Department of Biological Sciences, Biochemistry and Molecular Biology Section, Louisiana State University, Baton Rouge, Louisiana 70803, USA.
Biochemistry. 2010 Jan 12;49(1):36-41. doi: 10.1021/bi9017818.
The Photosystem II extrinsic proteins PsbO, PsbP, and PsbQ are required for efficient oxygen-evolving activity under physiological conditions. In this study, we have used fluorescence decay kinetics to quantitatively probe Photosystem II electron transport upon depletion of these components by standard salt washing protocols. Our results indicate that in addition to the expected oxidizing-side defects, removal of PsbP and PsbQ with 2 M NaCl significantly slows the rate of electron transfer from Q(A)(-) to Q(B). Electron transfer from Q(A)(-) to Q(B) in Photosystem II reaction centers with an occupied Q(B) site was slowed by a factor of 12, while electron transport from Q(A)(-) to Q(B) in centers with an unoccupied Q(B) site was slowed by a factor of 6. Subsequent removal of the PsbO protein by treatment with 200 mM NaCl and 2.6 M urea did not induce further reducing-side alterations. Our results demonstrate that studies attributing defects observed upon PsbP and PsbQ removal solely to the oxidizing side must be viewed with caution.
在生理条件下，光系统 II 外在蛋白 PsbO、PsbP 和 PsbQ 对于有效的氧释放活性是必需的。在这项研究中，我们使用荧光衰减动力学来定量探测在这些组件被标准盐洗方案耗尽时的光系统 II 电子传递。我们的结果表明，除了预期的氧化侧缺陷之外，用 2 M NaCl 去除 PsbP 和 PsbQ 还显著降低了从 Q(A)(-)到 Q(B)的电子转移速率。占据 Q(B)位点的光系统 II 反应中心中，Q(A)(-)到 Q(B)的电子转移速度减缓了 12 倍，而未占据 Q(B)位点的中心中，Q(A)(-)到 Q(B)的电子转移速度减缓了 6 倍。随后用 200 mM NaCl 和 2.6 M 脲处理去除 PsbO 蛋白，没有诱导进一步的还原侧改变。我们的结果表明，对于仅归因于氧化侧的 PsbP 和 PsbQ 去除观察到的缺陷的研究必须谨慎对待。
