Tomita H, Kai M, Kusama T, Aoki Y, Ito A
Department of Radiological Health, Faculty of Medicine, University of Tokyo, Japan.
Int J Radiat Biol. 1994 Dec;66(6):669-82.
A new theoretical model for estimating yield of initial DNA strand break induced by several monoenergetic electrons is presented. It is based on the Monte Carlo track structure simulation and on new DNA structure models (one turn of double-strand DNA, nucleosome, solenoid), and links physical and chemical stages of radiation action. Direct and indirect effects are strictly distinguished. Some results of calculations indicated: (1) the number of single strand breaks per nucleus (6 microns in diameter) per Gy in pure water was about 10 times that in a cell environment (OH radical life time is assumed to be 8.7 ns). This is due to the difference in the time-dependent variation in the total number of the OH radical; and (2) the contribution of indirect effects to total damage decreased as the order of the DNA target model structure used in the stimulation increased (e.g. a one-turn model of double-strand DNA, approximately 98.4%; but the 30-nm solenoid model, approximately 86.1%). This was due to the protective effect of histone protein against OH radical attack. Double-strand breaks were scored if two single-strand breaks were located on the same base pair. The present study indicated that the information from morphological and biochemical examinations of the cell environment must be considered more carefully with computer simulation.
提出了一种新的理论模型，用于估算几种单能电子诱导的初始DNA链断裂产额。该模型基于蒙特卡罗径迹结构模拟和新的DNA结构模型（双链DNA的一圈、核小体、螺线管），并将辐射作用的物理和化学阶段联系起来。直接效应和间接效应被严格区分。一些计算结果表明：（1）在纯水中，每戈瑞每细胞核（直径6微米）的单链断裂数约为细胞环境中的10倍（假设OH自由基寿命为8.7纳秒）。这是由于OH自由基总数随时间变化的差异；（2）随着模拟中使用的DNA靶标模型结构顺序增加，间接效应占总损伤的比例降低（例如，双链DNA的一圈模型，约为98.4%；但30纳米螺线管模型，约为86.1%）。这是由于组蛋白对OH自由基攻击的保护作用。如果两个单链断裂位于同一碱基对上，则计为双链断裂。本研究表明，在计算机模拟中必须更仔细地考虑来自细胞环境形态学和生物化学检查的信息。
