CONICET | Buscador de Institutos y Recursos Humanos

Pterins, heterocyclic compounds widespread in living systems, participate in relevant biological processes, such as metabolic redox reactions. Under UV-A excitation (320400 nm), pterins can fluoresce, undergo photooxidation to produce different products, generate reactive oxygen species (ROS) and photoinduce oxidation of biomolecules through electron transfer mechanisms. In this work, we investigated electron transfer pathways initiated by excited states of pterins generated by UV-A radiation. The generation of superoxide anion (O2‒) was investigated by electron paramagnetic resonance (EPR), using 5,5-dimethyl-1-pyrroline-N-oxide (DMPO) as spin-trap. To confirm the formation of O2‒ upon pterin (Ptr) photolysis, EPR experiments were performed in the presence of superoxide dismutase (SOD), enzyme that catalyzes the conversion of O2− into H2O2 and O2. In addition, photolysis of Ptr in the presence and in the absence of SOD was carried out. Irradiated solutions were analyzed by UV/VIS spectrophotometry, HPLC and an enzymatic method for H2O2 determination. The obtained EPR spectra correspond to the adduct DMPO-OOH, which suggest that DMPO has trapped superoxide anion. Moreover, the addition of SOD caused a drastic decrease of the EPR signal, confirming the formation of O2‒ in Ptr solutions upon UV-A irradiation. In another set of experiments, the rate of H2O2 formation in the presence of SOD was much higher than that measured in its absence. This result is in agreement with the data obtained in EPR experiments, but also implies the existence of recombination reactions that consume most O2‒ formed in the absence of SOD. Taking into account all the results, the following mechanism can be proposed