Max-Delbrück-Center for Molecular Medicine, D-13125 Berlin-Buch, Germany.
Phys Chem Chem Phys. 2010 May 14;12(18):4827-32. doi: 10.1039/b924245g. Epub 2010 Mar 16.
Catalase and methaemoglobin have very similar haem groups, which are both ferric, yet catalase decomposes hydrogen peroxide to water and oxygen very efficiently, while methaemoglobin does not. Structural studies have attributed this behaviour to their different distal environments. Here we present Fe L(2,3)-edge X-ray absorption spectra of these proteins in physiological solutions, which reveal clear differences in their electronic structures, in that pi back-donation of the Fe atom occurs in catalase, which confers on it a partial ferryl (Fe(4+)) character, while this is not the case in methaemoglobin. The origin of the Fe(4+) character stems from the proximal tyrosine residue. We also find that both systems are in a high spin state. Temperature effects influence the spectra of catalase only weakly, in agreement with previous studies of its chemical activity. We conclude that the high activity of catalase is not only determined by its distal environment but also by its partial ferryl character.
过氧化氢酶和高铁血红蛋白具有非常相似的血红素基团，都是三价铁，但过氧化氢酶能将过氧化氢高效分解为水和氧气，而高铁血红蛋白则不能。结构研究将这种行为归因于它们不同的远端环境。在这里，我们展示了这些蛋白质在生理溶液中的 Fe L(2,3)-边 X 射线吸收光谱，这些光谱显示出它们在电子结构上的明显差异，即过氧化氢酶中的 Fe 原子发生了 pi 反馈，赋予它部分高铁（Fe(4+)）的特性，而高铁血红蛋白则不是这样。Fe(4+)特性的起源来自于近端的酪氨酸残基。我们还发现，这两个系统都处于高自旋状态。温度对过氧化氢酶的光谱影响较弱，这与之前对其化学活性的研究一致。我们得出的结论是，过氧化氢酶的高活性不仅取决于其远端环境，还取决于其部分高铁特性。
