Pterins,
heterocyclic compounds widespread in
biological systems, accumulate in the skin of patients suffering from
vitiligo, a chronic depigmentation disorder.
Pterins have been previously identified as good
photosensitizers under UV-A irradiation. In this work, we have investigated the ability of
pterin (Ptr), the parent compound of oxidized
pterins, to photosensitize the oxidation of
tyrosine (Tyr) in aqueous solutions. Tyr is an important target in the study of the photodynamic effects of UV-A radiation because it is oxidized by
singlet oxygen ((1)O2) and plays a key role in polymerization and cross-linking of
proteins. Steady UV-A irradiation of solutions containing Ptr and Tyr led to the consumption of Tyr and dissolved O2, whereas the Ptr concentration remained unchanged. Concomitantly,
hydrogen peroxide (H2O2) was produced. By combining different analytical techniques, we could establish that the mechanism of the photosensitized process involves an electron transfer from Tyr to the triplet excited state of Ptr. Mass spectrometry, chromatography and fluorescence were used to analyze the photoproducts. In particular, oxygenated and dimeric compounds were identified.