Inhibitory effects of para-aminobenzoic acid on the formation and mutagenicity of N-nitroso compounds.

Naturally occurring para-aminobenzoic acid (PABA) inhibited the formation of N-methyl-N-nitrosourea (MNU) from a nitrosation mixture of N-methylurea and nitrite at pH 3. The suppressive effect of PABA on the formation of MNU is higher than that of ascorbic acid. The presence of the MNU was assayed by its mutagenicity in a higher plant, Arabidopsis thaliana. In addition, PABA markedly reduced the mutagenicity of N-methyl-N'-nitro-N-nitrosoguanidine in A.thaliana, but had no or only a low inhibitory effect on the mutagenicity of preformed MNU and on the promutagen N-nitrosodimethylamine.