Degradation of alfa-melanocyte-stimulating hormone photosensitized by pterin

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

Córdoba

Congreso; 16th International Congress on Photobiology; 2014

International Union of Photobiology

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 alfa-melanocyte-stimulating hormone (a-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 a-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 be inferred that the incorporation of oxygen atoms takes place in Trp and Tyr residues of a-MSH. In addition, the dimerization of the peptide was also observed and dimers of Tyr radical were detected in the treated peptide, which indicates 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..  Acknowledgments Consejo Nacional de Investigaciones Cientificas y Técnicas (CONICET-Grant PIP 0425) and Universidad Nacional de La Plata (UNLP-Grant X586)  [1] D. I. Pattison, et. al. ,  Photochem. Photobiol. Sci., 2012, 11, 38?53 [2] A. H. Thomas, et. al., Free Radic. Biol. Med., 2013, 63, 467?475. [3] C. Castaño, et. al., Photochem. Photobiol., 2013, 89, 1448?1455. [4] K. V. Neverov, et. al.  Biochemistry (Moscow), 1996, 61, 1149?1155.