The effects of various weak-, non-, and co-carcinogenic chemicals on 2-acetylaminofluorene-induced mutation in Salmonella typhimurium were studied. We found that a single co-mutagen could provide for either enhanced or decreased mutagenesis. A differential effect on mutagenic expression was dependent upon: (1) the type of inducer of S-9 (supernatant from liver homogenate centrifuged at 9000 × g) liver enzymes; (2) the amount of S-9 enzyme preparation employed; and (3) the combined dose of mutagen plus co-mutagen studied. No effect was observed in the absence of S-9. Our data suggest that in S. typhimurium a primary factor in the alteration of mutagenesis by a combination of chemicals is changes in metabolism of the principal mutagen.
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