Tyrosine dimer, a common oxidative lesion of proteins, is able to act as an intrinsic photosensitizer

M. LAURA DÁNTOLA; LARA O. REID; ANDRÉS H. THOMAS; MARIANA VIGNONI

Barcelona

Congreso; 17th Congress of the International Union of Photobiology and 18th Congress of the European Society for Photobiology; 2019

ESP - IUPB

IntroductionThe tyrosine dimer (Tyr2), acovalent bond between two tyrosines (Tyr), is one of the most importantmodifications of the oxidative damage of proteins. This compound isincreasingly used as a marker of aging, stress and pathogenesis. Atphysiological pH, Tyr2 is able to absorb radiation at wavelengthssignificantly present in the solar radiation and artificial sources of light.As a result, when Tyr2 is formed invivo, a new chromophore appears in the proteins. Despite the biomedicalimportance of Tyr2, the information of its photochemical propertiesis limited due to the drawbacks of its synthesis. Results and DiscussionWe have optimized a simple, one-step method tosynthesize Tyr2, using pterin (Ptr) as a photocatalyst. Ourprocedure is carried out in aqueous solutions under UV-A radiation for fewminutes. The purification of Tyr2 is performed by reverse-phasechromatography. The highly pure solution obtained was used to deeper study itsphotochemical properties.We have studied the photodegradation of theacid and alkaline form of Tyr2 in aqueous solution under UV-B andUV-A radiation. In the absence of oxygen Tyr2 is photostable. On theother hand, excitation in the presence of oxygen leads to the photodegradationof Tyr2, yielding different products, which conserve the dimericstructure. During its photodegradation different reactive oxygen species, likehydrogen peroxide, superoxide anion and singlet oxygen (1O2),are produced. The quantum yield of 1O2 production is 0.15± 0.05, which is similar to that obtained for free Tyr. In addition, Tyr2is able to sensitize the photodegradation of Tyr.Conclusions This study indicates that when Tyr2 is generated in a proteinstructure, an intrinsic potential photosensitizer is formed, extending theactive fraction of light towards the UV-A range. Therefore a product of aphotosensitized process can act as a photosensitizer itself leading to furtherphotosensitized damage, thus amplifying the harmful effects of UV radiation onbiological systems.AcknowledgementsCONICET-Grant PIP 2013-0304, ANPCyT-Grant PICT-2012?0508,PICT-2015?1988, UNLP-Grant X712.Conflicts ofInterestThere are no conflicts to declare.ReferencesD. Balasubramanian, R. Kanwar, Mol. Cel. Biochem., 2002,234/235, 27-38.L. O. Reid et al.,Dyes Pigm. 2017, 147, 67-74.L. O. Reid et al., Photochem. Photobiol. Sci., in press (DOI: 10.1039/C9PP00182D)