Oxidation of purine nucleotides photoinduced by lumazine

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

Cubatao, San Pablo, Brasil.

Congreso; IX Encuentro Latinoamericano de Fotoquímica y Fotobiología (ELAFOT); 2008

Solar radiation is a genotoxic agent that induces modifications to genomic DNA and is implicated in the induction of human skin cancers. UV-B radiation (290-320 nm) is absorbed by the DNA, whereas UV-A radiation (320-400 nm), representing a larger proportion of the solar UV radiation, is not absorbed by DNA, and damage to DNA is thought to involve photosensitized processes (1). Along these lines of reasoning, it is important to evaluate the capacity of endogenous substances to photoinduce DNA damage and to search and characterize compounds that might be involved in photosensitized processes leading to the generation of mutations in vivo.             Lumazine belongs to a group of significant compounds called pteridines. They are presents in cells, and participate in relevant biological functions. Electronically excited states of lumazine can be generated by radiation in the UV-A and visible spectral domain and are able to produce reactive oxygen species, such as singlet oxygen (1O2) that can oxidize DNA and other biomolecules. (2) In this work, we present a study on the mechanisms involved in the oxidation of purine nucleotides photoinduced by lumazine. The experiments were performed in aqueous solution under UV-A radiation and 2´-deoxyguanosine 5´-monophosphate and 2´-deoxyadenosine 5´-monophosphate were used as target compounds. We have evaluated the effect of pH, investigated the participation of dissolved O2 and quantified the formation of H2O2. The participation of type I (electron transfer) and type II (1O2) mechanisms in acidic and alkaline media was analyzed by means of kinetic analysis. (1) R. M. Tyrrell, S. M. Keyse,   J. Photochem. Photobiol. B: Biol. 1990, 4, 349-361. (2) M. Paula Denofrio, A. H. Thomas, A. M. Braun, E. Oliveros, C. Lorente, J.Photochem. Photobiol.A: Chem. 2008, doi:10.1016/j.jphotochem.2008.08.003.