Generation of radical species by irradiation of tryptophan and tyrosine solutions sensitized by riboflavin: biological implications

RESUMO

The photoconversion of tryptophan and tyrosine sensitized by riboflavin, was studied in aerobic and anaerobic atmospheres. Tyrosine photodegradation occurs by a radical mechanism (Type I). In contrast, the tryptophan photoconversion shows characteristics of both Type I and Type II ((1)O2 mediated) mechanisms. The main tyrosine photoproduct was dityrosine while for tryptophan a complex mixture of indolic, flavinic and indolic-flavinic type aggregates was obtained. The products of the thermolysis of 2,2'-azobis(2-amidinopropane) hydrochloride in the presence of each amino acid were of the same type as those of the photochemical reactions. The photoproducts of both amino acids are toxic when added to mouse tumoral cells in culture. A more deleterious effect was observed when anaerobic conditions were used, and also when tryptophan photoproducts were added.