Relative mutagenicities of gaseous nitrogen oxides in the supF gene of pSP189

Carcinogenesis
D J KelmanA Dipple

Abstract

Gaseous nitric oxide (NO), an environmental pollutant found in cigarette smoke and diesel exhaust, has been shown to generate mutations in aerobic in vitro assays. The objective of this study was to identify which oxides of nitrogen, formed in the gaseous phase from NO, possess mutagenic activity. Samples of the plasmid pSP189, in 1 M HEPES buffer, pH 7.4, were exposed to preparations of nitrogen dioxide (NO2), dinitrogen trioxide (N2O3) or an air control. The gas mixtures were formed in a gas-tight syringe and were then introduced into 1 l flasks. The plasmid solution was introduced immediately afterwards. Transformation of Escherichia coli strain MBM7070 with the treated plasmids allowed analysis of mutation frequencies and the types of mutations induced in the target supF gene. The mutation frequency resulting from NO2 exposure was not different from that of the control. However, N2O3 produced a substantial number of mutations. The mutation frequency and the types of mutations were found to depend on the length of time that the gases were allowed to incubate in the syringe prior to introduction into the 1 l flasks (mutation frequency was maximal at approximately 2 min). The most prevalent mutations were AT-->GC transitions (...Continue Reading

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