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从A1A和A1B位点到连接的铂纳米颗粒的电子转移需要FeS簇来抑制复合通道。

Electron transfer from the A1A and A1B sites to a tethered Pt nanoparticle requires the FeS clusters for suppression of the recombination channel.

作者信息

Gorka Michael, Perez Adam, Baker Carol S, Ferlez Bryan, van der Est Art, Bryant Donald A, Golbeck John H

机构信息

Department of Chemistry, The Pennsylvania State University, University Park, PA 16802, United States.

Department of Biochemistry and Molecular Biology, The Pennsylvania State University, University Park, PA 16802, United States.

出版信息

J Photochem Photobiol B. 2015 Nov;152(Pt B):325-34. doi: 10.1016/j.jphotobiol.2015.08.015. Epub 2015 Aug 15.

Abstract

In this work, a previously described model of electron withdrawal from the A1A/A1B sites of Photosystem I (PS I) was tested using a dihydrogen-producing PS I-NQ(CH2)15S-Pt nanoconstruct. According to this model, the rate of electron transfer from A1A/A1B to a tethered Pt nanoparticle is kinetically unfavorable relative to the rate of forward electron transfer to the FeS clusters. Dihydrogen is produced only when an external donor rapidly reduces P700(+), thereby suppressing the recombination channel and allowing the electron in the FeS clusters to proceed via uphill electron transfer through the A1A/A1B quinones to the Pt nanoparticle. We tested this model by sequentially removing the FeS clusters, FB, FA, and FX, and determining the concentration of cytochrome c6 (Cyt c6) at which the backreaction was outcompeted and dihydrogen production was observed. P700-FA cores were generated in a menB insertionally inactivated strain by removing FB with HgCl2; P700-FX cores were generated in a menB psaC insertionally inactivated strain that lacks FA and FB, and P700-A1 cores were generated in a menB rubA insertionally inactivated strain that lacks FX, FA and FB. Quinone incorporation was measured using transient electron paramagnetic resonance spectroscopy and time resolved optical spectroscopy. Cyt c6 was titrated into each of these PS I preparations and the kinetics of P700(+) reduction were measured. A similar experiment was carried out on PS I-NQ(CH2)15S-Pt nanoconstructs assembled from these PS I preparations. This study showed that the concentration of Cyt c6 needed to produce dihydrogen was comparable to that needed to suppress the backreaction. We conclude that the FeS clusters serve to 'park' the electron and thereby extend the duration of the charge-separated state; however, in doing so, the redox advantage of removing the electron at A1A/A1B is lost.

摘要

在这项工作中,使用产氢的光系统I(PS I)-NQ(CH2)15S-Pt纳米构建体测试了先前描述的从光系统I(PS I)的A1A/A1B位点夺取电子的模型。根据该模型,相对于向前电子转移至FeS簇的速率,从A1A/A1B向连接的Pt纳米颗粒的电子转移速率在动力学上是不利的。仅当外部供体迅速还原P700(+)时才产生氢气,从而抑制复合通道,并使FeS簇中的电子通过A1A/A1B醌进行上坡电子转移至Pt纳米颗粒。我们通过依次去除FeS簇、FB、FA和FX,并确定在其中逆反应被竞争且观察到氢气产生的细胞色素c6(Cyt c6)的浓度来测试该模型。通过用HgCl2去除FB,在menB插入失活菌株中产生P700-FA核心;在缺乏FA和FB的menB psaC插入失活菌株中产生P700-FX核心,并且在缺乏FX、FA和FB的menB rubA插入失活菌株中产生P700-A1核心。使用瞬态电子顺磁共振光谱和时间分辨光谱测量醌的掺入。将Cyt c6滴定到这些PS I制剂中的每一种中,并测量P700(+)还原的动力学。对由这些PS I制剂组装的PS I-NQ(CH2)15S-Pt纳米构建体进行了类似的实验。这项研究表明,产生氢气所需的Cyt c6浓度与抑制逆反应所需的浓度相当。我们得出结论,FeS簇用于“停放”电子,从而延长电荷分离态的持续时间;然而,这样做会失去在A1A/A1B处去除电子的氧化还原优势。

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