D. Becker et al., INFLUENCE OF OXYGEN ON THE REPAIR OF DIRECT-RADIATION DAMAGE TO DNA BY THIOLS IN MODEL SYSTEMS, International journal of radiation biology, 65(5), 1994, pp. 537-548
Citations number
71
Categorie Soggetti
Radiology,Nuclear Medicine & Medical Imaging","Nuclear Sciences & Tecnology
Here the reactions of thiols with DNA primary radical intermediates fo
rmed after gamma-irradiation of frozen (77 K) anoxic and oxic solution
s of DNA/thiol mixtures are investigated. Through analysis of the expe
rimental composite spectra at each annealing temperature, the relative
concentrations of individual radicals present are estimated and react
ion sequences inferred. In all samples the primary DNA radical anions
and cations (DNA(.+) and DNA(.-)) are suggested to be the predominant
radicals at low temperatures. In anoxic samples, TH. (5,6-dihydrothym-
5-yl radical), RSSR(.-) and, in glutathione samples, (.)GSH [gamma-glu
-NHC(CH2SH) CO-gly] radicals are observed as the temperature is increa
sed. The presence of oxygen efficiently suppresses the formation of RS
SR(.-) and (.)GSH; instead, in oxic samples, O-2(.-), DNAOO(.), RSOO(.
) and RSO(.) are observed at higher temperatures. The photolytic conve
rsion of RSOO(.) to RSO(2)(.) is used to verify the presence of RSOO(.
) in gamma-irradiated DNA/thiol systems and confirm that the computer
analysis employed yields reasonable estimates of the relative DNAOO(.)
and RSOO(.) concentrations. From the relative concentrations of radic
als present, it is clear that the radicals observed at higher temperat
ures originate from the radical reactions of the primary DNA(.+) and D
NA(.-) radicals. Based on the reaction sequences inferred and previous
work with thiols alone, it is concluded that TH., DNAOO(.) and RSOO(.
) (in part) originate largely with DNA(.-), whereas RSSR(.-), (.)GSH a
nd RSOO(.) (in part) originate largely with DNA(.+). The possible role
s of DNAOO(.), RSOO(.), RSO(.), RSO(2)(.) and (.)OOGSH in the chemical
oxygen enhancement effect at biologically realistic temperatures are
discussed.