Photosensitization of albumin by pterin

ANDRÉS H. THOMAS; CAROLINA LORENTE; CONSTANZA GONZÁLEZ; M. LAURA DÁNTOLA

Congreso; XI Encuentro Latinoamericano de Fotoquímica y Fotobiología; 2012

UV-A radiation (320-400 nm) causes chemical changes in biomacromolecules through photosensitized reactions. This indirect action may take place through different mechanisms: energy transfer from the triplet state of the photosensitizer to the substrate and photosensitized oxidations, which can involve the generation of radicals (type I mechanism), e.g., via electron transfer or hydrogen abstraction, and/ or the production of singlet oxygen (1O2) (type II mechanism) [[i]]. 5,6,7,8-Tetrahydrobiopterin (H4Bip) is an essential cofactor in the hydroxylation of the aromatic amino acids. The importance of this cofactor in the human epidermis and its participation in the regulation of melanin biosynthesis are well recognized [[ii]]. Vitiligo is a skin disorder characterized by the acquired loss of constitutional pigmentation manifesting as white macules and patches [[iii]]. In this disease the H4Bip metabolism is altered and oxidized pterins accumulate in the affected tissue, where the protection against UV radiation fails due to the lack of melanin, the main pigment of skin. Therefore, the photochemistry of pterins is of particular interest for the study of this disease. The photochemistry of oxidized pterins has been studied and, in particular, it has been demonstrated that they are able to photoinduced DNA damage [[iv]] and can act as photosensitizer through both type I and type II mechanisms [[v]]. However, to the best of our knowledge, no study has been reported on processes photosensitized by pterins that affect proteins. Therefore, given the important biological and medical ramifications of the photosensitizing properties of pterins, we set out to investigate the damage of bovine serum albumin (BSA) photoinduced by pterin (Ptr), the parent and unsubstituted compound of oxidized pterins. Aqueous solutions of BSA where expose to UV-A radiation in the presence of Ptr. The irradiated solutions where analyzed by UV/vis spectrophotometry, HPLC, an enzymatic method for H2O2 determination and electrophoresis in polyacrylamide gels. Results showed that Ptr is able to photoinduce damage to BSA. In particular, electrophoretic analysis revealed the formation of compounds of molecular weights higher than that of BSA, suggesting that a cross-linking process takes place. [[i]].      Cadet, J.; Sage, E.; Douki, T. Mutat. Res. 571, 3, 2005. [[ii]].      Schallreuter, K. U.; Wood, J. M.; Pittelkow, M. R; Gütlich, M.; Lemke, K. R.; Rödl, W.; Swanson, N. N.; Hitzemann, K.; Ziegler, I. Science 263, 1444, 1994. [[iii]].     Glassman, S. J. Clin. Sci. 120, 99, 2011. [[iv]].    Ito, K.; Kawanishi, S. Biochemistry 36, 1774, 1997. [[v]].     Petroselli, G.; Dántola, M. L.; Cabrerizo, F. M.; Capparelli, A. L.; Lorente, C.; Oliveros, E.; Thomas, A. H. J. Am. Chem. Soc. 130, 3001, 2008.