ELECTRON-PARAMAGNETIC-RESONANCE AND DIFFERENCE ULTRAVIOLET STUDIES OF MN2+ BINDING TO SERUM TRANSFERRIN
ELECTRON-PARAMAGNETIC-RESONANCE AND DIFFERENCE ULTRAVIOLET STUDIES OF MN2+ BINDING TO SERUM TRANSFERRIN
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DOI：
10.1016/0162-0134(94)85119-0
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发表时间：
1994-04-01
影响因子：
3.9
通讯作者：
CHEN, Y
中科院分区：
文献类型：
--
作者：
HARRIS, WR;CHEN, Y
血清转铁蛋白是哺乳动物蛋白质，其正常功能是通过血液在吸收、储存和利用位点之间运输铁离子。它有两个特定的金属结合位点，除了铁离子外，还能结合多种金属离子。在0.1 M N-（2-羟乙基）哌嗪-N '-2-乙烷酸（Hepes）中，通过电子顺磁共振光谱法（EPR）测定第一当量Mn 2+与脱铁转铁蛋白结合的宏观平衡常数为logK（M1）= 4.06 +/-0.13，pH 7.4。Mn ~（2+）与脱铁转铁蛋白非特异性结合的平衡常数log K_（ns）= 2.93 +/- 0.13。Mn 2+的脱铁转铁蛋白和C-和N-末端非铁转铁蛋白的结合也进行了研究，通过差分紫外光谱。形成Mn（2）Tf的第二步宏观平衡常数为logK（M2）= 2.96 +/- 0.13。Mn 2+结合的位点特异性微常数为N-末端位点的logk（N）= 3.13 +/- 0.09，C-末端位点的logk（C）= 3.80 +/- 0.09。似乎没有任何显着的协同性之间的两个网站就金属结合。已经开发了血清中Mn 2+形态的平衡模型，该模型估计几乎90%的Mn 2+与血清蛋白结合，但仅约1%与转铁蛋白结合。Mn 2+与脱铁转铁蛋白的弱结合以及转铁蛋白明显不能与白蛋白竞争表明Mn-转铁蛋白作为体内主要血清种类的出现必须涉及金属的氧化以形成稳定得多的Mn 3 +-转铁蛋白复合物。计算机模型证实，白蛋白具有足够的结合亲和力，以配合血清中的大部分Mn（II），与血清中常见的低分子量配体竞争。然而，没有足够的数据排除其他蛋白质（如α 2-巨球蛋白）可能与白蛋白竞争Mn（II）的可能性。
Serum transferrin is the mammalian protein whose normal function is to transport ferric ions through the blood among sites of absorption, storage, and utilization. It has two specific metal-binding sites that bind a variety of metal ions in addition to ferric ion. The macroscopic equilibrium constant for the binding of the first equivalent of Mn2+ to apotransferrin has been determined by electron paramagnetic resonance spectroscopy (EPR) to be logK(M1) = 4.06 +/- 0.13 at pH 7.4 in 0.1 M N-(2-hydroxyethyl)piperazine-N'-2-ethane acid (Hepes). An equilibrium constant for nonspecific binding of Mn2+ to apotransferrin of log K-ns = 2.93 +/- 0.13 has also been obtained by using EPR. Binding of Mn2+ to apotransferrin and to both C- and N-terminal nonferric transferrin has also been studied by difference UV spectroscopy. The second stepwise macroscopic equilibrium constant for the formation of Mn(2)Tf is logK(M2) = 2.96 +/- 0.13. The site-specific microconstants for Mn2+ binding are logk(N) = 3.13 +/- 0.09 for the N-terminal site and logk(C) = 3.80 +/- 0.09 for the C-terminal site. There does not appear to be any significant cooperativity between the two sites with respect to metal binding. An equilibrium model for the speciation of Mn2+ in serum has been developed which estimates that almost 90% of Mn2+ is bound to serum proteins, but only similar to 1% is bound to transferrin. The weak binding of Mn2+ to apotransferrin and the obvious inability of transferrin to compete with albumin indicates that the appearance of Mn-transferrin as a major serum species in vivo must involve oxidation of the metal to form the much more stable Mn3+-transferrin complex. The computer model confirms that albumin has a sufficient binding affinity to complex most of the Mn(II) in serum in competition with the common low molecular weight ligands in Serum. However, there is insufficient data to rule out the possibility that some other protein, such as alpha(2)-macroglobulin, may compete with albumin for Mn(II).