Formation of spectral intermediate G-C and A-T anion complex in duplex DNA studied by pulse radiolysis.
The dynamics of electron adducts of 2'-deoxynucleotides and oligonucelotides (ODNs) were measured spectroscopically by nanosecond pulse radiolysis. The radical anions of the nucleotides were produced within 10 ns by the reaction of hydrated electrons (e(aq)(-)) and were protonated to form the corresponding neutral radicals. At pH 7.0, the radical anion of deoxythymidine (dT(*-)) was protonated to form the neutral radical dT(H)(*) in the time range of microseconds. The rate constant for the protonation was determined as 1.8 x 10(10) M(-1) s(-1). In contrast, the neutral radical of dC(H)(*) was formed immediately after the pulse, suggesting that the protonation occurs within 10 ns. The transient spectra of excess electrons of the double-stranded ODNs 5'-TAATTTAATAT-3' (AT) and 5'-CGGCCCGGCGC-3' (GC) differed from those of pyrimidine radicals (C and T) and their composite. In contrast, the spectra of the electron adducts of the single-stranded ODNs GC and AT exhibited characteristics of C and T, respectively. These results suggest that, in duplex ODNs, the spectral intermediates of G-C and A-T anions complex were formed. On the microsecond time scale, the subsequent changes in absorbance of the ODN AT had a first-order rate constant of 4 x 10(4) s(-1), reflecting the protonation of T.
The Institute of Scientific and Industrial Research, Osaka University, Mihogaoka 8-1, Ibaraki Osaka 567-0047, Japan.
Ryuhei
R
Yamagami
Kazuo
K
Kobayashi
Seiichi
S
Tagawa
D020029:Base Pairing; D004247:DNA / Q000737:chemistry*; D003838:Deoxyadenine Nucleotides / Q000737:chemistry; D003845:Deoxycytosine Nucleotides / Q000737:chemistry; D003848:Deoxyguanine Nucleotides / Q000737:chemistry; D006863:Hydrogen-Ion Concentration; D009841:Oligonucleotides / Q000737:chemistry; D011675:Pulse Radiolysis / Q000379:methods; D013936:Thymidine / Q000737:chemistry
D003838:Deoxyadenine Nucleotides; D003845:Deoxycytosine Nucleotides; D003848:Deoxyguanine Nucleotides; D009841:Oligonucleotides; D004247:DNA; D013936:Thymidine