Tanner C, Navaratnam S, Parsons B J
The Multidisciplinary Research and Innovation Centre, The North East Wales Institute, Plas Coch, Wrexham, UK.
Free Radic Biol Med. 1998 Mar 1;24(4):671-8. doi: 10.1016/s0891-5849(97)00340-7.
The technique of pulse radiolysis has been used to investigate the possibility of intramolecular charge transfer in the dipeptide histidyltyrosine, following one-electron oxidation of one of its amino acid residues. The radical anion, Br2.- was found to react with the dipeptide at pH 6.0 with a bimolecular rate constant of 2.3+/-0.2 x 10(7) dm3 mol(-1)s(-1) suggesting that it reacts very selectively with the histidine moiety. Spectral observations at, or close to the end of this reaction show only the presence of a tyrosinyl free radical (TyrO.), however, indicating that fast (>10(6) s(-1) intramolecular charge transfer has taken place between histidine radicals (His+.) and tyrosine (TyrOH). This finding was supported by the direct observation of the rate of formation of TyrO. in experiments with the free amino acids, histidine and tyrosine, under conditions where Br2.- reacted selectively with histidine. The bimolecular rate constant for the reaction between His+. and TyrOH was found to be 2.4+/-0.5 x 10(6) dm3 mol(-1)s(-1). Taken together, the results of the study indicate that His+. is a relatively strong oxidising agent where (E (His+./His) > 770 mV at pH 6.0.
脉冲辐解技术已被用于研究二肽组氨酰酪氨酸在其一个氨基酸残基单电子氧化后发生分子内电荷转移的可能性。发现自由基阴离子Br₂⁻在pH 6.0时与该二肽反应，双分子速率常数为2.3±0.2×10⁷ dm³ mol⁻¹ s⁻¹，这表明它与组氨酸部分反应具有很高的选择性。然而，在该反应接近尾声或反应结束时的光谱观察仅显示存在酪氨酸自由基（TyrO.），这表明在组氨酸自由基（His⁺.）和酪氨酸（TyrOH）之间发生了快速（>10⁶ s⁻¹）的分子内电荷转移。在Br₂⁻与组氨酸选择性反应的条件下，用游离氨基酸组氨酸和酪氨酸进行实验时对TyrO.形成速率的直接观察支持了这一发现。发现His⁺.与TyrOH反应的双分子速率常数为2.4±0.5×10⁶ dm³ mol⁻¹ s⁻¹。综合来看，该研究结果表明His⁺.是一种相对较强的氧化剂，在pH 6.0时（E(His⁺./His)>770 mV）。
