KINETICS OF SUPEROXIDE DISMUTASE-CATALYZED AND IRON-CATALYZED NITRATION OF PHENOLICS BY PEROXYNITRITE
KINETICS OF SUPEROXIDE DISMUTASE-CATALYZED AND IRON-CATALYZED NITRATION OF PHENOLICS BY PEROXYNITRITE
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DOI：
10.1016/0003-9861(92)90432-v
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发表时间：
1992-11-01
影响因子：
3.9
通讯作者：
TSAI, M
中科院分区：
文献类型：
--
作者：
BECKMAN, JS;ISCHIROPOULOS, H;TSAI, M
超氧化物歧化酶和Fe 3 +EDTA催化过氧化亚硝酸根（ONOO−）硝化包括蛋白质中酪氨酸在内的各种酚类化合物。硝化不介导的自由基机制，因为羟基自由基清除剂不减少超氧化物歧化酶或Fe 3 + EDTA催化的硝化和二氧化氮是不是一个显着的产品从任何催化剂。相反，金属离子似乎催化过氧亚硝酸盐的异裂，形成硝态氮（NO2+）。在pH7.0时，过氧亚硝酸分解为氢氧根离子和硝鎓离子的能量为13 kcal · mol− 1。Fe 3 +EDTA催化硝化反应的活化能为12 kcal · mol− 1，反应速率为5700 m −1· s− 1，反应温度为37 °C，pH值为7.5。在低浓度下，过氧亚硝酸根与牛Cu，Zn超氧化物歧化酶的反应速率为105 m-1· s-1，但当超氧化物歧化酶浓度超过10 μ m时，硝化速率不再受超氧化物歧化酶浓度的影响，只有9%的过氧亚硝酸根生成硝基苯酚。我们认为，过氧亚硝基阴离子在同构象中更稳定，而在反构象中只有更高能量的物种才能适合Cu，Zn超氧化物歧化酶的活性中心。在高浓度的超氧化物歧化酶，酚硝化可能是有限的异构化率从thecistotransformations的过氧亚硝酸盐，以及竞争途径过氧亚硝酸盐分解。相反，Fe 3 +EDTA似乎直接与该阴离子反应，导致更高的硝化产率。
Superoxide dismutase and Fe3+EDTA catalyzed the nitration by peroxynitrite (ONOO−) of a wide range of phenolics including tyrosine in proteins. Nitration was not mediated by a free radical mechanism because hydroxyl radical scavengers did not reduce either superoxide dismutase or Fe3+EDTA-catalyzed nitration and nitrogen dioxide was not a significant product from either catalyst. Rather, metal ions appear to catalyze the heterolytic cleavage of peroxynitrite to form a nitronium-like species (NO2+). The calculated energy for separating peroxynitrous acid into hydroxide ion and nitronium ion is 13 kcal · mol−1at pH 7.0. Fe3+EDTA catalyzed nitration with an activation energy of 12 kcal · mol−1at a rate of 5700m−1· s−1at 37 °C and pH 7.5. The reaction rate of peroxynitrite with bovine Cu,Zn superoxide dismutase was 105m−1· s−1at low superoxide dismutase concentrations, but the rate of nitration became independent of superoxide dismutase concentration above 10 μmwith only 9% of added peroxynitrite yielding nitrophenol. We propose that peroxynitrite anion is more stable in thecisconformation, whereas only a higher energy species in thetransconformation can fit in the active site of Cu,Zn superoxide dismutase. At high superoxide dismutase concentrations, phenolic nitration may be limited by the rate of isomerization from thecistotransconformations of peroxynitrite as well as by competing pathways for peroxynitrite decomposition. In contrast, Fe3+EDTA appears to react directly with thecisanion, resulting in greater nitration yields.