The molecular properties of the methaemoglobin of Chironomus plumosus L. in solution.
The molecular properties of the methaemoglobin of Chironomus plumosus L. in solution.
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溶液中摇蚊高铁血红蛋白的分子特性。
DOI：
10.1111/j.1432-1033.1967.tb19510.x
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发表时间：
1967
期刊：
影响因子：
--
通讯作者：
W. Scheler
中科院分区：
文献类型：
--
作者：
J. Behlke;W. Scheler
1
本文用分析型超滤法测定了羽摇蚊高铁血红蛋白在不同pH值下的分子量。在弱酸性条件下（pH 5.2 - 7.0），沉降常数为2.73 ± 0.02 S，扩散常数为7.5 - 8.5 F。分子量计算为32，000 ± 1，500。
2
在该pH范围之外，分子量降低。在碱性溶液（pH 9.2-10.0）中，二聚体分子可逆地分裂成单体亚基，平均分子量为14，600 ± 300。
3
在7.5至9.0和低于5.0的pH范围内，存在二聚体和单体分子的混合物。单体-二聚体平衡是pH依赖性的。该平衡的pH 1/2与通过电化学法估计的主电离常数的pH 1/2（pH 1/2= 8.3）一致。血红素结合的水分子的去质子化诱导摇蚊-高铁血红蛋白-分子的四元结构的变化。
4
根据摩擦比和斯托克斯半径，单体和二聚体MetHb-分子具有不对称形状。假设单体形式（pH > 9.2）的旋转椭圆体（扁长型），轴约为24和12.6 A。二聚体分子的相对高的摩擦比可以通过α-和β-单体在它们的长轴方向上的缔合来解释。
1
By means of an analytical ultracentrifuge the molecular weight of purified methaemoglobin from Chironomus plumosus has been determined at different pH values. Under weak acidic conditions (pH 5.2 to 7.0) the sedimentation constant amounts to 2.73 ± 0.02 S and the diffusion constant varies from 7.5 to 8.5 F. The molecular weight was calculated as 32,000 ± 1,500.
2
Outside of this pH-range the molecular weight decreases. In alkaline solution (pH 9.2–10.0) the dimer molecule splits off reversibly into monomer subunits, with an average molecular weight of 14,600 ± 300.
3
In the pH-range 7.5 to 9.0 and below 5.0 there exists a mixture of dimer and monomer molecules. The monomer-dimer-equilibrium is pH-dependent. pH1/2 of this equilibrium coincides with the pH1/2 of the spectrophotometrically estimated main ionization constant (pH1/2= 8.3). The deprotonation of a haemin-bound water molecule induces a change of the quarternary structure of the Chironomus-methaemoglobin-molecule.
4
According to the frictional ratio and the Stoke-radius the monomer and the dimer MetHb-molecules have an asymmetrical shape. Assuming a rotation ellipsoid (prolate type) for the monomer form (pH > 9.2) the axes are about 24 and 12.6 A. The relatively high frictional ratio of the dimer molecule may be interpreted by an association of the α- and β-monomers in direction of their longer axes.