Yang Jing, Dong Chao, Kirk Martin L
Department of Chemistry and Chemical Biology, The University of New Mexico, MSC03 2060, 1 University of New Mexico, Albuquerque, NM87131-0001, USA.
Dalton Trans. 2017 Oct 10;46(39):13242-13250. doi: 10.1039/c7dt01728f.
A combination of reaction coordinate computations, resonance Raman spectroscopy, spectroscopic computations, and hydrogen bonding investigations have been used to understand the importance of substrate orientation along the xanthine oxidase reaction coordinate. Specifically, 4-thiolumazine and 2,4-dithiolumazine have been used as reducing substrates for xanthine oxidase to form stable enzyme-product charge transfer complexes suitable for spectroscopic study. Laser excitation into the near-infrared molybdenum-to-product charge transfer band produces rR enhancement patterns in the high frequency in-plane stretching region that directly probe the nature of this MLCT transition and provide insight into the effects of electron redistribution along the reaction coordinate between the transition state and the stable enzyme-product intermediate, including the role of the covalent Mo-O-C linkage in facilitating this process. The results clearly show that specific Mo-substrate orientations allow for enhanced electronic coupling and facilitate strong hydrogen bonding interactions with amino acid residues in the substrate binding pocket.
结合反应坐标计算、共振拉曼光谱、光谱计算和氢键研究，以了解沿黄嘌呤氧化酶反应坐标的底物取向的重要性。具体而言，4-硫代鲁马嗪和2,4-二硫代鲁马嗪已被用作黄嘌呤氧化酶的还原底物，以形成适用于光谱研究的稳定酶-产物电荷转移复合物。激光激发进入近红外钼到产物的电荷转移带，在高频面内拉伸区域产生共振拉曼增强模式，直接探测这种金属-配体电荷转移跃迁的性质，并深入了解沿反应坐标在过渡态和稳定的酶-产物中间体之间电子重新分布的影响，包括共价Mo-O-C键在促进这一过程中的作用。结果清楚地表明，特定的钼-底物取向允许增强电子耦合，并促进与底物结合口袋中氨基酸残基的强氢键相互作用。
