Department of Chemistry and Biochemistry, Montana State University, Bozeman, Montana 59717, United States.
Department of Chemistry, Emory University, Atlanta, Georgia 30030, United States.
J Phys Chem Lett. 2022 Jun 30;13(25):5986-5990. doi: 10.1021/acs.jpclett.2c01467. Epub 2022 Jun 23.
[FeFe] hydrogenases are highly active catalysts for hydrogen conversion. Their active site has two components: a [4Fe-4S] electron relay covalently attached to the H binding site and a diiron cluster ligated by CO, CN, and 2-azapropane-1,3-dithiolate (ADT) ligands. Reduction of the [4Fe-4S] site was proposed to be coupled with protonation of one of its cysteine ligands. Here, we used time-resolved infrared (TRIR) spectroscopy on the [FeFe] hydrogenase from (HydA1) containing a propane-1,3-dithiolate (PDT) ligand instead of the native ADT ligand. The PDT modification does not affect the electron transfer step to [4Fe-4S] but prevents the enzyme from proceeding further through the catalytic cycle. We show that the rate of the first electron transfer step is independent of the pH, supporting a simple electron transfer rather than a proton-coupled event. These results have important implications for our understanding of the catalytic mechanism of [FeFe] hydrogenases and highlight the utility of TRIR.
[FeFe]氢化酶是一种高效的氢气转化催化剂。其活性位点由两个组成部分：一个通过共价键连接到 H 结合位点的[4Fe-4S]电子中继器和一个由 CO、CN 和 2-氮杂丙烷-1,3-二硫醇配体（ADT）配位的二铁簇。[4Fe-4S]位点的还原被认为与其中一个半胱氨酸配体的质子化耦合。在这里，我们使用时间分辨红外（TRIR）光谱法研究了含有丙烷-1,3-二硫醇（PDT）配体而不是天然 ADT 配体的 （HydA1）中的[FeFe]氢化酶。PDT 修饰不会影响到[4Fe-4S]的电子转移步骤，但会阻止酶进一步通过催化循环。我们表明，第一个电子转移步骤的速率与 pH 值无关，支持简单的电子转移而不是质子偶联事件。这些结果对我们理解[FeFe]氢化酶的催化机制具有重要意义，并强调了 TRIR 的实用性。
