The heme environment in barley hemoglobin
The heme environment in barley hemoglobin
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DOI：
10.1074/jbc.274.7.4207
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发表时间：
1999-02-12
影响因子：
4.8
通讯作者：
Wittenberg, JB
中科院分区：
文献类型：
--
作者：
Das, TK;Lee, HC;Wittenberg, JB
为了阐明大麦血红蛋白（Hb）中血红素的环境和配体结构，本文用共振拉曼和电子顺磁共振光谱研究了Hb中血红素的配体结构。血红素具有双咪唑配位，两种组氨酸均不具有咪唑特征。大麦血红蛋白具有独特的血红素环境，这是从CO复合物中的Fe-CO和C-O伸缩频率判断的。在534和493 cm（-1）处观察到两个Fe-CO伸缩模，其相对强度对pH敏感。534 cm（-1）构象显示氘位移，表明铁结合的CO可能与远端组氨酸形成氢键。1924 cm（-1）处的C-O伸缩模式被认为与534 cm（-1）构象相关。高的Fe-CO伸缩频率和低的C-O伸缩频率（534和1924 cm（-1），493 cm（-1）的分子量是由末端组氨酸和CO之间的短氢键引起的。构象异构体产生于血红素口袋的开放构象，并且当远端组氨酸远离CO时，构象异构体在酸性条件下成为优势群体。大麦Hb的CO复合物中的结合配体和远端组氨酸之间的相互作用意味着类似的结构可能发生在氧衍生物中，赋予结合氧高稳定性。与抹香鲸肌红蛋白相比，氧解离速率的急剧下降证实了这种稳定性。
To elucidate the environment and ligand structure of the heme in barley hemoglobin (Hb), resonance Raman and electron paramagnetic resonance spectroscopic studies have been carried out. The heme is shown to have bis-imidazole coordination, and neither of the histidines has imidazolate character. Barley Hb has a unique heme environment as judged from the Fe-CO and C-O stretching frequencies in the CO complex. Two Fe-CO stretching modes are observed with frequencies at 534 and 493 cm(-1), with relative intensities that are pH sensitive. The 534 cm(-1) conformer shows a deuterium shift, indicating that the iron-bound CO is hydrogen-bonded, presumably to the distal histidine, A C-O stretching mode at 1924 cm(-1) is assigned as being associated with the 534 cm(-1) conformer. Evidence is presented that the high Fe-CO and low C-O stretching frequencies (534 and 1924 cm(-1), respectively) arise from a short hydrogen bond between the distal histidine and the CO. The 493 cm(-1) conformer arises from an open conformation of the heme pocket and becomes the dominant population under acidic conditions when the distal histidine moves away from the CO. Strong hydrogen bonding between the bound ligand and the distal histidine in the CO complex of barley Hb implies that a similar structure may occur in the oxy derivative, imparting a high stability to the bound oxygen. This stabilization is confirmed by the dramatic decrease in the oxygen dissociation rate compared with sperm whale myoglobin.