PULSE RADIOLYTIC MEASUREMENT OF REDOX POTENTIALS - THE TYROSINE AND TRYPTOPHAN RADICALS
PULSE RADIOLYTIC MEASUREMENT OF REDOX POTENTIALS - THE TYROSINE AND TRYPTOPHAN RADICALS
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DOI：
10.1021/bi00437a049
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发表时间：
1989-05-30
期刊：
影响因子：
2.9
通讯作者：
KLAPPER, MH
中科院分区：
文献类型：
--
作者：
DEFELIPPIS, MR;MURTHY, CP;KLAPPER, MH
俄亥俄州哥伦布市俄亥俄州立大学化学系生物化学系和以色列比尔谢瓦84190内盖夫核研究中心化学系1988年12月1日成立；摘要：采用脉冲辐射解法测定了色氨酸侧链中性吲哚基自由基（1.05±0.01 V vs NHE, pH 7.0和25 C）和酪氨酸侧链中性苯氧基自由基（0.94±0.01 V vs NHE, pH 7.0和25 C）的氧化还原中点电位。这些电位是通过使用各种无机对照化合物在动力学和平衡协议中获得的。我们将这些结果与文献中已有的结果进行了比较，并提供了在0.42-1.28 v范围内建立脉冲辐射分解氧化还原参考标度的有用数据。通常，酪氨酸侧链（tyrO'） 1的短寿命苯氧基在细菌的i-核糖核苷酸还原酶中是一种稳定的物种，并且是该酶活性所必需的（Reichard & Ehrenberg, 1983）。这种相同的自由基最近被认为与光系统II对水的氧化有关（Barry & Babcock, 1987）。我们对tyrO‘的兴趣源于对蛋白质和多肽的1电子分子内远程电子转移的观察（Priitz & Land, 1979； Priitz等人，1980,1981；Faraggi等人，1989a）： trp’ -tyrOH-trpH-tyrO '(1) tyrOH-trp' -tyrO' - trphn在这些反应中，色氨酸侧链中性吲酚自由基（trp‘）氧化酪氨酸侧链苯酚（tyrOH）形成色氨酸（trpH）和tyrO’。[在eq 1中，我们指出了肽中酪氨酸和色氨酸顺序颠倒的反应，因为我们发现顺序会影响电子转移速率（Faraggi et al., 1989a）。]虽然这种氧化还原反应尚不清楚是否会自然发生（也没有发现色氨酸自由基在自然界中的作用），但它是最近在蛋白质中研究的许多分子内电子转移之一
Division of Biological Chemistry, Department of Chemistry, The Ohio State University, Columbus, Ohio 43210, and Department of Chemistry, Nuclear Research Centre—Negev, Beer-Sheva 84190, Israel Received December 1, 1988; Revised Manuscript Received February 17, 1989 abstract: With the technique of pulse radiolysis we have measured the redox midpoint potentials of the tryptophan side chain neutral indolyl radical (1.05±0.01 V vs NHE, pH 7.0 and 25 C) and the tyrosine side chain neutral phenoxy radical (0.94±0.01 vs NHE, pH 7.0 and 25 C). These potentials were obtained by using a variety of inorganic reference compounds in both kinetic and equilibrium protocols. We compare these results with others already in the literature, and we also present data useful in establishing a pulse radiolysis redox reference scale over the range 0.42-1.28 V. e normally short lived phenoxy radical of the tyrosine side chain (tyrO') 1 is found as a stable species in a bacterial ri-bonucleotide reductase and is required for that enzyme’s ac-tivity (Reichard & Ehrenberg, 1983). This same radical has been implicated recently in the oxidation of water by photo-system II (Barry & Babcock, 1987). Our interest in tyrO'stems from theobservation in proteins and polypeptides (Priitz & Land, 1979; Priitz et al., 1980, 1981; Faraggi et al., 1989a) of the 1-electron intramolecular long-range electron transfers: trp'-tyrOH—trpH-tyrO'(1) tyrOH-trp'—tyrO'-trpHIn these reactions thetryptophan side chain neutral indolyl radical (trp') oxidizes the tyrosine side chain phenol (tyrOH) to form tryptophan (trpH) and tyrO'.[In eq 1 we have in-dicated the reactions with the order of tyrosine and tryptophan reversed in the peptide, since we have found that the order can affect the electron-transfer rate (Faraggi et al., 1989a).] While this redox reaction is not known to occur naturally (and no role has yet been uncovered in nature for the tryptophan radical), it is one of a number of intramolecular electron transfers that have been recently studied in proteins, poly-