Oxidation of 2'-Deoxyguanosine 5'-Monophosphate Photoinduced by Pterin: Type I versus Type II Mechanism

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• 作者：Gabriela Petroselli ; M. Laura Dá ; ntola ; Franco M. Cabrerizo ; Alberto L. Capparelli ; Carolina Lorente ; Esther Oliveros ; Andr&eacute ; s H. Thomas
• 刊名：Journal of the American Chemical Society
• 出版年：2008
• 出版时间：March 12, 2008
• 年：2008
• 卷：130
• 期：10
• 页码：3001 - 3011
• 全文大小：184K
• 年卷期：v.130,no.10(March 12, 2008)
• ISSN：1520-5126

文摘

UV-A radiation (320-400 nm) induces damage to the DNA molecule and its components throughdifferent photosensitized reactions. Among these processes, photosensitized oxidations may occur throughelectron transfer or hydrogen abstraction (type I) and/or the production of singlet molecular oxygen (¹O₂)(type II). Pterins, heterocyclic compounds widespread in biological systems, participate in relevant biologicalprocesses and are able to act as photosensitizers. We have investigated the photosensitized oxidation of2'-deoxyguanosine 5'-monophosphate (dGMP) by pterin (PT) in aqueous solution under UV-A irrradiation.Kinetic analysis was employed to evaluate the participation of both types of mechanism under different pHconditions. The rate constant of ¹O₂ total quenching (k_t) by dGMP was determined by steady-state analysisof the ¹O₂ NIR luminescence, whereas the rate constant of the chemical reaction between ¹O₂ and dGMP(k_r) was evaluated from kinetic analysis of concentration profiles obtained by HPLC. The results show thatthe oxidation of dGMP photosensitized by PT occurs through two competing mechanisms that contributein different proportions depending on the pH. The dominant mechanism in alkaline media involves thereaction of dGMP with ¹O₂ produced by energy transfer from the PT triplet state to molecular oxygen (typeII). In contrast, under acidic pH conditions, where PT and the guanine moiety of dGMP are not ionized, themain pathway for dGMP oxidation involves an initial electron transfer between dGMP and the PT tripletstate (type I mechanism). The biological implications of the results obtained are also discussed.