Lack of comutagenicity by norharman and other compounds on revertants induced by photolabeling with 2-azido-9-fluorenone oxime

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Mutations were induced by photolabeling 2-azido-9-fluorenone oxime in Salmonella typhimurium tester strain TA1538. Since the critical adducts were formed directly by the photogenerated nitrene, metabolic activation was bypassed. The bacteria themselves possessed the deep rough cell wall and uvrB − mutations, thereby minimizing comutagenic effects resulting from transport or DNA repair. This technique thus permitted detection of comutagenicity resulting from altneration in the binding of the mutagen to its critical receptor. No compound tested increased mutagenicity. Cholic acid had no effect at low dose, but inhibited mutagenicity at 10 −4 M, while trans-retinol had no effect at any concentration. Harman, norharman and ethidium reduced the number of mutants only slightly at concentrations from 10 −6 to 10 −5 M.