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内容記述 |
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 histidine (His), tyrosine (Tyr), lysine (Lys), His-Tyr-His, and Lys-Tyr-Lys with OH radicals (?OH) were (9.0 ± 0.9) × 109, (1.6 ± 0.3) × 1010, (1.4 ± 0.3) × 109, (1.8 ± 0.3) × 109, 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 (2.4 ± 0.3) × 108, (2.3 ± 0.4) × 108, and (3.4 ± 0.9) × 108 M?1s?1, respectively, implying that the presence of a positive charge may enhance the chemical repair process. |
