Unusual spectroscopic and electrochemical properties of the 2[4Fe-4S] ferredoxin of Thauera aromatica
Unusual spectroscopic and electrochemical properties of the 2[4Fe-4S] ferredoxin of Thauera aromatica
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DOI：
10.1021/bi9927890
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发表时间：
2000-04-25
期刊：
影响因子：
2.9
通讯作者：
Lowe, DJ
中科院分区：
文献类型：
--
作者：
Boll, M;Fuchs, G;Lowe, DJ
还原型铁氧还蛋白是芳香塔氏藻（Thauera aromatica）厌氧芳香代谢关键酶的天然电子供体。它含有两个[4Fe-4S]簇，属于Chromatium vinosum型铁氧还蛋白（CvFd），其与“梭菌”型的不同之处在于两个连续半胱氨酸之间的六个氨基酸插入和C-末端α-螺旋氨基酸延伸。研究了T.芳香族铁氧还蛋白的循环伏安法和多频电子顺磁共振研究。从循环伏安法获得的结果揭示了相对于SHE在-431和-587 mV处存在两个氧化还原转变。当只有一个团簇被还原时（大于-500mV），X带EPR谱表明一个还原的[4Fe-4S]团簇存在S = 3/2和5/2自旋态的混合态，没有观察到典型的S = 1/2 EPR信号。在较低的电位（小于-500 mV），更负的[4Fe-4S]簇显示Q-，X-和S-带EPR谱在20 K，这是典型的一个单一的S = 1/2低自旋[4Fe-4S]簇的g（av）为1.94。然而，当温度逐步降低到4 K时，两个团簇之间的磁相互作用逐渐变得可观察到的S = 1/2和S = 5/2 EPR信号的温度依赖性分裂。在两个团簇都被还原的电势下，观察到额外的低场EPR信号，其只能被分配给自旋>5/2的自旋态。所获得的结果确立了CvFd型铁氧还蛋白的共同的典型氨基酸序列特征决定了[4Fe-4S]簇的不寻常的电化学性质。对T.芳香族铁氧还蛋白是CvFd型铁氧还蛋白中的新的。
A reduced ferredoxin serves as the natural electron donor for key enzymes of the anaerobic aromatic metabolism in the denitrifying bacterium Thauera aromatica. It contains two [4Fe-4S] clusters and belongs to the Chromatium vinosum type of ferredoxins (CvFd) which differ from the "clostridial" type by a six-amino acid insertion between two successive cysteines and a C-terminal alpha-helical amino acid extension. The electrochemical and electron paramagnetic resonance (EPR) spectroscopic properties of both [4Fe-4S] clusters from T. aromatica ferredoxin have been investigated using cyclic voltammetry and multifrequency EPR. Results obtained from cyclic voltammetry revealed the presence of two redox transitions at -431 and -587 mV versus SHE. X-band EPR spectra recorded at potentials when only one cluster was reduced (greater than -500 mV) indicated the presence of a spin mixture of S = 3/2 and 5/2 spin states of one reduced [4Fe-4S] cluster, No typical S = 1/2 EPR signals were observed. At lower potentials (less than - 500 mV), the more negative [4Fe-4S] cluster displayed Q-, X-, and S-band EPR spectra at 20 K which were typical of a single S = 1/2 low-spin [4Fe-4S] cluster with a g(av) of 1.94. However, when the temperature was decreased stepwise to 4 K, a magnetic interaction between the two clusters gradually became observable as a temperature-dependent splitting of both the S = 1/2 and S = 5/2 EPR signals. At potentials where both clusters were reduced, additional low-field EPR signals were observed which can only be assigned to spin states with spins of >5/2. The results that were obtained establish that the common typical amino acid sequence features of CvFd-type ferredoxins determine the unusual electrochemical properties of the [4Fe-4S] clusters. The observation of different spin states in T. aromatica ferredoxin is novel among CvFd-type ferredoxins.