OXIDATION OF 2’-DEOXYADENOSINE 5’-MONOPHOSPHATE PHOTOINDUCED BY LUMAZINE.

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

Congreso; X Encuentro Latinoamericano de Fotoquímica y Fotobiología (ELAFOT); 2010

Keywords. Photosensitization; lumazine; electron transferUV radiation induces damages to the DNA molecule and its components through photosensitized reactions. Among these processes, photosensitized oxidations may occur through electron transfer or hydrogen abstraction (type I mechanism) and/or the production of singlet molecular oxygen (1O2) (type II mechanism). Lumazines are an important family of heterocyclic compounds present in biological systems as biosynthetic precursors and/or products of metabolic degradation. 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 UV irradiation.  The photochemical reactions were followed by UV/VIS spectrophotometry, HPLC, electrochemical measurement of dissolved O2 and an enzymatic method for H2O2 determination. Mechanistic analysis indicates that the acid form of Lum (pH=5.5) photoinduces the degradation of dAMP by an electron transfer process. In this mechanism, the excitation of Lum is followed by an electron transfer from dAMP molecule to the Lum triplet excited state, leading to the formation of the corresponding ion radicals (Lum•– and dAMP•+). In the following step, the electron transfer from Lum•– to O2 regenerates Lum and forms the superoxide anion. The latter may disproportionate with its conjugated acid (HO2•) to form H2O2 or react with dAMP•+ to regenerate dAMP.In contrast, no evidence of a photochemical reaction induced by the basic form of Lum (pH 10.5) was observed.References.Foote, C. S. Photochem. Photobiol. 1991, 54, 659Denofrio, M. P.; Thomas, A. H.; Braun, A. M.; Oliveros, E.; Lorente, C. J. Photochem. Photobiol. A: Chem. 2008, 200, 282