Frankenburg-Schwager M, Harbich R, Beckonert S, Frankenberg D
University of Göttingen, Abtlg. Klinikum Strahlenbiologie und Klinikum Strahlenphysik, Germany.
Int J Radiat Biol. 1994 Nov;66(5):543-7. doi: 10.1080/09553009414551591.
Yeast cells in stationary phase were exposed under oxic or anoxic conditions to sparsely (30 MeV electrons) or densely (3.5 MeV alpha-particles) ionizing radiation. For all four experimental set-ups postirradiation treatment of cells was the same, i.e. cells were kept under oxic conditions in non-growth medium at 30 degrees C. Double-strand break (dsb) rejoining was measured during this treatment yielding the following results: (1) half-life values ranged from < 60 min (electrons, anoxia) to 3.8 h (low doses of electrons, oxia), 7 h (alpha-particles, anoxia), 10 h (high doses of electrons, oxia) and 13 h (alpha-particles, oxia). (2) In the case of exposure of oxic cells to electrons a biphasic rejoining kinetics is observed with a dose-dependent increase of the fraction of the slow component. These results suggest that half-life values of dsb rejoining in a given cell depend on physical, chemical and biological parameters. The rejoining of dsb slows down with increasing LET, being probably due to the increasing complexity of dsb. Oxygenation of cells at the time of irradiation affects half-life values, indicating that radiation chemistry plays an important role. The biphasic rejoining kinetics observed for dsb induced by electrons in oxic cells is interpreted in terms of a dose-dependent change of chromatin structure hindering the interaction between damaged chromatin and the rejoining enzymes rather than by two chemically distinct types of dsb with differing half-life values.
将处于稳定期的酵母细胞在有氧或无氧条件下暴露于稀疏（30 MeV电子）或密集（3.5 MeVα粒子）电离辐射中。对于所有四种实验设置，细胞的辐照后处理是相同的，即细胞在30℃的非生长培养基中保持在有氧条件下。在该处理过程中测量双链断裂（dsb）的重新连接，得到以下结果：（1）半衰期值范围从<60分钟（电子，无氧）到3.8小时（低剂量电子，有氧）、7小时（α粒子，无氧）、10小时（高剂量电子，有氧）和13小时（α粒子，有氧）。（2）在有氧细胞暴露于电子的情况下，观察到双相重新连接动力学，慢组分的比例随剂量增加。这些结果表明，给定细胞中dsb重新连接的半衰期值取决于物理、化学和生物学参数。随着传能线密度（LET）增加dsb的重新连接减慢，这可能是由于dsb的复杂性增加。辐照时细胞的氧合作用影响半衰期值，表明辐射化学起重要作用。在有氧细胞中由电子诱导的dsb观察到的双相重新连接动力学，根据染色质结构的剂量依赖性变化来解释，这种变化阻碍了受损染色质与重新连接酶之间的相互作用，而不是由具有不同半衰期值的两种化学性质不同的dsb类型导致的。
