MUTAGENICITY OF TRYPTOPHAN PHOTOPRODUCTS IN THE AMES SALMONELLA ASSAY

During the photolysis of tryptophan a large number of products is form ed. In this study, aqueous solutions of tryptophan were irradiated by ultraviolet light during 5, 20 or 40 h. Each of the irradiated batches was divided into two aliquots, which were freeze-dried or extracted w ith chloroform. For each batch the latter extract was subsequently div ided into a purified chloroform extract and a methanol extract. Aliquo ts of the purified chloroform extracts were fractionated and pooled, p eakwise, into seven fractions. A recombined sample was also constructe d. All extracts and samples were tested for mutagenicity using the sta ndard Ames Salmonella assay. The results indicate an exposure time dep endent increase in mutagenicity of the extracts, as seen with tester s train TA100 both with and without metabolic activation. The mutagenici ty of the freeze-dried extracts well approximated the mutagenicity of the chloroform extracts, indicating that most mutagenicity can be extr acted with chloroform. With the fractions the highest mutagenic respon ses were seen in the late, i.e., less lipophilic fractions. This respo nse pattern seen in TA98 and TA100, mainly with S9 activation, was in contrast to the response of TA102 without S9, which was highest to the more lipophilic fractions. On a fraction level, no general exposure d ependent increase of mutagenicity was observed. The results also show that photooxidation of tryptophan gives rise to a different spectrum o f products compared to pyrolysis. Both processes result in compounds w ith strong biological effects. Photooxidation results in compounds wit h low genotoxicity and high Ah receptor affinity while pyrolysis gener ates compounds with high genotoxicity and low or no Ah receptor affini ty.