Modification of DNA bases by photosensitized one-electron oxidation

Purpose: To determine the distribution of base damage within isolated DNA u pon oxidation by three type I photosensitizers in aerated aqueous solution. Materials and methods: Aqueous solutions of DNA were exposed to UVA in the presence of riboflavin, benzophenone or menadione. Then, eight modified nuc leobases were measured, using HPLC-EC, GC-MS or HPLC with fluorescence dete ction. Results: The three photosensitizers led to a predominant degradation of guanine bases within DNA. The relative yield of the three main guanine degradation products measured in DNA was similar with the three sensitizers . 8-OxodAdo was also produced in an almost constant yield with respect to i ts guanine analogue. The yield of oxidized pyrimidines was lower and was fo und to depend on the photosensitizer used. The results were compared with t he yield of photosensitization-induced degradation of the 2'-deoxyribonucle osides. Conclusion: The favoured photosensitized degradation of guanine within DNA may be explained by its lower oxidation potential with respect to that of t he other bases, together with the occurrence of charge transfer through DNA . The base modification pattern determined in the present work is different from that obtained upon reaction of hydroxyl radicals. Under the latter co nditions, pyrimidine oxidation products were generated more efficiently tha n by photosensitized one-electron oxidation.