Russian Journal of Biological Physics and Chemisrty Russian Journal of Biological Physics and Chemisrty АКТУАЛЬНЫЕ ВОПРОСЫ БИОЛОГИЧЕСКОЙ ФИЗИКИ И ХИМИИ 2499-9962 54275 Общая биофизика General biophysics Общая биофизика INHIBITION OF PHOTOSYSTEM II ELECTRON-TRANSPORT CHAIN BY TERBIUM IONS ИНГИБИРОВАНИЕ ЭЛЕКТРОН-ТРАНСПОРТНОЙ ЦЕПИ ФОТОСИСТЕМЫ 2 КАТИОНАМИ ТЕРБИЯ Локтюшкин А В Loktyushkin A V Ловягина Е Р Lovyagina E R Elena.Lovyagina@gmail.com Семин Б К Semin B K Московский государственный университет им. М.В. Ломоносова ru Lomonosov Moscow State University ru Московский государственный университет им. М.В. Ломоносова ru Lomonosov Moscow State University ru Московский государственный университет им. М.В. Ломоносова ru Lomonosov Moscow State University ru 25 06 2018 25 06 2018 3 2 250 254 20 06 2018 20 06 2018 https://rusjbpc.ru/en/nauka/article/54275/view

Светозависимое окисление воды и выделение молекулярного кислорода в оксигенных организмах осуществляется кислород-выделяющим комплексом (КВК) фотосистемы 2 (ФС2). Каталитическим центром КВК является кластер Mn4CaO5, структура которого в настоящее время расшифрована. Присутствие катионов кальция обязательно для функционирования КВК, и их удаление при сохранении катионов марганца в каталитическом центре приводит к ингибированию функции выделения кислорода. Однако механизм участия Ca2+ в функционировании КВК до сих пор не установлен. Известно, что некоторые ионы редкоземельных элементов имеют сходные с ионами кальция физико-химические свойства и взаимодействуют с Ca2+-связывающими белками. Такое связывание либо ингибирует функциональную активность белка, либо может частично восстанавливать её в отсутствие Ca2+. В настоящей работе исследовано влияние одного из редкоземельных элементов (тербия) на скорость электронного транспорта в мембранных препаратах ФС2. Основной акцент сделан на сопоставлении влияния катионов тербия на функцию выделения кислорода и транспорт электронов через ФС2 к искусственному акцептору. Обнаружено, что Tb3+ ингибирует выделение кислорода более эффективно, чем восстановление искусственного акцептора электронов 2,6-дихлорофенолиндофенола на акцепторной стороне ФС2, то есть его действие приводит к разобщению этих процессов. Аналогичный эффект наблюдается при экстракции катионов кальция из КВК [Semin et al. Photosynth. Res. 98 (2008) 235]. Предполагается, что ингибирующий эффект катионов тербия связан с замещением Са2+ и/или вытеснением периферических белков PsbP и PsbQ из ФС2.

Light-dependent water oxidation and evolution of molecular oxygen in the oxygenic organisms is performed by oxygen-evolving complex (OEC) of photosystem II (PSII). Catalytic center of the OEC is the Mn4CaO5 cluster the structure of which is determined now. The presence of calcium cation in the OEC is necessary for OEC function and extraction of this cation from the OEC without depletion of Mn cations inhibits the oxygen evolution reaction. However, the mechanism of Ca2+ participation in the water splitting by OEC is unclear now. It is known that the ions of rare-earth metals have similar physical and chemical properties with Ca2+ ions and interact with Ca2+-binding proteins. Possibly such interaction could either inhibit the protein function in the absence of Ca2+ or could partially reduce it function in the absence of Ca2+. In the present study it was investigated the effect of the one of rare-earth metals - terbium - on the electron-transport rate in the membrane preparations of PSII. The focus of attention in our study was the correlation between the terbium effect on the oxygen evolution reaction and the electron transport to artificial electron acceptor. We found that Tb3+ inhibits the oxygen evolution more effectively then reduction of the artificial electron acceptor 2,6-dichlorophenolindophenol on the acceptor side of PSII that is terbium action provides the decoupling of these processes. Similar effect is observed in Ca-depleted PSII membranes [Semin et al. Photosynth. Res. 98 (2008) 235]. Taking these results into account we suppose that terbium inhibition effect is determined by its substitution of Ca2+ cation in the OEC and/or extraction of extrinsic proteins PsbP and PsbQ.

 фотосистема 2 тербий кальций кислород-выделяющий комплекс photosystem II terbium calcium oxygen-evolving complex

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