Degradation of α-melanocyte-stimulating hormonephotosensitized by pterin

CAROLINA CASTAÑO; CAROLINA LORENTE; NATHALIE MARTINS-FROMENT ; ESTHER OLIVEROS; ANDRÉS H. THOMAS

Cordoba

Congreso; 16th International Congress of Photobiology; 2014

Universidad Nacional de Cordoba

Oxidized pterins, efficient photosensitizers under UV-A irradiation, accumulate in the skin of patients suffering from vitiligo, a chronic depigmentation disorder. In this work, we have investigated the ability of pterin (Ptr), the parent compound of oxidized pterins,to photosensitize the oxidation of the peptide α-melanocyte-stimulating hormone (α-MSH), which stimulates the production and release of melanin by melanocytes in skin and hair. Our results show that Ptr is able to photoinduce the degradation of α-MSH upon UV-A irradiation and that the reaction is initiated by an electron transfer from the peptide to the triplet excited stated of Ptr. The photosensitized process leads to the oxidation of the peptide and to the degradation of, at least, tryptophan (Trp) and tyrosine (Tyr) residues. It can thus be inferred that the incorporation of oxygen atoms takes place at least in these α-MSH residues. In addition, the dimerization of the peptide was also observed and dimers of theTyr radical were detected in the treated peptide, indicating that Ptr may photoinduce crosslinking of peptides.The evolution of the reactions was followed by UV-Vis spectrometry and products were analyzed by HPLC, UPLC-MS and fluorescence.