Noji Tomoyasu, Saito Keisuke, Ishikita Hiroshi
Department of Applied Chemistry, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-8654, Japan.
Research Center for Advanced Science and Technology, The University of Tokyo, 4-6-1 Komaba, Meguro-ku, Tokyo 153-8904, Japan.
Biochemistry. 2025 Jan 7;64(1):203-212. doi: 10.1021/acs.biochem.4c00521. Epub 2024 Dec 10.
Photosystem I (PSI) from utilizes chlorophyll (Chl) with a formyl group as its primary pigment, which is more red-shifted than chlorophyll (Chl) in PSI from . Using the cryo-electron microscopy structure and solving the linear Poisson-Boltzmann equation, here we report the redox potential () values in PSI. The (Chl) values at the paired chlorophyll site, [PP], are nearly identical to the corresponding (Chl) values in PSI, despite Chl having a 200 mV lower reduction power. The accessory chlorophyll site, A, in the B branch exhibits an extensive H-bond network with its ligand water molecule, contributing to (A) being lower than (A). The substitution of pheophytin (Pheo) with Chl at the electron acceptor site, A, decreases (A), resulting in an uphill electron transfer from A. The impact of the A formyl group on (A) is offset by the reorientation of the A ester group. It seems likely that Pheo is necessary for PSI to maintain the overall electron-transfer cascade characteristic of PSI in its unique light environment.
来自[具体来源]的光系统I（PSI）利用带有甲酰基的叶绿素（Chl）作为其主要色素，该色素的红移程度比来自[另一来源]的PSI中的叶绿素（Chl）更大。利用低温电子显微镜结构并求解线性泊松 - 玻尔兹曼方程，我们在此报告了[具体来源]的PSI中的氧化还原电位（）值。尽管Chl的还原能力低200 mV，但在配对叶绿素位点[PP]处的（Chl）值与[另一来源]的PSI中的相应（Chl）值几乎相同。B分支中的辅助叶绿素位点A与其配体水分子形成广泛的氢键网络，导致（A）低于（A）。在电子受体位点A处用Chl取代脱镁叶绿素（Pheo）会降低（A），导致从A进行向上的电子转移。A甲酰基对（A）的影响被A酯基的重新取向所抵消。似乎脱镁叶绿素对于[具体来源]的PSI在其独特的光环境中维持PSI的整体电子传递级联特性是必要的。
