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Variation of the frameshift activity of a mutagen (ICR-191) following nitrosation in human gastric juice.

The acridine half-mustard mutagen ICR-191 elicits peculiar frameshift mutations in S. typhimurium, which are greatly decreased in the presence of rat liver preparations. Following in vitro preincubation of ICR-191 with sodium nitrite and human gastric juice, these patterns of mutation are replaced by frameshift errors requiring metabolic activation and showing a different molecular specificity.