Villafranca J J, Ransom S C, Gibbs E J
Curr Top Cell Regul. 1985;26:207-19. doi: 10.1016/b978-0-12-152826-3.50023-1.
The purpose of the EPR and NMR studies presented in this article was to determine the spatial relationship between the n1 and n2 metal ion sites of E. coli glutamine synthetase. Table I presents the distances between these two metal ion sites in various complexes using Mn(II) bound to each site. These studies also employed the transition-state analog, methionine sulfoximine, as an active-site probe as well as various nucleotide complexes. Two primary conclusions result from these data. The Mn(II)-Mn(II) distance changes from approximately 10 to approximately 8 A when nucleotides bind to the enzyme presumably as the result of a protein conformational change. Two Mn(II) ions can bind to the enzyme in the presence of the substitution-inert Co(III)-ATP complex, implying that the metal ion [Co(III)] coordinated to the beta-gamma phosphoryl groups in the complex is displaced from the normal n2 metal ion site. A model showing the probable spatial relationships among components of the active site is shown in Fig. 6. This model comprises our current working hypothesis of the active site of glutamine synthetase. Further studies of distance relationships are presently underway in our laboratory and will be placed in the context of this model and the known kinetic mechanism.
本文中呈现的电子顺磁共振（EPR）和核磁共振（NMR）研究的目的是确定大肠杆菌谷氨酰胺合成酶的n1和n2金属离子位点之间的空间关系。表I给出了在各种复合物中，使用与每个位点结合的Mn(II)时这两个金属离子位点之间的距离。这些研究还采用了过渡态类似物甲硫氨酸亚砜亚胺作为活性位点探针以及各种核苷酸复合物。这些数据得出了两个主要结论。当核苷酸与酶结合时，Mn(II)-Mn(II)距离从大约10 Å变为大约8 Å，推测这是蛋白质构象变化的结果。在取代惰性的Co(III)-ATP复合物存在下，两个Mn(II)离子可以与酶结合，这意味着与复合物中β-γ磷酸基团配位的金属离子[Co(III)]从正常的n2金属离子位点被取代。图6展示了一个显示活性位点各组分之间可能空间关系的模型。这个模型构成了我们目前关于谷氨酰胺合成酶活性位点的工作假设。我们实验室目前正在对距离关系进行进一步研究，并将把这些研究置于这个模型和已知动力学机制的背景下。
