Formation of highly fluorescent adducts between 2′-deoxyguanosine and amino acids by ionizing radiation

Gamma-irradiation of aqueous solutions containing DNA and alcohols is known to generate fluorescent products. In this study, aqueous solutions containing 2′-deoxyguanosine (dG) and amino acids with an aliphatic hydroxyl group [serine (Ser) or threonine (Thr)] were irradiated and analyzed for fluorescence. Both irradiated solutions showed a similar fluorescence profile with the excitation maximum ∼310 nm and the emission maximum ∼370 nm. The fluorescence profiles were very close to that of 2-aminopurine, known as a highly fluorescent base. In the irradiation of dG with Ser, two distinct fluorescent products were observed in liquid chromatographic analysis. The major product was further purified by chromatography. Mass spectrometry (MS) showed that the major fluorescent product was a dG adduct bearing a Ser fragment at the C-6 position. In the case of dG with Thr, only one major fluorescent product was observed. The purified product seemed to be a C-6 adduct of dG with a Thr fragment based on MS and NMR analyses. These structural data for the fluorescent products suggest that C-6 adduct formation of dG was the key to generating fluorescence. This is consistent with our previous finding that the adduct between dG and tert-butanol at C-6 is highly fluorescent.