Oxidations of N(omega)-hydroxyarginine analogues and various N-hydroxyguanidines by NO synthase II: key role of tetrahydrobiopterin in the reaction mechanism and substrate selectivity.
Oxidations of N(omega)-hydroxyarginine analogues and various N-hydroxyguanidines by NO synthase II: key role of tetrahydrobiopterin in the reaction mechanism and substrate selectivity.
复制标题
NO 合酶 II 氧化 N(omega)-羟基精氨酸类似物和各种 N-羟基胍：四氢生物蝶呤在反应机制和底物选择性中的关键作用。
DOI：
10.1021/tx0001068
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发表时间：
2001
影响因子：
4.1
通讯作者：
Mansuy,D
中科院分区：
文献类型：
--
作者：
Moali,C;Boucher,JL;Renodon-Corniere,A;Stuehr,DJ;Mansuy,D
L-精氨酸2、高-L-精氨酸1及其N ω-羟基衍生物4和3的氧化（分别为NOHA和homo-NOHA）和四种N-羟基胍，Nω-羟基降-l-精氨酸5（nor-NOHA），Nω-羟基二去甲-l-精氨酸6（dinor-NOHA），N-（4-氯苯基）-N '-羟基胍（8）和N-羟基胍（7）本身，通过NOS II或（6 R）-5，6，7，8-四氢-1-生物蝶呤（BH 4）-游离NOS II，以比较的方式进行了研究。重组无BH 4 NOS II催化NADPH和O2氧化所有N-羟基胍，形成NO2-和NO3-的速率在20和80 nmol min-1（mg蛋白质）-1之间。在化合物8的情况下，除了NO2-和NO3-的形成之外，还检测到相应的尿素和氰胺的形成。这些BH 4-自由NOS II依赖性反应被NOS中的电子转移调节剂如硫代瓜氨酸（TC）或咪唑（ImH）抑制，但不被Arg抑制，并且被超氧化物歧化酶（SOD）完全抑制。他们表现出的特征非常相似，以前报道的微粒体细胞色素P450催化氧化N-羟基胍。P450和BH 4-free NOS II反应似乎主要是由来自这些血红素蛋白的氧化酶功能的O2·-进行的。在增加浓度的BH 4的存在下，这些非选择性氧化逐渐消失，而更有选择性的单氧化作用仅发生在N-羟基胍上，它们被NOS II、NOHA、homo-NOHA和8很好地识别。这些单氧合反应具有更强的化学选择性（8被选择性地转化为相应的尿素和NO），并且被Arg抑制，但不被SOD抑制，正如NOS FeII− O2物种所进行的反应所预期的那样。总之，这些结果提供了一个更清楚的说明BH 4在调节NOS的单加氧酶/氧化酶的比例的关键作用。他们还建议一个可能的含义NOS在氧化代谢的某些类别的外源性物质，如N-羟基胍，不仅通过他们的单加氧酶功能，但也通过他们的氧化酶功能。
Oxidations ofl-arginine2, homo-l-arginine1, theirNω-hydroxy derivatives4and3(NOHA and homo-NOHA, respectively), and fourN-hydroxyguanidines,Nω-hydroxynor-l-arginine5(nor-NOHA),Nω-hydroxydinor-l-arginine6(dinor-NOHA),N-(4-chlorophenyl)-N‘-hydroxyguanidine (8), andN-hydroxyguanidine (7) itself, by either NOS II or (6R)-5,6,7,8-tetrahydro-l-biopterin (BH4)-free NOS II, have been studied in a comparative manner. Recombinant BH4-free NOS II catalyzes the oxidation of allN-hydroxyguanidines by NADPH and O2, with formation of NO2-and NO3-at rates between 20 and 80 nmol min-1(mg of protein)-1. In the case of compound8, formation of the corresponding urea and cyanamide was also detected besides that of NO2-and NO3-. These BH4-free NOS II-dependent reactions are inhibited by modulators of electron transfer in NOS such as thiocitrulline (TC) or imidazole (ImH), but not by Arg, and are completely suppressed by superoxide dismutase (SOD). They exhibit characteristics very similar to those previously reported for microsomal cytochrome P450-catalyzed oxidation ofN-hydroxyguanidines. Both P450 and BH4-free NOS II reactions appear to be mainly performed by O2•-derived from the oxidase function of those heme proteins. In the presence of increasing concentrations of BH4, these nonselective oxidations progressively disappear while a much more selective monooxygenation takes place only with theN-hydroxyguanidines that are recognized well by NOS II, NOHA, homo-NOHA, and8. These monooxygenations are much more chemoselective (8being selectively transformed into the corresponding urea and NO) and are inhibited by Arg but not by SOD, as expected for reactions performed by the NOS FeII−O2species. Altogether, these results provide a further clear illustration of the key role of BH4in regulating the monooxygenase/oxidase ratio in NOS. They also suggest a possible implication of NOSs in the oxidative metabolism of certain classes of xenobiotics such asN-hydroxyguanidines, not only via their monooxygenase function but also via their oxidase function.