Watt G D, Jacobs D, Frankel R B
Department of Chemistry and Biochemistry, University of Colorado, Boulder 80309-0215.
Proc Natl Acad Sci U S A. 1988 Oct;85(20):7457-61. doi: 10.1073/pnas.85.20.7457.
Both mammalian and bacterial ferritin undergo rapid reaction with small-molecule reductants, in the absence of Fe2+ chelators, to form ferritins with reduced (Fe2+) mineral cores. Large, low-potential reductants (flavoproteins and ferredoxins) similarly react anaerobically with both ferritin types to quantitatively produce Fe2+ in the ferritin cores. The oxidation of Fe2+ ferritin by large protein oxidants [cytochrome c and Cu(II) proteins] also occurs readily, yielding reduced heme and Cu(I) proteins and ferritins with Fe3+ in their cores. These latter oxidants also convert enthetically added Fe2+, bound in mammalian or bacterial apo- or holoferritin, to the corresponding Fe3+ state in the core of each ferritin type. Because the protein reductants and oxidants are much larger than the channels leading into the mineral core attached to the ferritin interior, we conclude that redox reactions involving the Fe2+/Fe3+ components of the ferritin core can occur without direct interaction of the redox reagent at the mineral core surface. Our results also suggest that the oxo, hydroxy species of the core, composed essentially of Fe(O)OH, arise exclusively from solvent deprotonation. The long-distance ferritin-protein electron transfer observed in this study may occur by electron tunneling.
在没有亚铁螯合剂的情况下，哺乳动物和细菌铁蛋白都会与小分子还原剂快速反应，形成具有还原态（Fe2+）矿物核心的铁蛋白。大型、低电位还原剂（黄素蛋白和铁氧化还原蛋白）同样会在厌氧条件下与这两种铁蛋白反应，在铁蛋白核心中定量产生Fe2+。大型蛋白质氧化剂[细胞色素c和Cu（II）蛋白]也很容易使Fe2+铁蛋白发生氧化反应，产生还原型血红素和Cu（I）蛋白，以及核心中含有Fe3+的铁蛋白。这些后一种氧化剂还能将结合在哺乳动物或细菌脱铁或全铁蛋白中的外源性添加的Fe2+转化为每种铁蛋白类型核心中的相应Fe3+状态。由于蛋白质还原剂和氧化剂比通向与铁蛋白内部相连的矿物核心的通道大得多，我们得出结论，涉及铁蛋白核心Fe2+/Fe3+成分的氧化还原反应可以在氧化还原试剂不与矿物核心表面直接相互作用的情况下发生。我们的结果还表明，核心的氧代、羟基物种（主要由Fe（O）OH组成）完全源于溶剂去质子化。本研究中观察到的远距离铁蛋白-蛋白质电子转移可能通过电子隧穿发生。
