Direct observation of guanine radical cation deprotonation in duplex DNA using pulse radiolysis.
The dynamics of one-electron oxidation of guanine (G) base mononucleotide and that in DNA have been investigated by pulse radiolysis. The radical cation (G+*) of deoxyguanosine (dG), produced by oxidation with SO(4)-*, rapidly deprotonates to form the neutral G radical (G(-H)*) with a rate constant of 1.8 x 10(7) s(-1) at pH 7.0, as judged from transient spectroscopy. With experiments using different double-stranded oligonucleotides containing G, GG, and GGG sequences, the absorbance increases at 625 nm, characteristic of formation of the G(-H)*, were found to consist of two phases. The rate constants of the faster ( approximately 1.3 x 10(7) s(-1)) and slower phases ( approximately 3.0 x 10(6) s(-1)) were similar for the different oligonucleotides. On the other hand, in the oligonucleotide containing G located at the 5'- and 3'-terminal positions, only the faster phase was seen. These results suggest that the lifetime of the radical cation of the G:C base pair (GC+*), depending on its location in the DNA chain, is longer than that of free dG. In addition, the absorption spectral intermediates showed that hole transport to a specific G site within a 12-13mer double-stranded oligonucleotide is complete within 50 ns; that is, the rate of hole transport over 20 A is >10(7) s(-1).
Kobayashi
Kazuo
K
The Institute of Scientific and Industrial Research, Osaka University, Mihogaoka 8-1, Ibaraki Osaka 567-0047, Japan. kobayashi@sanken-osaka.u.ac.jp
Tagawa
Seiichi
S
D002412:Cations / Q000737:chemistry; D004247:DNA / Q000737:chemistry*; D005609:Free Radicals / Q000737:chemistry; D006147:Guanine / Q000737:chemistry*; D009841:Oligonucleotides / Q000737:chemistry; D010084:Oxidation-Reduction; D011522:Protons; D011675:Pulse Radiolysis
D002412:Cations; D005609:Free Radicals; D009841:Oligonucleotides; D011522:Protons; D006147:Guanine; D004247:DNA