Swarts S G, Sevilla M D
Department of Chemistry, Oakland University, Rochester, Michigan 48063.
Radiat Res. 1987 Oct;112(1):21-35.
The reactions of free and DNA-bound 2,2,5,5-tetramethylpyrrolidine-N-oxyl (PROXYL) probes with radicals generated during radiolysis of dilute aqueous solutions of DNA were examined. For the free PROXYL probe in deaerated solution with each of the four nucleotides (dAMP, dCMP, dGMP, and TMP) it was found that the pyrimidine radicals were more reactive toward the probe than were the purine radicals. Reactions of the electron adduct of TMP and the hydroxyl radical adducts of dAMP, dGMP, and TMP with the probe resulted in little or no reduction of the probe. For TMP these results are consistent with the fact that both the protonated electron and hydroxyl radical adducts of TMP will covalently bind to the nitroxide function of the probe. Reduction of the PROXYL probe was observed in reactions with the hydroxyl radical adduct of dCMP and with the electron adducts of dAMP, dCMP, and dGMP. Results of the radiolysis of the free PROXYL probe in deaerated dilute solution of DNA suggest that the PROXYL probe protects the DNA from water radical attack as the ratio of DNA bases to PROXYL probe increases above 50:1. Reactions of DNA-bound probes are dependent on the depth of the nitroxide function in relation to the major groove of the DNA helix. Two probes with tether lengths which are less than the depth of the major groove show an expected increase in reactions with DNA base radicals as compared to a probe with a tether that extends beyond the groove. The longer probe is involved largely in reactions with sugar and water radicals along the periphery of the DNA helix. In the presence of oxygen, there is a dramatic decrease in the loss of both the free and DNA-bound probes due to the lack of reaction of these probes with peroxyl radicals formed by the addition of molecular oxygen to DNA radicals.
研究了游离态及与DNA结合的2,2,5,5-四甲基吡咯烷-N-氧基（PROXYL）探针与DNA稀水溶液辐射分解过程中产生的自由基的反应。对于在脱氧溶液中与四种核苷酸（dAMP、dCMP、dGMP和TMP）中的每一种共存的游离PROXYL探针，发现嘧啶自由基对该探针的反应性比嘌呤自由基更高。TMP的电子加合物以及dAMP、dGMP和TMP的羟基自由基加合物与该探针的反应导致该探针几乎没有减少或没有减少。对于TMP，这些结果与以下事实一致：TMP的质子化电子加合物和羟基自由基加合物都会与该探针的氮氧化物官能团共价结合。在与dCMP的羟基自由基加合物以及dAMP、dCMP和dGMP的电子加合物的反应中观察到PROXYL探针减少。在脱氧DNA稀溶液中游离PROXYL探针的辐射分解结果表明，当DNA碱基与PROXYL探针的比例增加到50:1以上时，PROXYL探针可保护DNA免受水自由基攻击。与DNA结合的探针的反应取决于氮氧化物官能团相对于DNA螺旋大沟的深度。与连接链延伸超出沟槽的探针相比，连接链长度小于大沟深度的两种探针与DNA碱基自由基的反应预期会增加。较长的探针主要参与与DNA螺旋外围的糖自由基和水自由基的反应。在有氧存在的情况下，游离和与DNA结合的探针的损失都急剧减少，这是因为这些探针与DNA自由基与分子氧加成形成的过氧自由基不发生反应。
