Diode or tunnel-diode characteristics? Resolving the catalytic consequences of proton coupled electron transfer in a multi-centered oxidoreductase
Diode or tunnel-diode characteristics? Resolving the catalytic consequences of proton coupled electron transfer in a multi-centered oxidoreductase
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DOI：
10.1021/ja054160s
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发表时间：
2005-11-02
影响因子：
15
通讯作者：
Butt, JN
中科院分区：
文献类型：
--
作者：
Gwyer, JD;Richardson, DJ;Butt, JN
蛋白质膜伏安法已被用来定义质子耦合电子转移（PCET）在细胞色素亚硝酸还原酶的多个催化后果。已定义了pH 4至8范围内反映亚硝酸盐限制还原稳态速率的电流-电位曲线。在pH 8下降低电极电位导致催化电流增加，然后在其取与电极电位的任何进一步降低无关的值之前减小。相比之下，在pH 4时，在更正的电极电位下以近似S形的方式引发催化，而在更负的电极电位下催化速率没有明显的衰减。结果表明，活性是通过两个电子和一个质子的耦合转移到酶。在碱性更强的条件下，在较低的电极电位下催化速率的降低表明，只有当还原不与酶的补偿质子化偶联时，才会发生这种速率衰减。酶的减少和/或质子化可能有助于这些活动的定义内的网站进行了讨论。
Protein film voltammetry has been employed to define multiple catalytic consequences of proton coupled electron transfer (PCET) in a cytochromecnitrite reductase. Current−potential profiles reflecting the steady-state rate of nitrite-limited reduction have been defined from pH 4 to 8. Lowering the electrode potential at pH 8 causes the catalytic current to increase and then decrease before it takes a value independent of any further lowering of electrode potential. By comparison, at pH 4, catalysis is initiated at more positive electrode potentials in an approximately sigmoidal fashion with no attenuation of the catalytic rate evident at more negative electrode potentials. The results show that activity is turned on by the coupled transfer of two electrons and one proton to the enzyme. The decreased rate of catalysis at lower electrode potentials under more alkaline conditions shows that this rate attenuation occurs only when reduction is not coupled to compensating protonation(s) of the enzyme. Sites within the enzyme whose reduction and/or protonation may contribute to the definition of these activities are discussed.