Photosensitizing properties of biopterin and its photoproducts using 20-deoxyguanosine 50-monophosphate as an oxidizable target

MARIANA P. SERRANO; CAROLINA LORENTE; FAUSTINO E. MORAN VIEYRA; CLAUDIO D. BORSARELLI; ANDRÉS H. THOMAS

PHYSICAL CHEMISTRY CHEMICAL PHYSICS

ROYAL SOC CHEMISTRY

Lugar: CAMBRIDGE; Año: 2012

1463-9076

UV-A radiation (320–400 nm) induces damages to the DNA molecule and its components through photosensitized reactions. Biopterin (Bip) and its photoproducts 6-formylpterin (Fop) and 6-carboxypterin (Cap) accumulate in the skin of human beings suffering from vitiligo, a depigmentation disorder where the protection against UV radiation fails because of the lack of melanin. The photosensitizing properties of Bip, Fop and Cap in aqueous solution were investigated using the nucleotide 2’-deoxyguanosine 5’-monophosphate (dGMP) as oxidizable target. Steady-state and time-resolved experiments were performed to elucidate the mechanisms involved in the photosensitized oxidation of dGMP by pterins. The three pterin derivatives are able to photosensitize dGMP, being Fop the most efficient sensitizer. The reactions proceed through two competing pathways: (1) electron transfer from dGMP to triplet excited-state of pterins (Type I mechanism) and (2) reaction of dGMP with 1O2 produced by pterins (Type II mechanism). Kinetic analysis revealed that the electron transfer pathway is the main mechanism and the interaction of dGMP with the triplet excited-state of pterins and the formation of the corresponding dGMP radicals were demonstrated by laser flash photolysis experiments. The biological implications of the results obtained are also discussed.