A highly reactive p450 model compound I.
A highly reactive p450 model compound I.
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高反应性P450模型化合物I。
DOI：
10.1021/ja903394s
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发表时间：
2009-07-22
影响因子：
15
通讯作者：
Groves, John T.
中科院分区：
文献类型：
--
作者：
Bell, Seth R.;Groves, John T.
水溶液中细胞色素 P450 模型化合物 I [OFeIV−4-TMPyP]+(1) 的检测和动力学表征显示出非凡的 CH 羟基化反应速率。通过停流分光光度法监测 FeIII−4-TMPyP 与 mCPBA 的氧化反应，发现了中间体 1，它在 402 nm 处显示出弱的蓝移 Soret 谱带，在 673 nm 处有吸光度，是典型的卟啉 π 自由基阳离子。该中间体随后被转化为充分表征的 OFeIV−4-TMPyP。全局分析提供了 1 形成的二阶速率常数 k1= (1.59 ± 0.06) × 107M−1s−1，随后进行一级衰变，k2= 8.8 ± 0.1 s−1.1H，13 C NMR 确定 9-xant Hydrol 是 1 氧化呫吨的主要产物（~90% 产率）。在 47.5%18OH2 中进行的电喷雾电离质谱表明 21%18O 掺入，与氧回弹反应情况一致。氧杂蒽/氧杂蒽-d2显示出适度的动力学同位素效应，kH/kD= 2.1。呫吨羟基化 1 发生，具有非常大的二阶速率常数 k3= (3.6 ± 0.3) × 106M−1s−1。 4-芴甲酸与 4-异丙基-和 4-乙基苯甲酸的类似反应也产生了高的 CH 羟基化速率，与易裂开的 C-H 键能密切相关，表明均裂夺氢过渡态。将观察到的 C−H 键裂解速率常数映射到类似底物的 Brønsted−Evans−Polanyi 关系上，确定 H−OFeIV−4-TMPyP 键解离能为 ∼100 kcal/mol。观察到的高动力学反应性被认为是由高卟啉氧化还原电位和自旋态交叉现象引起的。更一般地，活性位点的微妙电荷调节可能导致细胞色素 P450 化合物 I 的高反应性。
The detection and kinetic characterization of a cytochrome P450 model compound I, [OFeIV−4-TMPyP]+(1), in aqueous solution shows extraordinary reaction rates for C−H hydroxylations. Stopped-flow spectrophotometric monitoring of the oxidation of FeIII−4-TMPyP withmCPBA revealed the intermediate1, which displays a weak, blue-shifted Soret band at 402 nm and an absorbance at 673 nm, typical of a porphyrin π-radical cation. This intermediate was subsequently transformed into the well-characterized OFeIV−4-TMPyP. Global analysis afforded a second-order rate constantk1= (1.59 ± 0.06) × 107M−1s−1for the formation of1followed by a first-order decay withk2= 8.8 ± 0.1 s−1.1H and13C NMR determined 9-xanthydrol to be the major product (∼90% yield) of xanthene oxidation by1. Electrospray ionization mass spectrometry carried out in 47.5%18OH2indicated 21%18O incorporation, consistent with an oxygen-rebound reaction scenario. Xanthene/xanthene-d2revealed a modest kinetic isotope effect,kH/kD= 2.1. Xanthene hydroxylation by1occurred with a very large second-order rate constantk3= (3.6 ± 0.3) × 106M−1s−1. Similar reactions of fluorene-4-carboxylic acid and 4-isopropyl- and 4-ethylbenzoic acid also gave high rates for C−H hydroxylation that correlated well with the scissile C−H bond energy, indicating a homolytic hydrogen abstraction transition state. Mapping the observed rate constants for C−H bond cleavage onto the Brønsted−Evans−Polanyi relationship for similar substrates determined the H−OFeIV−4-TMPyP bond dissociation energy to be ∼100 kcal/mol. The high kinetic reactivity observed for1is suggested to result from a high porphyrin redox potential and spin-state-crossing phenomena. More generally, subtle charge modulation at the active site may result in high reactivity of a cytochrome P450 compound I.
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