Mutagenic activities of tryptophan metabolites before and after nitrite treatment

The mutagenic activities of 16 kinds of tryptophan metabolites, before and after nitrite treatment, were examined in the Ames test. None of the compounds showed mutagenic activity before nitrite treatment. After nitrite treatment under acidic conditions, 11 compounds showed mutagenic activity towards Salmonella typhimurium TA100 strain in the absence of a metabolic activation system. Tryptophan induced 1000 revertant colonies/mumol, while 5-hydroxyindole, 5-hydroxytryptamine and 3-hydroxykynurenine, all containing a hydroxy group in the molecule, induced 11,000, 5200 and 2700 revertant colonies/mumol, respectively. These results indicate that the introduction by nitrite treatment of a hydroxy group into the indole or benzene ring of tryptophan-related compounds increases their mutagenic activity.