Photosensitized Oxidation of Free and Peptide Tryptophan to N -Formylkynurenine

The oxidation of proteins and, in particular, of tryptophan (Trp) residues leads to chemical modifications that can affect structure and function. The oxidative damage to proteins in photochemical processes is relevant in skin and eyes and is related to a series of pathologies triggered by the exposure to electromagnetic radiation.In this work we studied the photosensitized formation ofN-formylkynurenine (NFKyn) from Trp in different reaction systems. We used two substrates: free Trp and a peptide of nine amino acid residues, Trp being the only oxidizable residue.Two different photosensitizers were employed: Rose Bengal (RB) and pterin (Ptr). The former is a typical type II photosensitizer[acts producing singlet oxygen (1O2)]. Ptr is the parent compound of oxidized or aromatic pterins, natural photosensitizers that accumulate in human skin under certain pathological conditions and act mainly through type I mechanisms (generation of radicals).Experimental data were collected in steady photolysis and the irradiated solutions were analyzed by chromatography (HPLC). Results indicate that the reaction of Trp with 1O2 initiates the process leading to NFKyn, but different competitive pathways take place, depending on the photosensitizer and the substrate. In Ptr-photosensitization, type I mechanism is involved in secondary reactions accelerating the formation of NFKyn when free Trp is the substrate. Fil: Farías, Jesuán Javier. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicadas. Universidad Nacional de La Plata. Facultad de Ciencias Exactas. Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicadas; Argentina Fil: Dantola, Maria Laura. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicadas. Universidad Nacional de La Plata. Facultad de Ciencias Exactas. Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicadas; Argentina