Binding of nitric oxide and carbon monoxide to soluble guanylate cyclase as observed with Resonance raman spectroscopy.
Binding of nitric oxide and carbon monoxide to soluble guanylate cyclase as observed with Resonance raman spectroscopy.
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DOI：
10.1021/bi952440m
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发表时间：
1996-02
期刊：
影响因子：
2.9
通讯作者：
G. Deinum;J. R. Stone;Gerald T. Babcock;M. Marletta
中科院分区：
文献类型：
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作者：
G. Deinum;J. R. Stone;Gerald T. Babcock;M. Marletta
已记录可溶性鸟苷酸环化酶 (sGC) 的亚铁血红素的共振拉曼光谱，这是迄今为止已知的唯一受体。NO。根据拉曼光谱高频区域中卟啉核心敏感振动的频率，我们得出结论，当不存在外源配体时，亚铁血红素是五配位的、高自旋的。我们将还原酶中 204 cm-1 处发生的显着振动归因于血红素 Fe(2+)-近端组氨酸伸缩振动。在酶的 .NO 结合形式中，血红素 Fe2+ 保留五配位几何形状。假设 .NO 与血红素的远端结合，该观察结果表明，当 .NO 结合时，弱 Fe-His 键断裂。在 .NO 结合酶中观察到两种同位素敏感振动，一种在 1677 cm-1 处，归因于 N-O 伸缩振动，另一种在 525 cm-1 处，归因于 Fe-NO 伸缩振动。当CO与亚铁血红素结合时，血红素连接是六配位的。由此，我们得出结论，Fe-His 键仍然完整，并且如果 Fe-近端配体键的裂解对于 sGC 的完全激活是必要的，那么 CO 应该只会微弱地激活该酶，事实证明确实如此。在碳一氧酶中，在 472 cm-1 处观察到 Fe-CO 伸缩振动，在 562 cm-1 处检测到 Fe-C-O 弯曲振动。这些频率是迄今为止在血红素蛋白或以咪唑作为近端配体的模型系统中观察到的 Fe-CO 拉伸和 Fe-C-O 弯曲模式中最低的，表明远端口袋中存在显着的负极性。 Fe-His 伸缩振动的负极性和低频可能是 sGC 极低的 O2 亲和力的原因。
Resonance Raman spectra have been recorded for the ferrous heme of soluble guanylate cyclase (sGC), the only receptor known thus far for .NO. On the basis of the frequencies of porphyrin core sensitive vibrations in the high frequency region of the Raman spectrum, we conclude that the ferrous heme is five-coordinate, high spin, when no exogenous ligands are present. We assign a prominent vibration that occurs at 204 cm-1 in the reduced enzyme to the heme Fe(2+)-proximal histidine stretching vibration. In the .NO bound form of the enzyme, the heme Fe2+ retains a five-coordinate geometry. Assuming that .NO binds to the distal side of the heme, this observation indicates that the weak Fe-His bond breaks when .NO binds. Two isotope-sensitive vibrations are observed in the .NO bound enzyme, one at 1677 cm-1, attributed to the N-O stretching vibration, and one at 525 cm-1, attributed to the Fe-NO stretching vibration. When CO is bound to the ferrous heme, the heme ligation is six-coordinate. From this, we conclude that the Fe-His bond is still intact and that, if cleavage of the Fe-proximal ligand bond is necessary for complete activation of sGC, then CO should only weakly activate the enzyme, which has been shown to be the case. In the carbonmonoxy enzyme, the Fe-CO stretching vibration is observed at 472 cm-1 and the Fe-C-O bending vibration is detected at 562 cm-1. These frequencies are the lowest yet observed for the Fe-CO stretching and Fe-C-O bending modes in heme proteins or model systems with imidazole as the proximal ligand and suggest that there is significant negative polarity in the distal pocket. The negative polarity and the low frequency of the Fe-His stretching vibration may account for the very low O2 affinity of sGC.