Becker D, Razskazovskii Y, Callaghan M U, Sevilla M D
Department of Chemistry, Oakland University, Rochester, Michigan 48309, USA.
Radiat Res. 1996 Oct;146(4):361-8.
The free radicals produced from the irradiation of hydrated DNA with a heavy-ion beam have been investigated by ESR spectroscopy. The dominant free radical species formed after 60 MeV/nucleon (16)O(8+) ion-beam irradiations at low temperatures (77 K) are the same as those previously identified from studies using low-LET radiation, pyrimidine electron-gain radicals and purine electron-loss radicals; however, greater relative amounts of neutral carbon-centered radicals are found with the higher-LET radiation, and a new phosphorus-centered radical is identified. The fraction of neutral carbon radicals is also found to increase along the ion-beam track with the highest amounts found in the Bragg peak. The neutral carbon-centered radicals likely arise in part from the sugar moiety. The G values found for total trapped radicals at 77 K are significantly smaller for the (16)O(8+) ion beam than those found for low-LET radiation. The new phosphorus-centered radical species is identified by its large 31P parallel hyperfine coupling of about 780 G as a phosphoryl radical. This species is produced linearly with dose and is not found in significant amounts in DNA irradiated with low-LET radiation. The phosphoryl radical must be produced by the fragmentation of a P-O bond and suggests the possibility of a direct strand break. The yield of phosphoryl species is small (about 0.1% of all radicals); however, it clearly indicates that new mechanisms of damage which are not significant for low-LET radiation must be considered for high-LET radiation.
利用电子自旋共振光谱法研究了重离子束辐照水合DNA产生的自由基。在低温（77K）下，60 MeV/核子的(16)O(8+)离子束辐照后形成的主要自由基种类与先前使用低传能线密度辐射研究中确定的相同，即嘧啶电子俘获自由基和嘌呤电子丢失自由基；然而，在高传能线密度辐射下发现中性碳中心自由基的相对含量更高，并且鉴定出一种新的磷中心自由基。还发现中性碳自由基的比例沿离子束轨迹增加，在布拉格峰处含量最高。中性碳中心自由基可能部分源自糖部分。在77K下，(16)O(8+)离子束产生的总俘获自由基的G值明显小于低传能线密度辐射的G值。新的磷中心自由基种类通过其约780G的大31P平行超精细偶合被鉴定为磷酰基自由基。该种类随剂量线性产生，在用低传能线密度辐射辐照的DNA中未大量发现。磷酰基自由基一定是由P-O键断裂产生的，这表明可能存在直接的链断裂。磷酰基种类的产率很小（约占所有自由基的0.1%）；然而，它清楚地表明，对于高传能线密度辐射，必须考虑低传能线密度辐射中不显著的新损伤机制。
