Redox Cycling, pH Dependence, and Ligand Effects of Mn(III) in Oxalate Decarboxylase from Bacillus subtilis.
Redox Cycling, pH Dependence, and Ligand Effects of Mn(III) in Oxalate Decarboxylase from Bacillus subtilis.
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DOI：
10.1021/acs.biochem.6b00891
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发表时间：
2016-11
期刊：
影响因子：
2.9
通讯作者：
U. Twahir;A. Ozarowski;A. Angerhofer
中科院分区：
文献类型：
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作者：
U. Twahir;A. Ozarowski;A. Angerhofer
这篇文章描述了对枯草芽孢杆菌草酸脱羧酶中锰(III)的电子顺磁共振(EPR)实验，这是一种有趣的酶，催化草酸盐的氧化还原中性解离为甲酸盐和二氧化碳。化学氧化还原循环提供了强有力的证据表明两个Mn中心都可以被氧化，尽管N-末端的Mn(II)似乎具有较低的还原电位，并且在中等氧化条件下很可能是+3氧化态的载体，这与普遍认为它代表活性中心的观点一致。值得注意的是，在琥珀酸缓冲液和醋酸盐缓冲液中，未处理的OxDC中可以观察到Mn(III)，而在柠檬酸缓冲液中不能直接观察到。定量分析表明，在琥珀酸缓冲液存在的低pH条件下，EPR可见的锰有16%处于+3氧化态。甲酸盐、乙酸酯和琥珀酸类的小分子羧酸盐配体影响着Mn(III)的精细结构和超精细结构参数。来自先前报告的结果[朱，W.，等人]。(2016)生物化学55,429-434]因此，在允许酶转化草酸后，可以重新解释为甲酸盐结合的锰(III)的证据。Mn(III)EPR信号的pH依赖性与酶活性的相关性很好，这提供了强有力的证据，表明草酸脱羧酶的催化反应是由在氧气存在下产生的Mn(III)驱动的。
This contribution describes electron paramagnetic resonance (EPR) experiments on Mn(III) in oxalate decarboxylase of Bacillus subtilis, an interesting enzyme that catalyzes the redox-neutral dissociation of oxalate into formate and carbon dioxide. Chemical redox cycling provides strong evidence that both Mn centers can be oxidized, although the N-terminal Mn(II) appears to have the lower reduction potential and is most likely the carrier of the +3 oxidation state under moderate oxidative conditions, in agreement with the general view that it represents the active site. Significantly, Mn(III) was observed in untreated OxDC in succinate and acetate buffers, while it could not be directly observed in citrate buffer. Quantitative analysis showed that up to 16% of the EPR-visible Mn is in the +3 oxidation state at low pH in the presence of succinate buffer. The fine structure and hyperfine structure parameters of Mn(III) are affected by small carboxylate ligands that can enter the active site and have been recorded for formate, acetate, and succinate. The results from a previous report [Zhu, W., et al. (2016) Biochemistry 55, 429-434] could therefore be reinterpreted as evidence of formate-bound Mn(III) after the enzyme is allowed to turn over oxalate. The pH dependence of the Mn(III) EPR signal compares very well with that of enzymatic activity, providing strong evidence that the catalytic reaction of oxalate decarboxylase is driven by Mn(III), which is generated in the presence of dioxygen.