Formation of Hexacoordinate Mn(III) in Bacillus subtilis Oxalate Decarboxylase Requires Catalytic Turnover.
Formation of Hexacoordinate Mn(III) in Bacillus subtilis Oxalate Decarboxylase Requires Catalytic Turnover.
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枯草芽孢杆菌草酸脱羧酶中六配位 Mn(III) 的形成需要催化转化。
DOI：
10.1021/acs.biochem.5b01340
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发表时间：
2016
期刊：
影响因子：
2.9
通讯作者：
Richards,NigelGJ
中科院分区：
文献类型：
--
作者：
Zhu,Wen;Wilcoxen,Jarett;Britt,RDavid;Richards,NigelGJ
草酸脱羧酶(OxDC)催化草酸单负离子歧化生成二氧化碳和甲酸盐。长期以来，该酶一直被认为是在周转过程中利用氧气在催化部位形成单核锰(III)或锰(IV)。然而，重组OxDC只含有紧密结合的Mn(II)，在最佳催化条件下(pH 4.2)，直接检测较高氧化态的金属尚未见报道。利用平行模电子顺磁共振光谱，我们现在证明了在OxDC中确实形成了大量的Mn(III)，但只有在酸性条件下草酸盐和氧气存在的情况下才能形成。这些观察结果首次直接支持了Mn(III)从底物上移走一个电子以产生自由基中间体的提议，在这种中间体中，C-C键断裂的势垒显著降低。因此，OxDC是能够稳定和控制强氧化物种Mn(III)的反应活性的少数几种酶之一。
Oxalate decarboxylase (OxDC) catalyzes the disproportionation of oxalic acid monoanion into CO2and formate. The enzyme has long been hypothesized to utilize dioxygen to form mononuclear Mn(III) or Mn(IV) in the catalytic site during turnover. Recombinant OxDC, however, contains only tightly bound Mn(II), and direct spectroscopic detection of the metal in higher oxidation states under optimal catalytic conditions (pH 4.2) has not yet been reported. Using parallel mode electron paramagnetic resonance spectroscopy, we now show that substantial amounts of Mn(III) are indeed formed in OxDC, but only in the presence of oxalate and dioxygen under acidic conditions. These observations provide the first direct support for proposals in which Mn(III) removes an electron from the substrate to yield a radical intermediate in which the barrier to C–C bond cleavage is significantly decreased. Thus, OxDC joins a small list of enzymes capable of stabilizing and controlling the reactivity of the powerful oxidizing species Mn(III).