Mechanism and products of the photosensitization of amino acids and nucleotides by pterins

SERRANO, MARIANA PAULA; REID, LARA O.; ESTEBANEZ RUIZ, SANDRA; CASTAÑO,CAROLINA; OLIVEROS, ESTHER; THOMAS, ANDRÉS H.; LORENTE, CAROLINA; DANTOLA, MARIA LAURA

Tampa, Florida

Congreso; 2018 Biennial Meeting, American Society for Photobiology; 2018

American Society for Photobiology

The biological andmedical importance of photosensitized reactions is mostly related to theirparticipation in processes involved in the development of skin cancer. Pterinsare a family of heterocyclic compounds widespread in living systems. Thesebiomolecules are photochemically active and, under UV-A excitation (320?400nm), can fluoresce, produce organic radicals and reactive oxygen species, suchas singlet oxygen, and undergo photooxidation reactions to generate variousproducts. Our group has investigated for more than 10 years, the degradation ofamino acids and nucleotides photosensitized by pterins under UV-A irradiation. Ourstudies included the interaction of singlet and triplet excited states ofpterins with different substrates, radical species detection and identificationof products under different experimental conditions. On the basis of thesedata, we present in this work a summary of the mechanisms involved in thepterin-photosensitized degradation of amino acids and nucleotides in aqueoussolutions. We also discuss the products formed and the corresponding damage toDNA and proteins. Most of the processes are initiated by an electron transfer fromthe substrate to the triplet excited state of the photosensitizer (type Imechanism).The processes undergone by the radical cation (or the correspondingneutral radical formed after deprotonation) include hydration, reaction withoxygen, reaction with the superoxide anion, dimerizationand reaction with the radical anion of the sensitizer. The singlet oxygenmediated oxidation may also occur (type II mechanism). The relative contributionof the different pathways depends on the experimental conditions and on the natureof the substrate.