Protonation of the oxo-bridged heme/copper assemblies: Modeling the oxidized state of the cytochrome c oxidase active site,Journal of Inorganic Biochemistry

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Protonation of the oxo-bridged heme/copper assemblies: Modeling the oxidized state of the cytochrome c oxidase active site
Journal of Inorganic Biochemistry ( IF 3.8 ) Pub Date : 2021-08-27 , DOI: 10.1016/j.jinorgbio.2021.111593
Maria C Carrasco ₁ , Katherine J Dezarn ₁ , Firoz Shah Tuglak Khan ₁ , Shabnam Hematian ₁

Affiliation

In this study on model compounds for the resting oxidized state of the iron‑copper binuclear center in cytochrome c oxidase (CcO), we describe the synthesis of a new μ-oxo-heme/Cu complex, [(TPP)Fe^III–O–Cu^II(tmpa)][B(C₆F₅)₄] (2) {TPP: tetraphenyl porphyrinate(2–); TMPA: tris(2-pyridylmethylamine)}, as well as two protonation events for three μ-oxo-heme/Cu complexes with varying peripheral substituents on the heme site. The addition of increasing amounts of strong acid to these μ-oxo-heme/Cu systems successively led to the generation of the corresponding μ-hydroxo, μ-aquo, and the dissociated complexes. The heme/Cu assemblies bridged through a water ligand are reported here for the first time and the ¹H NMR and ¹⁹F NMR spectral properties are consistent with antiferromagnetically coupled high-spin iron(III) and copper(II) centers. By titration using a series of protonated amines, the pK_a values for the corresponding μ-hydroxo-heme/Cu species (i.e., the first protonation event) have been reported and compared with the pK_a ranges previously estimated for related systems. These synthetic systems may represent structural models for the oxidized Fe^III–X–Cu^II resting state, or turnover intermediates and can be employed to clarify the nature of proton/electron transfer events in CcO.

Synopsis

The resting oxidized state of the cytochrome c oxidase active site contains an Fe_a3−OH_x−Cu_B moiety. Here, we investigated two successive protonation events, for a series of μ-oxo-heme/Cu assemblies and reported the pK_a values for the first protonation event. The μ-aquo-heme/Cu complexes described here are the first examples of such systems.

中文翻译：

氧桥血红素/铜组件的质子化：模拟细胞色素 c 氧化酶活性位点的氧化状态

在这项关于细胞色素c氧化酶 (C c O) 中铁铜双核中心静止氧化状态的模型化合物的研究中，我们描述了一种新的μ-氧代血红素/Cu 复合物 [(TPP)Fe ^III -O-Cu ^II (tmpa)][B(C ₆ F ₅ ) ₄ ] ( 2 ) {TPP: 卟啉四苯酯(2-); TMPA：tris (2-pyridylmethylamine)}，以及三个μ-氧代-血红素/Cu 配合物的两个质子化事件，在血红素位点具有不同的外围取代基。向这些μ添加越来越多的强酸-oxo-heme/Cu 体系相继导致相应的μ -hydroxo、μ -aquo 和解离的复合物的产生。这里首次报道了通过水配体桥接的血红素/Cu 组件，并且¹ H NMR 和¹⁹ F NMR 光谱特性与反铁磁耦合的高自旋铁 (III) 和铜 (II) 中心一致。通过使用一系列质子化胺进行滴定，已报告了相应μ-羟基血红素/Cu 物质（即第一次质子化事件）的 p Ka 值，并与 p K a_进行_了比较先前为相关系统估计的范围。这些合成系统可能代表氧化的 Fe ^III -X-Cu ^II静止状态或转换中间体的结构模型，并可用于阐明 C c O中质子/电子转移事件的性质。