Thermodynamics of oxidation-reduction reactions in mammalian nitric-oxide synthase Isoforms
Thermodynamics of oxidation-reduction reactions in mammalian nitric-oxide synthase Isoforms
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DOI：
10.1074/jbc.m308936200
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发表时间：
2004-04-30
影响因子：
4.8
通讯作者：
Salerno, JC
中科院分区：
文献类型：
--
作者：
Gao, YT;Smith, SME;Salerno, JC
三种哺乳动物一氧化氮合酶在每个 NO 需要 3 个电子的反应中从精氨酸产生 NO，这些电子通过包含 FAD 和 FMN 辅因子的还原酶结构域从 NADPH 供应到催化中心。异构体具有共同的反应机制和还原当量的要求，但在调节方面有所不同；内皮和神经元亚型由电子传递系统的钙/钙调蛋白调节控制，而诱导型亚型在所有生理 Ca2+ 浓度下结合钙调蛋白，并且始终处于开启状态。所有三种异构体中通过黄素域的电子转移的热力学基本相似。主要的黄素状态是 FMN、FMNH.、FMNH2、FAD、FADH(.) 和 FADH(2)。 FMN/FMNH。在所有三种同工型中，对都具有高电势（类似于 100 mV），并且不太可能具有催化能力；其他三个黄素对形成一个近等电位组，聚集在 - 250 mV 附近。因此，吡啶核苷酸对在-325mV下对黄素的还原在热力学上是适度有利的。在饱和精氨酸存在的情况下，所有三种亚型中的铁/铁血红素对都类似于 - 270 mV。 Ca2+/钙调蛋白对内皮一氧化氮合酶 (eNOS) 或神经元一氧化氮合酶 (nNOS) 中任何一对的电位均没有影响。黄素对的 pH 依赖性表明存在与黄素氧化还原/质子化状态偶联的可电离基团。
The three mammalian nitric-oxide synthases produce NO from arginine in a reaction requiring 3 electrons per NO, which are supplied to the catalytic center from NADPH through reductase domains incorporating FAD and FMN cofactors. The isoforms share a common reaction mechanism and requirements for reducing equivalents but differ in regulation; the endothelial and neuronal isoforms are controlled by calcium/calmodulin modulation of the electron transfer system, while the inducible isoform binds calmodulin at all physiological Ca2+ concentrations and is always on. The thermodynamics of electron transfer through the flavin domains in all three isoforms are basically similar. The major flavin states are FMN, FMNH., FMNH2, FAD, FADH(.), and FADH(2). The FMN/FMNH. couple is high potential ( similar to 100 mV) in all three isoforms and is unlikely to be catalytically competent; the other three flavin couples form a nearly isopotential group clustered around - 250 mV. Reduction of the flavins by the pyridine nucleotide couple at - 325 mV is thus moderately thermodynamically favorable. The ferri/ferroheme couple in all three isoforms is similar to - 270 mV in the presence of saturating arginine. Ca2+/calmodulin has no effect on the potentials of any of the couples in endothelial nitric-oxide synthase ( eNOS) or neuronal nitric-oxide synthase ( nNOS). The pH dependence of the flavin couples suggests the presence of ionizable groups coupled to the flavin redox/ protonation states.