Proton-coupled electron transfer: the mechanistic underpinning for radical transport and catalysis in biology
Proton-coupled electron transfer: the mechanistic underpinning for radical transport and catalysis in biology
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DOI：
10.1098/rstb.2006.1874
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发表时间：
2006-08-29
影响因子：
6.3
通讯作者：
Nocera, Daniel G.
中科院分区：
文献类型：
--
作者：
Reece, Steven Y.;Hodgkiss, Justin M.;Nocera, Daniel G.
酶中的电荷传递和催化作用通常依赖于氨基酸自由基作为中间体。这些自由基的产生和传输与质子耦合电子转移（PCET）同义，其本质上是电子和质子隧道的量子力学效应。对PCET的警告是，质子转移（PT）基本上限于相对于电子转移（ET）的短距离。在生物学中，通过进化酶来控制PT和ET在高度不同的长度尺度上的坐标，这种困境得到了解决。在这样做的过程中，酶赋予精细的热力学和动力学控制自由基运输和自由基为基础的催化在辅因子活性位点。本讨论将提出包含正交ET和PT途径的模型系统，从而允许质子和电子隧穿事件被解开。在这种机制背景下，PCET催化单加氧酶的氧-氧键活化被捕获在仿生卟啉氧化还原平台。讨论的结论与自由基为基础的量子催化的天然生物酶，I类大肠杆菌核糖核苷酸还原酶的案例研究。研究表明，该酶利用共线和正交PCET运输电荷从组装的二铁酪氨酰基自由基辅因子的活性位点超过35 A远通过跨越两个蛋白质亚基的氨基酸自由基跳跃途径。
Charge transport and catalysis in enzymes often rely on amino acid radicals as intermediates. The generation and transport of these radicals are synonymous with proton-coupled electron transfer (PCET), which intrinsically is a quantum mechanical effect as both the electron and proton tunnel. The caveat to PCET is that proton transfer (PT) is fundamentally limited to short distances relative to electron transfer (ET). This predicament is resolved in biology by the evolution of enzymes to control PT and ET coordinates on highly different length scales. In doing so, the enzyme imparts exquisite thermodynamic and kinetic controls over radical transport and radical-based catalysis at cofactor active sites. This discussion will present model systems containing orthogonal ET and PT pathways, thereby allowing the proton and electron tunnelling events to be disentangled. Against this mechanistic backdrop, PCET catalysis of oxygen-oxygen bond activation by mono-oxygenases is captured at biornimetic porphyrin redox platforms. The discussion concludes with the case study of radical-based quantum catalysis in a natural biological enzyme, class I Escherichia coli ribonucleotide reductase. Studies are presented that show the enzyme utilizes both collinear and orthogonal PCET to transport charge from an assembled diiron-tyrosyl radical cofactor to the active site over 35 A away via an amino acid radical-hopping pathway spanning two protein subunits.