Radiation-chemical Discussion on Inverse Dose-rate Effect Observed in Radiation-induced Strand Breaks of Plasmid DNA

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Experimental results of inverse dose-rate effect, so-called Kada Effects, which was published by Takakura and her coworkers on radiation-induced strand breaks of plasmid DNA in aerated aqueous solution, have been kinetically analyzed and discussed on the basis of radiation chemistry. the kinetic analysis indicates that there are two possible mechanisms; 1) equilibrium mixture of O2- and HO2 is responsible for strand breaks of DNA, and 2) peroxyl radical produced from citrate is effective for the strand breaks. However, the detailed kinetic analysis revealed that the latter is improbable because unimolecular decay of the peroxyl radical must be assumed to be negligible for its participation despite fast decay of analogous organic peroxyl radicals. The analysis has also given 9.93 ± 0.10 dm^3 mol^<-1> s^<-1> per nucleotide unit, which corresponds to 7.62x 1O^4 dm^3 mol^<-1> s^<-1> per DNA molecule, as the rate constant for the reaction of the equilibrium mixture with plasmid pBR 322 DNA. Furthermoer the probability that the reaction of the mixture with a nucleotide unit of DNA leads to strand breaks was obtained to be 3.36x 10^<-3> for gamma-irradiated system and 1.98 x 10^<-3> for beta-irradiated system, respectively.
日本放射線影響学会の論文