The effect of oxalate, malonate, lactate, and succinate chelators on the reduction of Phanerochaete chrysosporium manganese peroxidase compound II by MnII was investigated using stopped-flow techniques. All rate data were collected from single-turnover experiments under pseudo-first-order conditions. With oxalate, the reduction of compound II by MnII exhibited saturation behavior when the observed pseudo-first-order rate constants were plotted against oxalate concentration. The plots passed through the origin, indicating that the reduction by MnII is irreversible at all concentrations of oxalate. Maximal stimulation of the rate of compound II reduction occurred at 2 mM oxalate, the concentration of oxalate found in the extracellular medium of agitated cultures of this fungus. In contrast, maximal stimulation of the reduction of compound II by MnII only was observed at high (> 20 mM) nonphysiological concentrations of malonate and lactate. Furthermore, at low concentrations of malonate and lactate, the reduction of compound II appeared to be reversible. These results suggest that at physiological concentrations oxalate chelates and stabilizes MnIII, enhancing its efficient removal from the enzyme. The rate constants for compound II reduction exhibited bell-shaped curves as a function of pH and had optima at pHs 5.0-5.4. In the presence of succinate, triphasic kinetics were observed for compound II reduction by MnII. In contrast to the reduction of compound II by MnII, various chelators had no observable effect on the formation of compound I. However, they did affect the steady-state oxidation of 2,6-dimethoxyphenol.

中文翻译：

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锰过氧化物酶化合物II还原的机理。有机酸螯合剂和pH值的影响。

使用停止流技术研究了草酸盐，丙二酸盐，乳酸盐和琥珀酸盐螯合剂对MnII还原Phanerochaete chsssporium锰过氧化物酶化合物II的影响。所有费率数据均来自伪一阶条件下的单周转实验。用草酸盐，当将观察到的拟一级反应速率常数对草酸盐浓度作图时，MnII对化合物II的还原表现出饱和行为。该图通过原点，表明在所有草酸盐浓度下，MnII的还原都是不可逆的。在2 mM的草酸盐下最大程度地刺激了化合物II的还原速率，草酸盐是在这种真菌的搅拌培养物的细胞外培养基中发现的草酸盐浓度。相反，仅在高（> 20 mM）的非生理浓度的丙二酸酯和乳酸酯中观察到了仅通过MnII最大程度地刺激化合物II还原。此外，在丙二酸酯和乳酸酯的低浓度下，化合物II的还原似乎是可逆的。这些结果表明，在生理浓度下草酸盐螯合并稳定了MnIII，增强了从酶中的有效去除。化合物II还原的速率常数表现出作为pH的函数的钟形曲线，并且在pH 5.0-5.4下具有最佳值。在琥珀酸酯的存在下，观察到通过MnII还原化合物II的三相动力学。与通过MnII还原化合物II相比，各种螯合剂对化合物I的形成没有明显影响。但是，它们确实影响了2,6-二甲氧基苯酚的稳态氧化。