-P-1, 3-hydroxyamino-1-methyl-5 H-pyrido[4,3- b] indole ( N-OH-Trp-P-2), and N-hydroxy-2-aminofluorene ( N-OH-AF), were transformed to reactive derivatives by partially purified enzyme in the presence of acetyl-CoA. The K m value for acetyl-CoA was calculated to be 3.3 μ m. No acetyl residue, however, was incorporated into nucleic acid adducts. The enzymatic product of N-OH-Glu-P-1 bound most efficiently to polyguanylic acid among four polynucleotides. The enzyme did not show the N,O-acetyltransfer activity of N-hydroxyacetylaminofluorene ( N-OH-AAF). These results indicate that the enzymatic product of N-hydroxyarylamine is N-acetoxyarylamine, and that this enzyme can be called acetyl-CoA: N-hydroxyarylamine O-acetyltransferase. O-Acetyltransferase activity was inhibited by SH-blocking agents, several phenolic compounds, such as pentachlorophenol and 1-nitro-2-naphthol, and an antibiotic thiolactomycin. S. typhimurium mutation studies suggested that the O-acetyltransferase functions as an enzyme activating certain N-hydroxyarylamines within bacterial cells and is involved in the formation of mutants.