Heterotropic allosterism of monomeric haemoglobins of Chironomus thummi thummi.
Heterotropic allosterism of monomeric haemoglobins of Chironomus thummi thummi.
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摇蚊单体血红蛋白的异向变构。
DOI：
10.1111/j.1432-1033.1972.tb01683.x
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发表时间：
1972
期刊：
影响因子：
--
通讯作者：
G. Buse
中科院分区：
文献类型：
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作者：
K. Gersonde;H. Sick;A. Wollmer;G. Buse
描述了昆虫摇蚊（Chironomus thummi thummi）的两种单体血红蛋白，尽管它们的氧结合曲线是精确的双曲线（希尔系数n= 1.00），但确实表现出玻尔效应（血红蛋白III，25°C时为0.28;血红蛋白IV，25°C时为0.42）。因此，这些血红蛋白可以存在于两种构象状态不同的O2-亲和力。不同状态的ΔS值也不同，低亲和力的酸性构象具有较低的Δ S值，高亲和力的碱性构象具有较高的ΔS值。
在本文中，玻尔效应被认为是从广义的方面，即作为质子结合位点和铁的第6配位点之间的相互作用，因此可以研究以及与氧化血红蛋白。在氧化形式的血红蛋白的情况下，质子结合位点和配位的H2O之间的变构相互作用是我们实验的基础。
在不同波长下测量的血红蛋白氧化形式的吸光度和椭圆率作为pH值的函数，导致滴定曲线的拐点位置不同。根据前面描述的电路过程[21]，计算了根据pH和变构pK值（pKa 2 = 7.30; pKa 1 = 7.00）的组成构象异构体的百分比分布。
在电子自旋共振光谱中，异向性变构通过H2O衍生物的分子内电场对称性的变化来揭示。具有菱形对称性（g 1 ≠g 2）的酸性构象转变为具有轴对称性的碱性构象。酸构象的特征还在于g-1信号中的五条超精细结构线，表明d-电子与z方向上的两个N-核相互作用。超精细结构中缺乏碱性构象表明一个更大的距离的近端咪唑从铁。该距离的pH依赖性变化控制第六配体的亲和力。
考虑到原子模型揭示的相互作用，描述了血红蛋白III的玻尔效应的可能分子机制[8]。
研究表明，摇蚊血红蛋白的玻尔效应机制与脊椎动物血红蛋白的三级结构条件相同[7]。然而，三级结构的这些条件是通过完全不同的一级结构来实现的。
Two monomeric haemoglobins of the insect Chironomus thummi thummi are described which, though their O2-binding curves are exactly hyperbolic (Hill coefficient n= 1.00), do exhibit a Bohr effect (haemoglobin III, 0.28 at 25°C; haemoglobin IV, 0.42 at 25°C). Thus, these haemoglobins can exist in two conformational states differing in O2-affinity. The states are characterized also by different ΔS values; the acid conformation with low affinity possessing a low, the alkaline conformation with high affinity a higher ΔS value.
In this paper the Bohr effect is regarded from generalizing aspects, i.e. as an interaction between the proton-binding site and the 6th coordination point of the iron which can therefore be studied as well with oxidised haemoglobin. In the case of the oxidised form of haemoglobin the allosteric interaction between the proton-binding site and the coordinated H2O was the basis of our experiments.
Absorbance and ellipticity of the oxidised form of haemoglobin measured at different wavelengths as a function of pH result in titration curves differing in the position of their inflection points. On the basis of the circuit process described previously [21], the percentage distribution of the constituent conformation isomers according to pH and the allosteric pK values (pKa2= 7.30; pKa1= 7.00) were calculated.
In electron spin resonance spectroscopy the heterotropic allosterism is revealed by a change in the symmetry of the intramolecular electric field of the H2O-derivative. The acid conformation with rhombic symmetry (g⊥1 ≠g⊥2) is transformed into the alkaline conformation with axial symmetry. The acid conformation is further characterized by five hyperfine structure lines in the g‖1 signal, showing the d-electrons to interact with two N-nuclei in the z-direction. The hyperfine structure lacking in the alkaline conformation indicates a larger distance of the proximal imidazole from the iron. The pH-dependent variation of this distance controlls the affinity of the sixth ligand.
A possible molecular mechanism of the Bohr effect of haemoglobin III is described, considering the interactions, revealed by the atomic model [8].
It is shown that the Bohr effect mechanism in Chironomus haemoglobin is based on the same conditions of tertiary structure as in the case of vertebrate haemoglobins [7]. These conditions of tertiary structure, however, are realized with completely differing primary structures.