title: Histidine oxidation photosensitized by pterin: pH dependent mechanism.
abstract: Aromatic pterins accumulate in the skin of patients suffering from vitiligo, a chronic depigmentation disorder, due to the oxidation of tetrahydrobiopterin, the biologically active form of pterins. In this work, we have investigated the ability of pterin, the parent compound of aromatic pterins, to photosensitize the oxidation of histidine in aqueous solutions under UV-A irradiation. Histidine is an α-amino acid with an imidazole functional group, and is frequently present at the active sites of enzymes. The results highlight the role of the pH in controlling the competition between energy and electron transfer mechanisms. It has been previously demonstrated that pterins participate as sensitizers in photosensitized oxidations, both by type I (electron-transfer) and type II mechanisms (singlet oxygen ((1)O2)). By combining different analytical techniques, we could establish that a type I photooxidation was the prevailing mechanism at acidic pH, although a type II mechanism is also present, but it is more important in alkaline solutions.
authors.affiliation: Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicadas (INIFTA), Departamento de Química, Facultad de Ciencias Exactas, Universidad Nacional de La Plata, CCT La Plata-CONICET, Boulevard 113 y 64, 1900 La Plata, Argentina.
authors.forename: Carolina
authors.initials: C
authors.lastname: Castaño
authors.affiliation: Laboratoire des Interactions Moléculaires et Réactivité Chimique et Photochimique (IMRCP), UMR 5623-CNRS/UPS, Université Toulouse III (Paul Sabatier), 118, route de Narbonne, F-31062 Toulouse cédex 9, France.
authors.forename: Esther
authors.initials: E
authors.lastname: Oliveros
authors.affiliation: Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicadas (INIFTA), Departamento de Química, Facultad de Ciencias Exactas, Universidad Nacional de La Plata, CCT La Plata-CONICET, Boulevard 113 y 64, 1900 La Plata, Argentina.
authors.forename: Andrés H
authors.initials: AH
authors.lastname: Thomas
authors.affiliation: Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicadas (INIFTA), Departamento de Química, Facultad de Ciencias Exactas, Universidad Nacional de La Plata, CCT La Plata-CONICET, Boulevard 113 y 64, 1900 La Plata, Argentina. Electronic address: clorente@inifta.unlp.edu.ar.
authors.forename: Carolina
authors.initials: C
authors.lastname: Lorente
mesh_terms: D002851:Chromatography, High Pressure Liquid; D004579:Electron Transport; D006639:Histidine / Q000737:chemistry*; D006863:Hydrogen-Ion Concentration; D010084:Oxidation-Reduction; D017319:Photosensitizing Agents / Q000737:chemistry*; D011622:Pterins / Q000737:chemistry*; D026082:Singlet Oxygen / Q000737:chemistry / Q000378:metabolism; D013056:Spectrophotometry, Ultraviolet; D013816:Thermodynamics; D014466:Ultraviolet Rays
chemical_list: D017319:Photosensitizing Agents; D011622:Pterins; D026082:Singlet Oxygen; D006639:Histidine
keywords: Histidine; Photosensitization; Pterin