The influence of pH on the mutagenicity in yeast of N-methylnitrosamides and nitrous acid

Summary In a reverse mutation system with the haploid, adenine requiring strain, ad_6–45, of Saccharomyces cerevisiae it could be demonstrated that N-methyl-nitrosamides are highly mutagenic down to ph 2. By chemical methods it could be shown that nitrosamides decompose into nitrous acid at ph 2.2–2.3. Moreover, in the case of NMG, NMH and NMU, deamination of adenine to hypoxanthine was found to occur at pH 2. These results led to the conclusion that N-methyl-nitrosamides at low pH possibly exert their mutagenicities via deamination by nitrous acid besides the alkylation by diazomethane probably prevailing at higher pH. Mere incubation of yeast cells in buffers of low pH was not mutagenic.