Photodegradation of tryptophan in wool

The amino acid tryptophan is degraded upon light exposure or during acid and oxidative treatments. After irradiation of tryptophan solutions, the photodegradation products N′-formylkynurenine, kynurenine, tryptamine, and oxindolylalanine were identified by means of HPLC. These photoproducts of tryptophan contribute to the photoyellowing of wool. Oxygen plays a major role in tryptophan photodegradation. An attack of oxygen at the indole residue initiates the photodegradation reaction. The main photodegradation of tryptophan in proteins (e. g. in polytryptophan or in wool) is the cleavage of the indole ring and the formation of kynurenines. In irradiated wool, only N′-formylkynurenine was detected. N′-Formylkynurenine is known to be a photosensitiser.