Milligan J R, Ng J Y, Wu C C, Aguilera J A, Ward J F, Kow Y W, Wallace S S, Cunningham R P
Department of Radiology, University of California at San Diego, La Jolla 92093-0610, USA.
Radiat Res. 1996 Oct;146(4):436-43.
Using agarose gel electrophoresis, we have measured the yields of DNA single-strand breaks (SSBs) for plasmid DNA gamma-irradiated in aerobic aqueous solution. Incubation after irradiation with the base damage repair endonucleases formamidopyrimidine-DNA N-glycosylase (FPG) or endonuclease III (endo III) results in an increase in the yield of SSBs. In the absence of dimethyl sulfoxide (DMSO) during irradiation, this increase is consistent with the yields of known substrates for FPG and endo III as determined by gas chromatography/mass spectrometry. After irradiation in the presence of 1 mol dm-3 DMSO, the increase in the yield of SSBs after enzyme incubation was further enhanced by a factor of about 5 to 7. The magnitude of this effect, the inability of acrylamide or oxygen to suppress it, and its attenuation by N,N,N',N'-tetramethylphenylenediamine (TMPD) or glycerol all suggest that the methylperoxyl radical (derived from DMSO) is involved as an intermediate. Reactions of the methylperoxyl radical (or some other species derived from it) do not result in strand break damage, but are responsible for DNA base damages which are recognized by FPG and endo III.
我们使用琼脂糖凝胶电泳法测定了在有氧水溶液中经γ射线辐照的质粒DNA的单链断裂（SSB）产率。用碱基损伤修复内切酶甲酰胺嘧啶-DNA N-糖基化酶（FPG）或内切酶III（endo III）辐照后孵育，会导致SSB产率增加。在辐照过程中不存在二甲基亚砜（DMSO）时，这种增加与通过气相色谱/质谱法测定的FPG和endo III已知底物的产率一致。在1 mol dm⁻³ DMSO存在下辐照后，酶孵育后SSB产率的增加进一步提高了约5至7倍。这种效应的大小、丙烯酰胺或氧气无法抑制它以及其被N，N，N'，N'-四甲基对苯二胺（TMPD）或甘油减弱，都表明甲基过氧自由基（源自DMSO）作为中间体参与其中。甲基过氧自由基（或由其衍生的某些其他物质）的反应不会导致链断裂损伤，但会导致DNA碱基损伤，这些损伤可被FPG和endo III识别。
