Bou-Abdallah Fadi, Lewin Allison C, Le Brun Nick E, Moore Geoffrey R, Chasteen N Dennis
Department of Chemistry, University of New Hampshire, Durham, New Hampshire 03824, USA.
J Biol Chem. 2002 Oct 4;277(40):37064-9. doi: 10.1074/jbc.M205712200. Epub 2002 Jul 17.
Bacterioferritin (EcBFR) of Escherichia coli is an iron-mineralizing hemoprotein composed of 24 identical subunits, each containing a dinuclear metal-binding site known as the "ferroxidase center." The chemistry of Fe(II) binding and oxidation and Fe(III) hydrolysis using H(2)O(2) as oxidant was studied by electrode oximetry, pH-stat, UV-visible spectrophotometry, and electron paramagnetic resonance spin trapping experiments. Absorption spectroscopy data demonstrate the oxidation of two Fe(II) per H(2)O(2) at the ferroxidase center, thus avoiding hydroxyl radical production via Fenton chemistry. The oxidation reaction with H(2)O(2) corresponds to Fe(II)(2)-P + H(2)O(2) --> Fe(III)(2)O-P + H(2)O, where Fe(II)(2)-P represents a diferrous ferroxidase center complex of the protein P with net charge Z and Fe(III)(2)O-P a micro-oxo-bridged diferric ferroxidase complex. The mineralization reaction is given by 2Fe(2+) + H(2)O(2) + 2H(2)O --> 2FeOOH((core)) + 4H(+), where two Fe(II) are again oxidized by one H(2)O(2). Hydrogen peroxide is shown to be an intermediate product of dioxygen reduction when O(2) is used as the oxidant in both the ferroxidation and mineralization reactions. Most of the H(2)O(2) produced from O(2) is rapidly consumed in a subsequent ferroxidase reaction with Fe(II) to produce H(2)O. EPR spin trapping experiments show that the presence of EcBFR greatly attenuates the production of hydroxyl radical during Fe(II) oxidation by H(2)O(2), consistent with the ability of the bacterioferritin to facilitate the pairwise oxidation of Fe(II) by H(2)O(2), thus avoiding odd electron reduction products of oxygen and therefore oxidative damage to the protein and cellular components through oxygen radical chemistry.
大肠杆菌的细菌铁蛋白（EcBFR）是一种矿化铁的血红蛋白，由24个相同的亚基组成，每个亚基都含有一个被称为“铁氧化酶中心”的双核金属结合位点。通过电极血氧测定法、pH计、紫外可见分光光度法和电子顺磁共振自旋捕获实验，研究了以H₂O₂为氧化剂时Fe(II)的结合与氧化以及Fe(III)的水解反应。吸收光谱数据表明，在铁氧化酶中心，每分子H₂O₂可氧化两个Fe(II)，从而避免了通过芬顿化学产生羟基自由基。与H₂O₂的氧化反应为Fe(II)₂-P + H₂O₂ → Fe(III)₂O-P + H₂O，其中Fe(II)₂-P代表蛋白质P的二价铁铁氧化酶中心复合物，净电荷为Z，Fe(III)₂O-P为微氧桥连的二价铁铁氧化酶复合物。矿化反应为2Fe²⁺ + H₂O₂ + 2H₂O → 2FeOOH（核心）+ 4H⁺，其中两个Fe(II)同样被一个H₂O₂氧化。在铁氧化和矿化反应中，当O₂用作氧化剂时，过氧化氢被证明是双原子氧还原的中间产物。由O₂产生的大部分H₂O₂在随后与Fe(II)的铁氧化酶反应中迅速消耗，生成H₂O。电子顺磁共振自旋捕获实验表明，EcBFR的存在极大地减弱了H₂O₂氧化Fe(II)过程中羟基自由基的产生，这与细菌铁蛋白促进H₂O₂对Fe(II)进行成对氧化的能力一致，从而避免了氧的单电子还原产物，进而避免了通过氧自由基化学对蛋白质和细胞成分造成氧化损伤。
