Lovyagina E R, Luneva O G, Loktyushkin A V, Semin B K
Department of Biophysics, Faculty of Biology, Lomonosov Moscow State University, Moscow 119234, Russia.
Department of Biophysics, Faculty of Biology, Lomonosov Moscow State University, Moscow 119234, Russia.
J Inorg Biochem. 2023 Jul;244:112237. doi: 10.1016/j.jinorgbio.2023.112237. Epub 2023 Apr 23.
Lanthanide cations (La and Tb) bind to the Ca-binding site of the oxygen-evolving complex in Ca-depleted PSII membranes and irreversibly inhibit the oxygen evolution. Оn the other hand, EPR measurement of Mn concentration in buffer revealed that lanthanide cations inhibit the light-dependent oxidation of Mn cations via the high-affinity Mn-binding site in Mn-depleted PSII membranes, which suggests that they bind to and inhibit the high-affinity Mn-binding site of the oxygen-evolving complex. The inhibition is irreversible, bound Ln cation could not be washed out from the sample. Calcium ion inhibits oxidation of Mn (5 μM) at very high concentration (tens mM) and the inhibition is reversible. In this work we measured the reduction rate of exogenic electron acceptor 2,6-dichlorophenolindophenol during the oxidation of Mn cations in the Ca-depleted PSII and in the Ca-depleted PSII treated with lanthanides after extraction of Mn cluster from these preparations. We found that irreversible binding of the lanthanide cation to the Ca-binding site in the Ca-depleted PSII membranes leads to a partial inhibition of the high-affinity Mn-binding site.
镧系阳离子（La和Tb）与缺钙的光系统II（PSII）膜中放氧复合体的钙结合位点结合，并不可逆地抑制氧气释放。另一方面，对缓冲液中锰浓度的电子顺磁共振测量表明，镧系阳离子通过缺锰的PSII膜中的高亲和力锰结合位点抑制锰阳离子的光依赖性氧化，这表明它们与放氧复合体的高亲和力锰结合位点结合并抑制该位点。这种抑制是不可逆的，结合的镧系阳离子无法从样品中洗出。钙离子在非常高的浓度（数十毫摩尔）下抑制锰（5微摩尔）的氧化，且这种抑制是可逆的。在这项工作中，我们测量了在从这些制剂中提取锰簇后，缺钙的PSII以及用镧系元素处理的缺钙PSII中锰阳离子氧化过程中外源电子受体2,6-二氯酚靛酚的还原速率。我们发现，镧系阳离子与缺钙的PSII膜中的钙结合位点的不可逆结合会导致高亲和力锰结合位点受到部分抑制。
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