Photosensitization of 2’-deoxyadenosine 5’-monophosphate by lumazine: mechanism and products analysis

M. PAULA DENOFRIO; ANDRÉS H. THOMAS; ESTHER OLIVEROS; CAROLINA LORENTE

Ferrara, Italia

Simposio; XXIII IUPAC Symposium on Photochemistry; 2010

UV radiation induces damages to the DNA molecule and its components throughphotosensitized reactions[1,2]. Among these processes, photosensitized oxidations may occurthrough electron transfer or hydrogen abstraction (type I mechanism) and/or the production ofsinglet molecular oxygen (1O2) (type II mechanism). Lumazines belongs to an important family(Pteridines) of heterocyclic compounds present in biological systems as biosynthetic precursorsand/or products of metabolic degradation. Some pteridines are able to photoinduce chemicalchanges to double-stranded DNA[3,4]. In recent studies it was demonstrated that both type I andtype II mechanisms can take place simultaneously under UV-A irradiation [5,6,7].To evaluate the capability of lumazines to act as photosensitizers through type I mechanism,we have investigated the oxidation of 2’-deoxyadenosine 5’-monophosphate (dAMP)photosensitized by lumazine (pteridine-2,4(1,3H)-dione; Lum) in aqueous solutions under UVirradiation. The photochemical reactions were followed by UV/VIS spectrophotometry, HPLC,electrochemical measurement of dissolved O2 and an enzymatic method for H2O2 determination.Photoproducts were analyzed by means of electrospray ionization mass spectrometry.Mechanistic analysis indicates that the acid form of Lum (pH=5.5) photoinduces thedegradation of dAMP by an electron transfer process. In this mechanism, the excitation of Lum isfollowed by an electron transfer from the dAMP molecule to the Lum triplet excited state, leadingto the formation of the corresponding ion radicals (Lum•– and dAMP•+). In the following step, theelectron transfer from Lum•– to O2 regenerates Lum and forms the superoxide anion. The latter maydisproportionate with its conjugated acid (HO2•) to form H2O2 or react with dAMP•+ to regeneratedAMP. Some photoproducts were found and analysed. In particular, 8-oxo-dAMP is formed duringthe photosensitization of dAMP by Lum, a typical product of type I photosensitized reactions. Incontrast, no evidence of a photochemical reaction induced by the basic form of Lum (pH 10.5) wasobserved.[1] Ravanat, J. -L.; Douki, T.; Cadet, J.; J. Photochem. Photobiol. B: Biol. 2001, 63, 88-102.[2] Cadet, J.; Sage, E.; Douki, T.; Mutat. Res. 2005, 571, 3-17.[3] Ito, K.; Kawanishi, S.; Biochemistry 1997, 36, 1774–1781.[4] Lorente, C.; Thomas, A. H.; Villata, L.; Hozbor, D.; Lagares, A.; Capparelli, A. L.; Pteridines2000, 11, 100-105.[5] Petroselli, G.; Dántola, M. L.; Cabrerizo, F. M.; Capparelli, A. L.; Lorente, C.; Oliveros, E.;Thomas, A. H.; J. Am. Chem. Soc. 2008, 130, 3001–3011.[6] Petroselli, G.; Erra-Balsells, R.; Cabrerizo, F. M.; Lorente, C.; Capparelli, A. L.; Braun, A. M.;Oliveros, E.; Thomas, A. H.; Org. Biomol.Chem. 2007, 5, 2792–2799.[7] Denofrio, M. P.; Hatz, S.; Lorente, C.; Cabrerizo, F. M.; Ogilby, P. R.; Thomas, A. H.;Photochem. Photobiol. Sci. 2009, 8, 1539-1549.