Spectroscopic studies of the effect of ligand donor strength on the Fe-NO bond intradiol dioxygenases.
Spectroscopic studies of the effect of ligand donor strength on the Fe-NO bond intradiol dioxygenases.
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DOI：
10.1021/ic025906f
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发表时间：
2003-01
影响因子：
4.6
通讯作者：
E. Wasinger;Mindy I. Davis;Monita Y. M. Pau;A. Orville;J. Zaleski;B. Hedman;J. Lipscomb;K. Hodgson;E. Solomon
中科院分区：
文献类型：
--
作者：
E. Wasinger;Mindy I. Davis;Monita Y. M. Pau;A. Orville;J. Zaleski;B. Hedman;J. Lipscomb;K. Hodgson;E. Solomon
用X射线吸收光谱（XAS）、紫外-可见吸收光谱（Abs）、磁性圆二色谱（MCD）和变温变场（VTVH）MCD光谱研究了还原型原儿茶酸3，4-双加氧酶及其底物（3，4-二羟基苯甲酸酯，PCA）复合物结合NO的几何结构和电子结构.将结果与先前发表的那些描述为[FeNO]7系统，其中S = 5/2铁中心反铁磁耦合到S = 1 NO-的模型络合物进行比较。XAS边缘前分析表明FeIIIPCD[NO-]和FeIIIPCD[PCA，NO-]中的Fe-NO单元缺乏代表大多数[FeNO]7模型位点的显著增加的边缘前强度。此外，从扩展X射线吸收精细结构（EXAFS）分析，FeIIIPCD[NO-]和FeIIIPCD[PCA，NO-]活性位点显示具有至少1.91 A的Fe-NO距离，比在模型络合物中发现的那些大约0.2 A。减弱的Fe-NO键与键长的整体延长以及VTVH MCD数据显示NO（-）-->FeIII CT跃迁不再沿零场分裂张量的z轴沿着极化的事实一致。较弱的Fe-NO键来自内源性酚盐和底物儿茶酚盐配体的强供体相互作用，这是从CT区域相对于[FeNO]7模型复合物的强度增加以及从XAS边缘位置向较低能量的移位中观察到的。由于NO是O2的类似物，内源性配体供体强度对Fe-NO键的影响对于非血红素铁酶激活O2具有重要意义。
The geometric and electronic structure of NO bound to reduced protocatechuate 3,4-dioxygenase and its substrate (3,4-dihydroxybenzoate, PCA) complex have been examined by X-ray absorption (XAS), UV-vis absorption (Abs), magnetic circular dichroism (MCD), and variable temperature variable field (VTVH) MCD spectroscopies. The results are compared to those previously published on model complexes described as [FeNO]7 systems in which an S = 5/2 ferric center is antiferromagnetically coupled to an S = 1 NO-. XAS pre-edge analysis indicates that the Fe-NO units in FeIIIPCD[NO-] and FeIIIPCD[PCA,NO-] lack the greatly increased pre-edge intensity representative of most [FeNO]7 model sites. Furthermore, from extended X-ray absorption fine structure (EXAFS) analysis, the FeIIIPCD[NO-] and FeIIIPCD[PCA,NO-] active sites are shown to have an Fe-NO distance of at least 1.91 A, approximately 0.2 A greater than those found in the model complexes. The weakened Fe-NO bond is consistent with the overall lengthening of the bond lengths and the fact that VTVH MCD data show that NO(-)-->FeIII CT transitions are no longer polarized along the z-axis of the zero-field splitting tensor. The weaker Fe-NO bond derives from the strong donor interaction of the endogenous phenolate and substrate catecholate ligands, which is observed from the increased intensity in the CT region relative to that of [FeNO]7 model complexes, and from the shift in XAS edge position to lower energy. As NO is an analogue of O2, the effect of endogenous ligand donor strength on the Fe-NO bond has important implications with respect to O2 activation by non-heme iron enzymes.