Mutagenic effect by phenylalanine during gamma-irradiation of plasmid DNA in aqueous solution under oxic conditions

Irradiation of DNA in aqueous solution or in cells with gamma -rays results in different mutational spectra, indicating that in both situations differ ent patterns of DNA damages are induced. One of the causes for these differ ent types of damages might be the formation of secondary, organic radicals, if cells are irradiated. Some organic compounds, including the amino acid phenylalanine, are well known to produce radicals during irradiation. Under oxic conditions these secondary radicals react with oxygen, thus forming p eroxyl radicals which can be very harmful to DNA, and which may, therefore, induce DNA damage leading to mutations. This study examines the influence of the presence of phenylalanine during gamma -irradiation of DNA in aqueou s solution under oxic conditions. The results indicate that the formation o f phenylalanine radicals influences the types of induced mutations in the g amma -radiation-induced mutation spectrum. The most prominent difference is the increase in G:C to T:A transversions and the decrease in G:C to A:T tr ansitions in the presence of phenylalanine. Further, it appears that the ga mma -radiation-induced mutation spectrum after irradiation of DNA in aqueou s solution is more comparable to the intracellular gamma -radiation-induced mutation spectrum in E. coli cells, if phenylalanine is present during irr adiation. Therefore, these results suggest that the presence of phenylalani ne during irradiation of DNA in aqueous solution gives a better impression of gamma -radiation-induced mutations in bacterial systems than water only. (C) 2000 Elsevier Science B.V. All rights reserved.