Nitric Oxide And The Metabolism Of Toxic Chemicals/Drugs

蛋白质硝基酪氨酸含量的测定已成为检测组织氧化损伤的常用技术。蛋白质硝化被认为是一氧化氮(NO)与氧衍生物种(如超氧化物)反应生成高活性氮氧化物中间体(如过氧亚硝酸盐)的最终产物。前列腺素H合成酶-2(PHS-2)在其催化前列腺素形成的过程中形成一个或多个酪氨酸自由基。在NO生成剂月桂酸二乙胺存在下，PHS-2衍生的酪氨酸自由基的电子自旋共振谱被另一个含有氮原子的自由基光谱取代，这表明PHS-2的活性不依赖于NO。后者中氮的超精细耦合常数的大小明确地表明它是亚氨氧基自由基，它可能是由亚硝基酪氨酸氧化形成的，亚硝基酪氨酸是没有酪氨酸自由基加成的稳定产物。超氧化物歧化酶的加入没有改变光谱，表明过氧亚硝酸盐没有参与。暴露于NO生成物后的PHS-2的Western印迹分析显示有硝基酪氨酸的形成。该结果为依赖一氧化氮的酪氨酸硝化提供了一种机制，不需要形成更高活性的氮氧化物中间体，如过氧亚硝酸盐或二氧化氮。

The determination of protein nitrotyrosine content has become a frequently used technique for the detection of oxidative tissue damage. Protein nitration has been suggested to be a final product of the production of highly reactive nitrogen oxide intermediates (e.g. peroxynitrite) formed in reactions between nitric oxide ( NO) and oxygen-derived species such as superoxide. The enzyme prostaglandin H synthase-2 (PHS-2) forms one or more tyrosyl radicals during its enzymatic catalysis of prostaglandin formation. In the presence of the NO-generator diethylamine nonoate, the electron spin resonance spectrum of the PHS-2-derived tyrosyl radical is replaced by the spectrum of another free radical containing a nitrogen atom inspite of the fact the PHS-2 activity is independent of NO. The magnitude of the nitrogen hyperfine coupling constant in the latter species unambiguously identifies it as an iminoxyl radical, which is likely formed by the oxidation of nitrosotyrosine, a stable product of the addition of NO tyrosyl radical. Addition of the superoxide dismutase did not alter the spectra, indicating that peroxynitrite was not involved. Western blot analysis of PHS-2 after exposure to the NO-generator revealed nitrotyrosine formation. The results provide a mechanism for nitric oxide-dependent tyrosine nitration that does not require formation of more highly reactive nitrogen oxide intermediates such as peroxynitrite or nitrogen dioxide.