Host: The Japan Radiation Research Society
Deprotonation of the guanine radical cation in DNA is an important step in hole hopping and mutagenesis. The dynamics of one-electron oxidation of DNA have been investigated by pulse radiolysis. We proposed that the kinetics associated with the deprotonation process involves a shift of the N1 proton in G cation radical to its partner C, followed by final release of the proton into solution. In experiments using 5-substituted cytosine-modified oligonucleotides, changes of the cytosine C5 hydrogen to methyl or bromine groups resulted in an increase or decrease, respectively. Kinetic solvent isotope effects on the oxidation kinetics of dG and oligonucleotide duplexes were examined in H2O and D2O. The rate constant of formation of G radical in dG was larger by a factor of 1.7 than was the same rate constant in H2O . In the oligonucleotide, on the other hand, a remarkable solvent isotope effect of 3.8 was observed. These results suggest that the slower kinetic phase is due to the deprotonation of oxidized hydrogen-bridged G-C base pair by a water molecule.
