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首页> 外文期刊>The Journal of Chemical Physics >Magnetic interactions between a [4Fe-4S](1+) cluster and a flavin mononucleotide radical in the enzyme trimethylamine dehydrogenase: A high-field electron paramagnetic resonance study
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Magnetic interactions between a [4Fe-4S](1+) cluster and a flavin mononucleotide radical in the enzyme trimethylamine dehydrogenase: A high-field electron paramagnetic resonance study

机译：三甲胺脱氢酶中[4Fe-4S]（1+）簇与黄素单核苷酸自由基之间的磁相互作用：高场电子顺磁共振研究

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Trimethylamine dehydrogenase is a bacterial enzyme which contains two redox centers: a flavin mononucleotide (FMN) group which constitutes the active site and a [4Fe-4S](1+,2+) cluster which transfers the electrons provided by the FMN to an electron-transferring flavoprotein. According to the x-ray crystal structure, the renter-to-center distance is equal to 12 Angstrom and the nearest atoms of the two centers are separated by a 4 Angstrom gap. Although this arrangement does not appear especially favorable for mediating strong magnetic interactions, a triplet state electron paramagnetic resonance (EPR) spectrum arising from the intercenter magnetic coupling is observed at X band (9 GHz) when the enzyme is reduced by its substrate. In earlier work, the temperature dependence of this spectrum and its analysis based on a tripler state spin Hamiltonian were used to propose the range (0.8-100 cm(-1)) for the parameter J(0) of the isotropic interaction J(0)S(A).S-B, but neither the magnitude of J(0) nor its sign could be further specified [R. C, Stevenson, W. R, Dunham, R. H. Sands, T. P. Singer, and H. Beinert, Biochim. Biophys. Acta 869, 81 (1986)]. In the present work, we have studied the interaction EPR spectrum in the range 9-340 GHz, Numerical simulations based on a spin Hamiltonian describing a system of two S=1/2 interacting spins allowed us to determine the full set of parameters describing the magnetic interactions between the FMN radical and the [4Fe-4S](1+) cluster. In particular, our study demonstrates that the coupling is antiferromagnetic with J(0) = + 0.72 cm(-1). Although this value corresponds to the lower limit of the range proposed previously, it still appears markedly larger than those measured in biological systems in which a similar arrangement of two paramagnetic centers is found. (C) 1998 American Institute of Physics. [S0021-9606(98)01848-0]. [References: 25]
机译：三甲胺脱氢酶是一种细菌酶，包含两个氧化还原中心：黄素单核苷酸（FMN）基团构成活性位点和[4Fe-4S]（1 +，2 +）团簇，将FMN提供的电子转移至电子-转移黄素蛋白。根据X射线晶体结构，磁心到中心的距离等于12埃，并且两个中心的最近原子被4埃间隙隔开。尽管这种布置对于介导强的磁性相互作用似乎不是特别有利，但是当酶被其底物还原时，在X波段（9 GHz）观察到由中心间磁耦合引起的三态电子顺磁共振（EPR）光谱。在较早的工作中，该光谱的温度依赖性及其基于三重态自旋哈密顿量的分析用于为各向同性相互作用J（0）的参数J（0）提出范围（0.8-100 cm（-1））。 ）S（A）.SB，但无法进一步指定J（0）的大小及其符号。 C，史蒂文森，W。R，邓纳姆，R。H. Sands，T。P. Singer和H. Beinert，Biochim。生物物理学。 Act 869，81（1986）]。在当前的工作中，我们研究了9-340 GHz范围内的相互作用EPR谱。基于自旋哈密顿量的描述了两个S = 1/2相互作用自旋的系统的数值模拟使我们能够确定描述自旋哈密顿的完整参数集FMN自由基与[4Fe-4S]（1+）团簇之间的磁性相互作用。特别是，我们的研究表明耦合是反铁磁性的，J（0）= + 0.72 cm（-1）。尽管该值对应于先前提出的范围的下限，但它似乎仍然明显大于在生物系统中测得的值，在生物系统中发现了两个顺磁中心的相似排列。 （C）1998美国物理研究所。 [S0021-9606（98）01848-0]。 [参考：25]

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