Mechanism of electron transfer processes photoinduced by lumazine.
UV-A (320-400 nm) and UV-B (280-320 nm) radiation causes damage to DNA and other biomolecules through reactions induced by different endogenous or exogenous photosensitizers. Lumazines are heterocyclic compounds present in biological systems as biosynthetic precursors and/or products of metabolic degradation. The parent and unsubstituted compound called lumazine (pteridine-2,4(1,3H)-dione; Lum) is able to act as photosensitizer through electron transfer-initiated oxidations. To get further insight into the mechanisms involved, we have studied in detail the oxidation of 2'-deoxyadenosine 5'-monophosphate (dAMP) photosensitized by Lum in aqueous solution. After UV-A or UV-B excitation of Lum and formation of its triplet excited state ((3)Lum*), three reaction pathways compete for the deactivation of the latter: intersystem crossing to singlet ground state, energy transfer to O(2), and electron transfer between dAMP and (3)Lum* yielding the corresponding pair of radical ions (Lum˙(-) and dAMP˙(+)). In the following step, the electron transfer from Lum˙(-) to O(2) regenerates Lum and forms the superoxide anion (O(2)˙(-)), which undergoes disproportionation into H(2)O(2) and O(2). Finally dAMP˙(+) participates in subsequent reactions to yield products.
Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicadas (INIFTA), Departamento de Química, Facultad de Ciencias Exactas, Universidad Nacional de La Plata, CCT La Plata-CONICET. Casilla de Correo 16, Sucursal 4, (1900), La Plata, Argentina.
M Paula
MP
Denofrio
M Laura
ML
Dántola
Patricia
P
Vicendo
Esther
E
Oliveros
Andrés H
AH
Thomas
Carolina
C
Lorente
D003838:Deoxyadenine Nucleotides / Q000737:chemistry; D004579:Electron Transport; D006863:Hydrogen-Ion Concentration; D010084:Oxidation-Reduction; D055668:Photochemical Processes; D017319:Photosensitizing Agents / Q000737:chemistry*; D011621:Pteridines / Q000737:chemistry*; D012995:Solubility; D013481:Superoxides / Q000737:chemistry
D003838:Deoxyadenine Nucleotides; D017319:Photosensitizing Agents; D011621:Pteridines; D013481:Superoxides; C008297:lumazine; C012873:2'-deoxy-5'-adenosine monophosphate