Iron oxidation chemistry in ferritin. Increasing Fe/O2 stoichiometry during core formation.
Iron oxidation chemistry in ferritin. Increasing Fe/O2 stoichiometry during core formation.
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DOI：
10.1016/s0021-9258(18)54877-8
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发表时间：
1991-10
期刊：
影响因子：
--
通讯作者：
Bi Xu;N. Chasteen
中科院分区：
文献类型：
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作者：
Bi Xu;N. Chasteen
以前观察到的变化的化学计量的铁氧化过程中的铁在铁蛋白的氧化沉积的起源一直知之甚少。Fe（II）氧化的O2的化学计量的知识是必不可少的，以建立铁的核心形成的机制。在目前的工作中，氧化的Fe（II）的量通过穆斯堡尔谱和质谱消耗的O2测量。通过“pH stat”滴定测量反应中产生的质子数，并通过酶过氧化氢酶对测量的化学计量的影响测量过氧化氢的产生。对于含有低水平铁（24 Fe（II）/蛋白质）的蛋白质样品，发现化学计量为1.95 +/-0.18 Fe（II）/O2，H2 O2为产物，即方程式1。2Fe ~（2+）+O ~（2+）+4 H ~（2+）-2FeOOH + H ~（2+）O ~（2+）+4 H ~（2+）（1）EPR自旋捕获实验表明，没有超氧自由基形成的证据。化学计量随着额外的铁（240-960 Fe/蛋白质）而显著增加，达到如方程式2中的4 Fe（II）/O2的值。4Fe ~（2+）+O ~（2+）+6 H ~（2+）-4FeOOH + 8H ~（2+）随着铁核的逐渐沉积，铁的氧化机制由蛋白质主导的过程（H_2O_2是O ~（2+）还原的主要产物）转变为矿物表面主导的过程（H_2O是主要产物）。这些结果强调了脱铁铁蛋白壳在促进铁氧化的早期阶段的铁沉积之前的多核铁芯的显着发展的重要性。
The origin of previously observed variations in stoichiometry of iron oxidation during the oxidative deposition of iron in ferritin has been poorly understood. Knowledge of the stoichiometry of Fe(II) oxidation by O2 is essential to establishing the mechanism of iron core formation. In the present work, the amount of Fe(II) oxidized was measured by Mössbauer spectrometry and the O2 consumed by mass spectrometry. The number of protons produced in the reaction was measured by “pH stat” titration and hydrogen peroxide production by the effect of the enzyme catalase on the measured stoichiometry. For protein samples containing low levels of iron (24 Fe(II)/protein) the stoichiometry was found to be 1.95 +/- 0.18 Fe(II)/O2 with H2O2 being a product, viz. Equation 1. 2Fe2+ + O2 + 4H2O—-2FeOOH + H2O2 + 4H+ (1) EPR spin trapping experiments showed no evidence of superoxide radical formation. The stoichiometry markedly increased with additional iron (240-960 Fe/protein), to a value of 4 Fe(II)/O2 as in Equation 2. 4Fe2+ + O2 + 6H2O—-4FeOOH + 8H+ (2) As the iron core is progressively laid down, the mechanism of iron oxidation changes from a protein dominated process with H2O2 being the primary product of O2 reduction to a mineral surface dominated process where H2O is the primary product. These results emphasize the importance of the apoferritin shell in facilitating iron oxidation in the early stage of iron deposition prior to significant development of the polynuclear iron core.