Role of metabolic activation in azide mutagenesis

242 160 Nilan, R.A., and A. Kleinhofs, Program in Genetics and Department of Agron o m y and Soils, Washington State University, Pullman, Wash. 99164 (U.S.A.) Role o f metabolic activation in azide mutagenesis Azide, as the sodium or potassium salt, is a c o m m o n environmental chemical used extensively in agriculture, biochemistry, industrial chemistry, and clinical work. Azide is also a potent mutagen in plants and bacteria. We have demonstrated that azide (1) induces only base-substitution mutations, (2) is not mutagenic to DNA in vitro, (3) acts only in metabolically active cells, (4) may act only during DNA replication, (5) is most effective in UV excision-repair deficient strains in bacteria, (6) requires recombination to fix the azide-induced DNA lesions as mutations, and (7) does not break chromosomes in plants and human leukocytes. Azide has been reported to be non-carcinogenic in rats. Our previous work with this chemical indicates that metabolic activation plays an important role in its function as a mutagen. We have developed a sensitive bacterial bioassay using Salmonella typhimurium strain TA1530 to detect azide by its mutagenic action. Using this assay we have determined that azide is rapidly taken up by barley embryos, but is practically impossible to remove by washing. This suggests that a mutagenic metabolic product of azide rather than azide per se exists in the barley embryos. Research is in progress to isolate and identify this presumed mutagenic metabolite of azide. Although azide per se may not be carcinogenic in rats, the potential for its activation to a mutagenic and/or a carcinogenic molecule by plant or microbial metabolic systems deserves careful evaluation. (Supported by the U.S.A. ERDA Contract E[451]-2221.)

161 Nishioka, H., Doshisha University, Kyoto (Japan) Super-sensitive DNA-repair test-liquid for confirming DNA-damagicity of mutagens Super-sensitive DNA-repair test-liquid was recently developed by us for the purpose of confirming DNA-damagicity of mutagens. E. coli strains, WP2 (trp-, uvrA ÷, recA ÷) and WP100 (trp-, uvrA-, recA-) are incubated overnight in minimal medium supplemented with a requiring amino acid. An 0.1-ml aliquot of each culture diluted appropriately is added to a test tube containing 1.8 ml minimal medium with the amino acid and 0.1 ml of different concentrations of a drug to be tested. An optical density at 660 nm of the culture treated with the drug for 6-h incubation at 37°C with shaking is measured with a spectrophotometer and then the drug concentrations resulting in 50% growth inhibition in optical density for the strains are compared. When metabolic activation effect is observed, $9 mixture is added to the test tube during the treatment.