REACTIVITY OF SINGLET OXYGEN TOWARD AMINO-ACIDS AND PEPTIDES
REACTIVITY OF SINGLET OXYGEN TOWARD AMINO-ACIDS AND PEPTIDES
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DOI：
10.1111/j.1751-1097.1994.tb05035.x
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发表时间：
1994-03-01
影响因子：
3.3
通讯作者：
FEITELSON, J
中科院分区：
文献类型：
--
作者：
MICHAELI, A;FEITELSON, J
本文研究了色氨酸、酪氨酸、组氨酸、蛋氨酸、半胱氨酸及其衍生物对D_2O-乙醇中单线态氧（O ~（-1（2）的猝灭作用。在我们的极性溶剂中，含有75%的D2 O的摩尔基础上，它被发现，（1）取代的芳香环吲哚，苯酚和咪唑的电子给甲基基团的总（即非反应性和反应性）猝灭速率常数增加了5至8倍。游离或封闭的氨基和羧基从环上除去两个亚甲基抵消了上述速率常数的增加。单线态氧的反应性猝灭，这导致芳环的氧化破坏，与上述取代效应相关。有人提出猝灭过程是通过O-1（2）与猝灭剂形成激基复合物而发生的。因此，我们的结果表明，氨基酸残基作为电子供体越好，与O-1（2）形成的激基复合物中的电荷转移贡献就越明显，就越有可能导致电荷分离，从而导致化学反应。(2)溶液中的寡肽或与氨基酸残基连接的肽键对单线态氧只有很小的影响。因此，可以预期蛋白质网络中的多肽链本身不会与存在的单个氧分子显著相互作用。后者的猝灭，在第一近似值下，应该仅取决于上述反应性氨基酸残基的存在及其对O-1（2）的可接近性，以及蛋白质结构内的有效介电常数。
Quenching of singlet oxygen (O-1(2)) in D2O-ethanol by the amino acids tryptophan, tyrosine, histidine, methionine, cysteine and their derivatives was measured by exciting the sensitizers rose bengal or meso-tetra (N-methyl-4-pyridyl)porphyrin tetratosylate in the presence of oxygen and the above quenchers in solution. In our polar solvent, containing 75% D2O on a molar basis it was found that (1) substitution of the aromatic ring in indole, phenol and imidazole by the electron-donating methyl group increases the total (i.e. nonreactive and reactive) quenching rate constant by a factor of five to eight. Free or blocked amino and carboxyl groups removed by two methylene groups from the ring counteract the above increase in the rate constant. The reactive quenching of singlet oxygen, which leads to oxidative destruction of the aromatic ring, correlates with the above substitution effects. It has been proposed that the quenching process takes place by formation of an exciplex between O-1(2) and the quencher. Thus our results indicate that the better an electron donor the amino acid residue is the more pronounced is the charge transfer contribution in the exciplex formed with O-1(2) and the more likely it is to lead to charge separation and hence to a chemical reaction. (2) Oligopeptides in solution or peptide bonds linked to the amino acid residue have only a minor effect on singlet oxygen. It can therefore be expected that the polypeptide chains per se in the protein network will not interact significantly with the single oxygen molecules present. The quenching of the latter should, to a first approximation, depend only on the presence of the above reactive amino acid residues and to their accessibility to O-1(2), as well as on the effective dielectric constant within the protein structure.