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1983 (1)
1Author    Eberhard Bothe, G. Ali, Ureshi, D. Ietrich, S. Ch, Lte-F Ro, H. Lin DRequires cookie*
 Title    Rate of OH Radical Induced Strand Break Formation in Single Stranded DNA under Anoxic Conditions. An Investigation in Aqueous Solutions Using Conductivity Methods  
 Abstract    Single stranded D N A (ssD N A) in aqueous N 20-satu rated solution was pulse-irradiated with electrons or irradiated under steady-state conditions with 60Co-y rays. The conductivity increase after irradiation was measured as a function o f concentration, pH, temperature, metal cation content and additives. The conductivity increase could be shown to be due to the release o f associated counterions (N a+ or H+) as a result o f the formation o f chain breaks. At 28 mg I-1 D N A ~ 8 sodium ions are liberated per 100 eV absorbed energy (G (N a +) = 8.3). On the basis o f G value for single-strand breaks (ssb) o f G(ssb) = 0.55, it is calculated that 8.3/0.55 = 15 sodium ions per strand break are set free. The release o f N a+ monitored by 23N a-N M R at pH 7 as a function o f dose corresponds to that o f the conductivity increase. The rate o f the conductivity increase does not depend on d ose/p u lse (range 2 -2 0 J kg-1) and shows at least two components. The rate constant o f the fast and dom inant com ponent is constant above pH 8.5 (A: = 38 s— 1, 20 °C) and increases linearly with proton concentration below pH 7. Values o f 13kcal/m ol for the activation energy and 5 x 10" s_1 for the frequency factor were obtained at pH 7.3. Addition o f p-benzoquinone (pBQ) increases the rate constant o f the fast component proportionally to the concentration o f pBQ. From these results the rate-determining step o f the fast conductivity increase is concluded to be the splitting o f D N A radicals. The pH dependence and the m agnitude o f the activation energy agree with results from low molecular weight model com pounds for the C-4' m echanism ; this m echanism involves a heterolytic splitting o f the phosphoric acid ester bond starting from the 4' radical o f D N A . 
  Reference    Z. Naturforsch. 38c, 1030—1042 (1983); received Septem ber 19 1983 
  Published    1983 
  Keywords    DNA, Formation o f Strand Breaks, Electrical Conductivity, Pulse R adiolysis, Rate Constants 
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 TEI-XML for    default:Reihe_C/38/ZNC-1983-38c-1030.pdf 
 Identifier    ZNC-1983-38c-1030 
 Volume    38