Nitrogenase of Klebsiella pneumoniae: electron nuclear double resonance (ENDOR) studies on the substrate reduction site.
Nitrogenase of Klebsiella pneumoniae: electron nuclear double resonance (ENDOR) studies on the substrate reduction site.
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肺炎克雷伯菌的固氮酶：底物还原位点的电子核双共振 (ENDOR) 研究。
作者：
B. Howes;K. Fisher;D. Lowe
与酶结合的肺炎克雷伯菌固氮酶的铁钼辅因子 (FeMoco) 的质子电子核双共振 (ENDOR) 谱表明，多种底物和抑制剂，包括二氮、乙炔和氰化物，在游离 MoFe 蛋白的连二亚硫酸盐还原状态下不会与 FeMoco 结合或结合，这与我们之前的动力学研究一致。因此，底物与 FeMoco 结合的模型必须考虑比 Kim 和 Rees 描述的水平更低的结构 [(1992) Science 257, 1677-1682]。当酶在 2H2O 存在下翻转后，一组额外的质子可能可用于交换，即那些可以在酶翻转过程中产生二氢或产生氢化二氮结合位点的质子；没有观察到这种可交换质子。因此，不能提出它们来解释 FeMoco 结构中观察到的“三角铁原子”的不寻常几何形状。
Proton electron nuclear double resonance (ENDOR) spectra from the iron-molybdenum cofactor (FeMoco) of Klebsiella pneumoniae nitrogenase bound to the enzyme show that a wide variety of substrates and inhibitors, including dinitrogen, acetylene and cyanide, do not bind at or close to FeMoco in the dithionite-reduced state of the free MoFe protein, in agreement with our previous kinetic studies. Therefore models for substrate binding to FeMoco must consider structures at a more reduced level than that described by Kim and Rees [(1992) Science 257, 1677-1682]. After the enzyme has turned over in the presence of 2H2O, an additional set of protons are potentially available for exchange, namely those that can give rise to dihydrogen during enzyme turnover or generate the hydridic dinitrogen binding site; such exchangeable protons were not observed. They cannot therefore be proposed in order to explain the unusual geometry of the 'trigonal iron atoms' observed in the structure of FeMoco.