Deeg K J, Katsikas L, Schnabel W
Int J Radiat Biol Relat Stud Phys Chem Med. 1987 Mar;51(3):527-40. doi: 10.1080/09553008714551001.
Histone H2B from calf thymus was irradiated with 50 or 100 ns pulses of 16 MeV electrons in N2O-saturated aqueous solution at pH 9 in the presence of NaN3. All tyrosine moieties in the histone were found to be freely accessible to the attack of .N3 radicals (formed by the reaction .OH + N3(-)----OH- + .N3). At sufficiently high concentrations of H2B, tyrosyl radicals were formed with G(TyrO.) = 5.4/100 eV and dityrosine groups with G(dityr) = 1.6/100 eV, indicating that about 60 per cent of tyrosyl radicals formed bisphenolic products. There is no polymer effect with respect to G(dityr) as inferred from comparison with other authors' data obtained with low molecular weight compounds. Kinetic measurements revealed that tyrosyl radicals reacted in two modes, a fast one with a value of tau 1/2 of about several milliseconds and a slow second order process also in the millisecond range. The fast process is assigned to intramolecular reactions of tyrosyl radicals generated in close proximity to each other and the slow process to intermolecular self reactions of isolated tyrosyl radicals distributed statistically in the solution. There is a polymer effect with respect to the rate constant of the slow process: 2k8 = 4.8 X 10(7) dm3 mol-1 s-1 (H2B) and 2k8 = 4 X 10(8) dm3 mol-1 s-1 (Lys-Tyr-Lys, Prütz et al. (1983)). The five histones contained in calf thymus were isolated chromatographically with the aid of two gels, Bio-Gel P-60 (BioRad) and Sephadex G100 (Pharmacia).
在pH 9的N₂O饱和水溶液中，于NaN₃存在的情况下，用16 MeV电子的50或100 ns脉冲辐照来自小牛胸腺的组蛋白H2B。发现组蛋白中的所有酪氨酸部分都可被·N₃自由基（由反应·OH + N₃⁻→OH⁻ + ·N₃形成）自由攻击。在足够高浓度的H2B时，形成了G(TyrO·)=5.4/100 eV的酪氨酸自由基和G(dityr)=1.6/100 eV的二酪氨酸基团，这表明约60%的酪氨酸自由基形成了双酚类产物。与其他作者用低分子量化合物获得的数据比较可知，对于G(dityr)不存在聚合物效应。动力学测量表明，酪氨酸自由基以两种模式反应，一种快速反应，其τ₁/₂值约为几毫秒，另一种慢二级过程也在毫秒范围内。快速过程归因于彼此紧邻产生的酪氨酸自由基的分子内反应，而慢过程归因于在溶液中统计分布的孤立酪氨酸自由基的分子间自反应。对于慢过程的速率常数存在聚合物效应：2k₈ = 4.8×10⁷ dm³ mol⁻¹ s⁻¹（H2B）和2k₈ = 4×10⁸ dm³ mol⁻¹ s⁻¹（Lys-Tyr-Lys，Prütz等人，(1983)）。借助两种凝胶Bio-Gel P-60（BioRad）和Sephadex G100（Pharmacia）通过色谱法分离小牛胸腺中所含的五种组蛋白。
