Synthetic models of the inactive copper(II)-tyrosinate and active copper(II)-tyrosyl radical forms of galactose and glyoxal oxidases
Synthetic models of the inactive copper(II)-tyrosinate and active copper(II)-tyrosyl radical forms of galactose and glyoxal oxidases
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DOI：
10.1021/ja9700663
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发表时间：
1997-09-03
影响因子：
15
通讯作者：
Tolman, WB
中科院分区：
文献类型：
--
作者：
Halfen, JA;Jazdzewski, BA;Tolman, WB
合成了一系列在1，4，7-三氮杂环己烷骨架上附加了一个或两个取代酚酸盐的新配体的铜-Ⅱ和锌-Ⅱ配合物，并用光吸收、电子顺磁共振、核磁共振和/或共振拉曼光谱、循环伏安以及8种情况下的X-射线结晶学进行了表征。用这些络合物模拟了半乳糖和乙二醛氧化酶(GAO和GLO)的铜-II-酪氨酸型活性中心几何构型的特征，包括氧化还原活性的酚类和外源配体(Cl-、CH3CO2-或CH3CN)在正方形金字塔金属离子的顺赤道位置上的结合。通过对具有不同邻位取代基(包括硫醚基)的酚类配体组成的一系列类似络合物的光吸收和电化学性质的考察，探讨了蛋白质中半胱氨酸(C228)和赤道酪氨酸(Y272)之间唯一的邻位S-C共价键的作用。O-烷基硫基单元对邻位-铜-ⅡLMCT转变和M-II-酚基/M-II-苯氧基自由基氧化还原电位的影响相对较小。在酚类化合物上含有叔丁基保护基团的铜-II和Z(II)络合物的电化学和化学单电子氧化产生了新的物种，它们被鉴定为新的M-II-苯氧基自由基化合物，类似于活性的铜-II-酪氨酸自由基形式的GAO和GLO。对M-II-苯氧基自由基物种进行了光吸收、电子顺磁共振和共振拉曼光谱表征，以及它们的生成和化学还原的化学计量比。与蛋白质类似的铜-II-苯氧基化合物的显著特征包括：EPR沉默表明铜-II离子与结合自由基之间的磁性耦合，UV-Vis光谱中苯氧基自由基的波长(Max)约为410 nm(epsilon x 3900M-1 cm(-1))，以及拉曼光谱中可归因于苯氧基C-O振动(nu(7a))的特征。锌-II类似物的拉曼光谱和电化学行为，以及X-波段EPR谱中g=2.00的各向同性信号，进一步证实了M-II-苯氧基自由基物种的公式。
A series of Cu-II and Zn-II complexes with new ligands having either one or two substituted phenolates appended to the 1,4,7-triazacyclononane frame were prepared and characterized by optical absorption, EPR, NMR, and/or resonance Raman spectroscopy, cyclic voltammetry, and, in eight cases, X-ray crystallography. Features of the active site geometries of the Cu-II-tyrosinate forms of galactose and glyoxal oxidases (GAO and GLO) were modeled by these complexes, including the binding of a redox-active phenolate and an exogenous ligand (Cl-, CH3CO2-, or CH3CN) in a cis-equatorial position of a square pyramidal metal ion. The role of the unique ortho S-C covalent bond between a cysteine (C228) and the equatorial tyrosinate (Y272) in the proteins was probed through an examination of the optical absorption and electrochemical properties of sets of similar complexes comprised of phenolate ligands with differing ortho substituents, including thioether groups. The o-alkylthio unit influences the PhO- --> Cu-II LMCT transition and the M-II-phenolate/M-II-phenoxyl radical redox potential, but to a relatively small degree. Electrochemical and chemical one-electron oxidations of the Cu-II and Z(II) complexes of ligands having tert-butyl protecting groups on the phenolates yielded new species that were identified as novel M-II-phenoxyl radical compounds analogous to the active Cu-II-tyrosyl radical forms of GAO and GLO. The M-II-phenoxyl radical species were characterized by optical absorption, EPR, and resonance Raman spectroscopy, as well as by their stoichiometry of formation and chemical reduction. Notable features of the Cu-II-phenoxyl radical compounds that are similar to their protein counterparts include EPR silence indicative of magnetic coupling between the Cu-II ion and the bound radical, a band with lambda(max) approximate to 410 nm (epsilon x 3900 M-1 cm(-1)) in UV-vis spectra diagnostic for the phenoxyl radical, and a feature attributable to the phenoxyl radical C-O vibration (nu(7a)) in resonance Raman spectra. Similar Raman spectra and electrochemical behavior for the Zn-II analogs, as well as an isotropic signal at g = 2.00 in their X-band EPR spectra, further corroborate the formulations of the M-II-phenoxyl radical species.