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首页> 外文期刊>Biochemistry >Spectroscopic evidence for a conformational transition in horseradish peroxidase at very low pH.
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Spectroscopic evidence for a conformational transition in horseradish peroxidase at very low pH.

机译：在非常低的pH值下辣根过氧化物酶构象转变的光谱证据。

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Resonance Raman (RR), electronic absorption, and circular dichroism (CD) spectroscopies of the ferric, ferrous, and ferrous-CO forms of horseradish peroxidase (HRP-C) at pH 3.1 are reported. The CD spectra in the UV region show only a small decrease in the alpha-helical content upon pH lowering, whereas dramatic changes are observed in the Soret region. The final form of ferric HRP-C is 5-coordinate high-spin heme whose histidine ligand is replaced by a water ligand with a polar character. The electronic and CD spectra show the presence of an intermediate form with a 6-coordinate heme. Therefore, the cleavage of the proximal Fe-imidazole bond is preceded by the binding of a distal water molecule. For the ferrous form of HRP-C, the pH-dependence of the absorption spectra revealed only the native form in the range pH 5-7 and an unfolded form with a Soret maximum at 383 nm at pH 3.1. An intermediate state, characterized by a Soret maximum at 424 nm, was observed only in a transient way, within a few milliseconds. A metastable and a final species are observed also for the ferrous-CO complex at pH 3.1, as proved by isosbestic points in the electronic absorption spectra. The two forms show different RR nu(Fe-C) and IR nu(CO) modes. The metastable form corresponds to a heme where histidine is replaced by water. The final form is due to the displacement of the water ligand by the proximal histidine. We propose a kinetic model to account for our results at pH 3.1 for the ferric, ferrous, and ferrous-CO forms.
机译：报道了在pH 3.1时辣根过氧化物酶（HRP-C）的铁，亚铁和亚铁-CO形式的共振拉曼（RR），电子吸收和圆二色性（CD）光谱。当pH降低时，UV区域的CD光谱仅显示出α-螺旋含量的少量降低，而在Soret区域则观察到了戏剧性的变化。铁HRP-C的最终形式是5配位高自旋血红素，其组氨酸配体被具有极性特征的水配体代替。电子和CD谱显示存在具有6坐标血红素的中间形式。因此，在近端Fe-咪唑键的裂解之前是远端水分子的结合。对于HRP-C的亚铁形式，吸收光谱的pH依赖性显示仅在pH 5-7范围内的天然形式和未折叠形式，Soret最大值在383 nm处pH值为3.1。仅在几毫秒内以瞬态方式观察到一个以424 nm处的Soret最大值为特征的中间状态。如在电子吸收光谱中的等渗点所证明的，在pH 3.1下，亚铁-CO配合物也观察到亚稳态和最终物种。两种形式显示出不同的RR nu（Fe-C）和IR nu（CO）模式。亚稳态形式对应于血红素，其中组氨酸被水取代。最终形式是由于近端组氨酸置换了水配体。我们提出了一个动力学模型来解释我们在pH 3.1下对铁，亚铁和一氧化碳CO形式的结果。

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