Abstract：
Pulse radiolysis was employed to investigate fundamental radiation chemical reactions, which are essential in the radiation protection of DNA. Two positively charged peptides (PCPs), histidine-tyrosine-histidine (His-Tyr-His) and lysine-tyrosine-lysine (Lys-Tyr-Lys), as well as the amino acids that constitute them, were involved. The reaction rate constants for tyrosine (Tyr), histidine (His), lysine (Lys), His-Tyr-His, and Lys-Tyr-Lys with OH radicals (•OH) were (1.6 ± 0.3) × 1010, (9.0 ± 0.9) × 109, (1.4 ± 0.3) × 109, (1.8 ± 0.1) × 1010, and (1.0 ± 0.1) × 1010 M-1s-1, respectively, indicating that formation of peptide bond can affect the reaction of amino acids with •OH. Observed transient absorption spectra indicated a shielding effect of the His or Lys residues at both ends of the PCPs on the centrally located Tyr. The measurement of chemical repair capabilities using deoxyguanosine monophosphate (dGMP) as a model for DNA demonstrated that the reaction rate constants of Tyr, His-Tyr-His, and Lys-Tyr-Lys with dGMP radicals were (2.2 ± 0.5) × 108, (2.3 ± 0.1) × 108, and (3.3 ± 0.4) × 108 M-1s-1, respectively, implying that the presence of a positive charge may enhance the chemical repair process.
摘要：
脉冲辐射分解被用来研究基本的辐射化学反应，这对DNA的辐射防护至关重要。两个带正电荷的肽（PCPs），组氨酸-酪氨酸-组氨酸（His-Tyr-His）和赖氨酸-酪氨酸-赖氨酸（Lys-Tyr-Lys），以及构成它们的氨基酸，参与其中。酪氨酸（Tyr）的反应速率常数，组氨酸(His),赖氨酸(Lys),他的-提尔-他的,和具有OH自由基（•OH）的Lys-Tyr-Lys分别为（1.6±0.3）×1010，（9.0±0.9）×109，（1.4±0.3）×109，（1.8±0.1）×1010和（1.0±0.1）×1010M-1s-1，这表明肽键的形成可以影响氨基酸与·OH的反应。观察到的瞬时吸收光谱表明，PCP两端的His或Lys残基对位于中心的Tyr具有屏蔽作用。使用脱氧鸟苷一磷酸（dGMP）作为DNA模型的化学修复能力的测量表明，Tyr的反应速率常数，他的-提尔-他的,和具有dGMP基团的Lys-Tyr-Lys分别为（2.2±0.5）×108，（2.3±0.1）×108和（3.3±0.4）×108M-1s-1，这意味着正电荷的存在可以增强化学修复过程。
