1-Nitrosopyrene: an intermediate in the metabolic activation of 1-nitropyrene to a mutagen in Salmonella typhimurium TA1538

Incubation of Salmonella typhimurium TA1538, in suspension culture, with 1.5 or 23 microM 1-nitropyrene resulted in a time-dependent increase in reversions for up to 7 h. In contrast, when the bacteria were exposed to 1.5 microM 1-nitrosopyrene, a reduction product of 1-nitropyrene, maximum reversion induction occurred after 1 h and a much higher mutation frequency was detected. Examination of DNA isolated from Salmonella typhimurium incubated with 4.1 microM 4,5,9,10-3H]1-nitrosopyrene indicated the presence of one major adduct, N-(deoxyguanosin-8-yl)-1-aminopyrene, the same adduct observed previously when the bacteria were exposed to 1-nitropyrene. When calf thymus DNA was treated with 1-nitrosopyrene in the presence of ascorbic acid, 1-aminopyrene was formed concomitant with the production of N-(deoxyguanosin-8-yl)-1-aminopyrene. In the absence of ascorbic acid, a 20-fold reduction in DNA binding was observed and 1-aminopyrene was not detected. The observations that 1-nitrosopyrene forms the same DNA adduct and is more mutagenic than 1-nitropyrene, suggest that 1-nitrosopyrene is an intermediate in the mutagenic activation of 1-nitropyrene in Salmonella typhimurium TA1538. Since reduction of 1-nitrosopyrene was necessary to get appreciable DNA binding in vitro, further reduction of 1-nitrosopyrene to N-hydroxy-1-aminopyrene is probably required in the activation pathway.