Yamamoto Y, Hirai Y, Suzuki A
Department of Chemistry, University of Tsukuba, Japan.
J Biol Inorg Chem. 2000 Aug;5(4):455-62. doi: 10.1007/s007750050005.
A novel C2-symmetric ring-fluorinated hemin, 13,17-bis(2-carboxyethyl)-2,8,12,18-tetramethyl-3,7-difluoroporphyrin atoiron(III), has been synthesized and was incorporated into sperm whale apomyoglobin to investigate protein-induced rhombic perturbations on the electronic structure of the active site of myoglobin (Mb) using 19F NMR spectroscopy. NMR signals for 19F atoms introduced as substituents on the present heme in ferrous low-spin and high-spin and ferric low-spin complexes have been observed and their shifts sharply reflect not only the electronic nature of the heme iron, but also in-plane asymmetry of the heme electronic structure. The two-fold symmetric electronic structure of the ring-fluorinated hemin is clearly manifested in the 19F and 1H NMR spectra of its dicyano complex. The chemical equivalence of the two fluorine atoms of the heme is removed in the active site of myoglobin and the splitting of the two 19F NMR signals provides a quantitative probe for characterizing the rhombic perturbation of the heme electronic structure induced by the heme-protein interaction. The in-plane asymmetry of heme electronic structures in carbon-monoxy and deoxy Mbs have been analyzed for the first time on the basis of the shift difference between the two 19F NMR signals of the heme and is interpreted in terms of iron-ligand binding and/or the orbital ground state of the heme. A potential utility of 19F NMR, combined with the use of a symmetric fluorinated hemin, in characterizing the heme electronic structure of myoglobin in a variety of iron oxidation, spin, and ligation states, is presented.
一种新型的C2对称环氟化血红素，即13,17-双（2-羧乙基）-2,8,12,18-四甲基-3,7-二氟卟啉合铁（III），已被合成，并被掺入抹香鲸肌红蛋白原中，以利用19F核磁共振光谱研究蛋白质对肌红蛋白（Mb）活性位点电子结构的菱形扰动。已观察到作为取代基引入到当前亚铁低自旋、高自旋和铁低自旋配合物血红素上的19F原子的核磁共振信号，其位移不仅能敏锐地反映血红素铁的电子性质，还能反映血红素电子结构的面内不对称性。环氟化血红素的二重对称电子结构在其二氰基配合物的19F和1H核磁共振光谱中清晰显现。在肌红蛋白的活性位点中，血红素两个氟原子的化学等价性被消除，两个19F核磁共振信号的分裂为表征血红素-蛋白质相互作用引起的血红素电子结构的菱形扰动提供了一种定量探针。首次基于血红素两个19F核磁共振信号之间的位移差异，分析了一氧化碳肌红蛋白和脱氧肌红蛋白中血红素电子结构的面内不对称性，并根据铁-配体结合和/或血红素的轨道基态进行了解释。本文展示了19F核磁共振结合对称氟化血红素在表征各种铁氧化、自旋和配位状态下肌红蛋白血红素电子结构方面的潜在用途。
