Howes B D, Fisher K, Lowe D J
School of Molecular Sciences, University of Sussex, Brighton, U.K.
Biochem J. 1994 Jan 15;297 ( Pt 2)(Pt 2):261-4. doi: 10.1042/bj2970261.
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.
肺炎克雷伯氏菌固氮酶的铁钼辅因子（FeMoco）与该酶结合后的质子-电子-核双共振（ENDOR）光谱表明，在游离钼铁蛋白的连二亚硫酸盐还原状态下，包括氮气、乙炔和氰化物在内的多种底物和抑制剂都不会在FeMoco处或其附近结合，这与我们之前的动力学研究结果一致。因此，底物与FeMoco结合的模型必须考虑比Kim和Rees [（1992年）《科学》257, 1677 - 1682]所描述的结构还原程度更高的结构。在酶于2H₂O存在下进行周转后，会有另一组质子可用于交换，即那些在酶周转过程中可产生氢气或生成二氮结合位点的质子；但未观察到此类可交换质子。因此，不能为了解释在FeMoco结构中观察到的“三角铁原子”的异常几何结构而提出这些质子。
