Mukai M, Mills C E, Poole R K, Yeh S R
Department of Physiology and Biophysics, Albert Einstein College of Medicine, Bronx, New York 10461, USA.
J Biol Chem. 2001 Mar 9;276(10):7272-7. doi: 10.1074/jbc.M009280200. Epub 2000 Nov 22.
Biochemical studies of flavohemoglobin (Hmp) from Escherichia coli suggest that instead of aerobic oxygen delivery, a dioxygenase converts NO to NO3(-) and anaerobically, an NO reductase converts NO to N(2)O. To investigate the structural features underlying the chemical reactivity of Hmp, we have measured the resonance Raman spectra of the ligand-free ferric and ferrous protein and the CO derivatives of the ferrous protein. At neutral pH, the ferric protein has a five-coordinate high-spin heme, similar to peroxidases. In the ferrous protein, a strong iron-histidine stretching mode is present at 244 cm(-1). This frequency is much higher than that of any other globin discovered to date, although it is comparable to those of peroxidases, suggesting that the proximal histidine has imidazolate character. In the CO derivative, an open and a closed conformation were detected. The distal environment of the closed conformation is very polar, where the heme-bound CO strongly interacts with the B10 Tyr and/or the E7 Gln. These data demonstrate that the active site structure of Hmp is very similar to that of peroxidases and is tailored to perform oxygen chemistry.
对来自大肠杆菌的黄素血红蛋白（Hmp）的生化研究表明，双加氧酶不是进行有氧氧气输送，而是将NO转化为NO3(-)，在厌氧条件下，NO还原酶将NO转化为N2O。为了研究Hmp化学反应性背后的结构特征，我们测量了无配体的铁蛋白和亚铁蛋白以及亚铁蛋白的CO衍生物的共振拉曼光谱。在中性pH值下，铁蛋白具有五配位高自旋血红素，类似于过氧化物酶。在亚铁蛋白中，在244 cm(-1)处存在强烈的铁-组氨酸伸缩模式。尽管该频率与过氧化物酶的频率相当，但远高于迄今为止发现的任何其他球蛋白的频率，这表明近端组氨酸具有咪唑酸酯特征。在CO衍生物中，检测到一种开放构象和一种封闭构象。封闭构象的远端环境非常极性，其中与血红素结合的CO与B10酪氨酸和/或E7谷氨酰胺强烈相互作用。这些数据表明，Hmp的活性位点结构与过氧化物酶非常相似，并且经过调整以进行氧化学作用。
