Radiation Laboratory, University of Notre Dame, Notre Dame, IN 46556, USA.
Amino Acids. 2012 Apr;42(4):1269-75. doi: 10.1007/s00726-010-0819-5. Epub 2010 Dec 5.
A slow, long range electron transfer (SLRET) in human serum albumin (HSA) is observed from an intact tyrosine (Tyr) residue to the neutral tryptophan (Trp) radical (Trp·) generated in pulse radiolysis. This radical is formed, at neutral pH, through oxidation with Br (2) (·-) radical anions of the single Trp 214 present. The SLRET rate constant of ~0.2 s(-1) determined is independent of HSA concentration and radiation dose, consistent with an intra-molecular process. This is the slowest rate constant so far reported for an intra-molecular LRET. In sharp contrast with the LRET reported for other proteins, the SLRET observed here is insensitive to oxygen, suggesting that the oxidized Trp is inaccessible to-or do not react with radiolytically generated O (2) (·-) . In N(2)O-saturated solutions, the SLRET is inhibited by Cu(2+) ions bound to the His 3 residue of the N-terminal group of HSA but it is partially restored in O(2)-saturated solutions.
在人类血清白蛋白（HSA）中观察到从完整的酪氨酸（Tyr）残基到脉冲辐射分解中产生的中性色氨酸（Trp）自由基（Trp·）的缓慢长程电子转移（SLRET）。在中性 pH 下，通过 present 存在的单个 Trp 214 的 Br（2）（·-）自由基阴离子氧化形成这种自由基。确定的~0.2 s（-1）的 SLRET 速率常数与 HSA 浓度和辐射剂量无关，与分子内过程一致。这是迄今为止报道的分子内 LRET 的最慢速率常数。与其他蛋白质报道的 LRET 形成鲜明对比的是，这里观察到的 SLRET 对氧气不敏感，这表明氧化的 Trp 无法接近或不与辐射产生的 O（2）（·-）反应。在 N（2）O 饱和溶液中，与 HSA 的 N 末端基团的 His 3 残基结合的 Cu（2+）离子抑制了 SLRET，但在 O（2）饱和溶液中部分恢复。
