Washino K, Katsikas L, Schnabel W
Int J Radiat Biol Relat Stud Phys Chem Med. 1984 Dec;46(6):747-58. doi: 10.1080/09553008414551981.
Poly(riboadenylic acid) was irradiated in N2O-saturated dilute aqueous solution at pH 7.8 with single pulses (50-200 ns) of 16 MeV electrons. With the aid of Rayleigh light scattering measurements both the extent and rate of main-chain scission were measured in the absence and the presence of cysteamine (RSH). In both cases two modes of light scattering intensity (LSI) decrease were detected. From this finding it was concluded that two chemically different radical sites, giving rise to main-chain breakage, were produced by OH attack on the macromolecules. Cysteamine reduced the extent of LSI decrease and accelerated the rate of the slow mode of LSI decrease significantly. The fast mode of the LSI decrease is due to fragment diffusion and therefore the influence of cysteamine on the rate of decay of the short-lived radical could not be studied. The assessment of the relative importance of .OH scavenging (RSH + .OH----RS. + H2O) and of repair (PA. + RSH----PAH + RS.) with respect to protection yielded the following: in the case of the long-lived radical, repair contributes significantly at low RSH concentration (less than 10(-4) M); in the case of the short-lived radical, OH scavenging dominates and repair becomes noticeable only at [RSH] greater than 10(-4)M. The following data were evaluated in this work: 100 eV-yield of main-chain scission, G(sb) = 1.1; lifetimes of radicals: less than 50 microseconds (short-lived), 0.6 s (long-lived), kPA. + RSH = 3.4 X 10(6)M-1 S-1 (for long-lived radicals).
在pH值为7.8的N₂O饱和稀水溶液中，用16兆电子伏特电子的单脉冲（50 - 200纳秒）辐照聚（核糖核酸）。借助瑞利光散射测量，在不存在和存在半胱胺（RSH）的情况下，测量了主链断裂的程度和速率。在这两种情况下，均检测到光散射强度（LSI）下降的两种模式。由此发现得出结论，OH对大分子的攻击产生了两个化学性质不同的自由基位点，导致主链断裂。半胱胺降低了LSI下降的程度，并显著加速了LSI下降慢模式的速率。LSI下降的快模式是由于片段扩散，因此无法研究半胱胺对短寿命自由基衰减速率的影响。关于保护作用，对.OH清除（RSH +.OH→RS. + H₂O）和修复（PA. + RSH→PAH + RS.）的相对重要性评估得出以下结果：对于长寿命自由基，在低RSH浓度（小于10⁻⁴M）时，修复起显著作用；对于短寿命自由基，OH清除起主导作用，只有当[RSH]大于10⁻⁴M时，修复才变得明显。在这项工作中评估了以下数据：主链断裂的100电子伏特产额，G(sb) = 1.1；自由基寿命：小于50微秒（短寿命），0.6秒（长寿命），kPA. + RSH = 3.4×10⁶M⁻¹S⁻¹（对于长寿命自由基）。
