RELATIVE MUTAGENICITIES OF GASEOUS NITROGEN-OXIDES IN THE SUPF GENE OF PSP189

Gaseous nitric oxide (NO), an environmental pollutant found in cigaret te smoke and diesel exhaust, has been shown to generate mutations in a erobic in vitro assays. The objective of this study was to identify wh ich oxides of nitrogen, formed in the gaseous phase from NO, possess m utagenic activity. Samples of the plasmid pSP189, in 1 M HEPES buffer, pH 7.4, were exposed to preparations of nitrogen dioxide (NO2), dinit rogen 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 p lasmid solution was introduced immediately afterwards. Transformation of Escherichia coil strain MBM7070 with the treated plasmids allowed a nalysis of mutation frequencies and the types of mutations induced in the target supF gene. The mutation frequency resulting from NO2 exposu re was not different from that of the control. However, N2O3 produced a substantial number of mutations. The mutation frequency and the type s of mutations were found to depend on the length of time that the gas es were allowed to incubate in the syringe prior to introduction into the 1 l flasks (mutation frequency was maximal at approximate to-2 min ). The most prevalent mutations were AT-->GC transitions (68%), follow ed by GC-->AT transitions (30%), similar to previous findings when pur e NO was bubbled through pSP189 solutions. These results suggest that it is N2O3, rather than NO2, that is the most likely source of mutagen ic potential from gaseous nitrogen oxides.