Dipartimento di Chimica Ugo Schiff, Università di Firenze, Via della Lastruccia 3-13, Sesto Fiorentino, Florence, Italy.
J Inorg Biochem. 2011 Oct;105(10):1338-43. doi: 10.1016/j.jinorgbio.2011.07.007. Epub 2011 Jul 28.
Fluoride complexes of heme proteins are characterized by unique spectroscopic properties, that provide a simple and direct means to monitor the interactions of the distal heme pocket environment with the iron-bound ligand. In particular, a strong correlation has been demonstrated between the wavelength of the iron-porphyrin charge transfer band at 600-620nm (CT1) and the strength of H-bonding donation from the distal amino acid side chains to the fluoride ion. In parallel, resonance Raman spectra with excitation within either the CT1 band or the charge transfer band at 450-460nm (CT2) have revealed that the iron-fluoride stretching frequency is directly affected by H-bonding to the fluoride ion. On this basis, globins and peroxidases display distinct spectroscopic features, which are strongly dependent on the capability of their distal residues (i.e. histidine, arginine and tryptophan) to be involved in H-bonding with the ligand. In particular, in peroxidases strong H-bonding corresponds to a low iron-fluoride stretching frequency and to a red-shifted CT1 band. The reverse is observed in myoglobin. Interestingly, a truncated hemoglobin of microbial origin (Thermobifida fusca) investigated in the present work, displays the specific spectroscopic signature of a peroxidase, in agreement with the presence of strong H-bonding residues, i.e., tyrosine and tryptophan, within the distal pocket.
血红素蛋白的氟络合物具有独特的光谱特性，为监测远端血红素口袋环境与铁结合配体的相互作用提供了一种简单直接的方法。特别是，已经证明 600-620nm（CT1）处的铁卟啉电荷转移带的波长与从远端氨基酸侧链到氟离子的氢键供体强度之间存在很强的相关性。同时，在 CT1 带或 450-460nm（CT2）处的电荷转移带内激发的共振拉曼光谱表明，铁-氟伸缩频率直接受到与氟离子氢键的影响。在此基础上，球蛋白和过氧化物酶表现出明显的光谱特征，这些特征强烈依赖于其远端残基（即组氨酸、精氨酸和色氨酸）与配体形成氢键的能力。特别是，在过氧化物酶中，强氢键对应于低的铁-氟伸缩频率和 CT1 带的红移。肌红蛋白则相反。有趣的是，本研究中研究的一种来自微生物的截短血红蛋白显示出过氧化物酶的特定光谱特征，这与在远端口袋中存在强氢键供体残基酪氨酸和色氨酸一致。
