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首页> 外文期刊>Biophysical Chemistry: An International Journal Devoted to the Physical Chemistry of Biological Phenomena >Pentacoordinate and hexacoordinate ferric hemes in acid medium: EPR, UV-Vis and CD studies of the giant extracellular hemoglobin of Glossoscolex paulistus.
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Pentacoordinate and hexacoordinate ferric hemes in acid medium: EPR, UV-Vis and CD studies of the giant extracellular hemoglobin of Glossoscolex paulistus.

机译：酸性介质中的五配位和六配位的铁血红素：Glossoscolex paulistus巨大的细胞外血红蛋白的EPR，UV-Vis和CD研究。

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摘要

The equilibrium complexity involving different axially coordinated hemes is peculiar to hemoglobins. The pH dependence of the spontaneous exchange of ligands in the extracellular hemoglobin from Glossoscolex paulistus was studied using UV-Vis, EPR, and CD spectroscopies. This protein has a complex oligomeric assembly with molecular weight of 3.1 MDa that presents an important cooperative effect. A complex coexistence of different species was observed in almost all pH values, except pH 7.0, where just aquomet species is present. Four new species were formed and coexist with the aquomethemoglobin upon acidification: (i) a "pure" low-spin hemichrome (Type II), also called hemichrome B, with an usual spin state (d(xy))(2)(d(xz),d(yz))(3); (ii) a strong g(max) hemichrome (Type I), also showing an usual spin state (d(xy))(2)(d(xz),d(yz))(3); (iii) a hemichrome with unusual spin state (d(xz),d(yz))(4)(d(xy))(1) (Type III); (iv) and a high-spin pentacoordinate species. CD measurements suggest that the mechanism of species formation could be related with an initial process of acid denaturation. However, it is worth mentioning that based on EPR the aquomet species remains even at acidic pH, indicating that the transitions are not complete. The "pure" low-spin hemichrome presents a parallel orientation of the imidazole ring planes but the strong g(max) hemichrome is a HALS (highly anisotropic low-spin) species indicating a reciprocally perpendicular orientation of the imidazole ring planes. The hemichromes and pentacoordinate formation mechanisms are discussed in detail.
机译：涉及不同轴向配位的血红素的平衡复杂性是血红蛋白特有的。使用紫外-可见，EPR和CD光谱学研究了Glossoscolex paulistus细胞外血红蛋白中配体自发交换的pH依赖性。该蛋白具有分子量为3.1 MDa的复杂寡聚组装体，具有重要的协同作用。在几乎所有的pH值中都观察到了不同物种的复杂共存，除了pH 7.0（仅存在aquomet物种）之外。酸化后形成了四个新物种并与水合高铁血红蛋白共存：（i）一种“纯”低自旋半色素（II型），也称为半色素B，具有通常的自旋态（d（xy））（2）（d （xz），d（yz））（3）; （ii）强g（max）半色（I型），还显示出通常的自旋态（d（xy））（2）（d（xz），d（yz））（3）; （iii）具有异常自旋态的半铬（d（xz），d（yz））（4）（d（xy））（1）（类型III）; （iv）和高自旋五角目种。 CD测量表明物种形成的机制可能与酸变性的初始过程有关。但是，值得一提的是，基于EPR，水族化合物甚至在酸性pH值下仍保持不变，这表明过渡过程不完全。 “纯”低自旋半铬呈现咪唑环平面的平行方向，但强g（max）半铬是HALS（高度各向异性的低自旋）物种，表明咪唑环平面相互垂直。详细讨论了半色和五坐标形成机理。

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