Wehner Antje, Storf Stefanie, Jahns Peter, Schmid Volkmar H R
Institut für Biochemie der Pflanzen, Heinrich Heine-Universität Düsseldorf, Germany.
J Biol Chem. 2004 Jun 25;279(26):26823-9. doi: 10.1074/jbc.M402399200. Epub 2004 Apr 7.
The conversion of violaxanthin (Vx) to zeaxanthin (Zx) in the de-epoxidation reaction of the xanthophyll cycle plays an important role in the protection of chloroplasts against photooxidative damage. Vx is bound to the antenna proteins of both photosystems. In photosystem II, the formation of Zx is essential for the pH-dependent dissipation of excess light energy as heat. The function of Zx in photosystem I is still unclear. In this work we investigated the de-epoxidation characteristics of light-harvesting complex proteins of photosystem I (LHCI) under in vivo and in vitro conditions. Recombinant LHCI (Lhcal-4) proteins were reconstituted with Vx and lutein, and the convertibility of Vx was studied in an in vitro assay using partially purified Vx de-epoxidase isolated from spinach thylakoids. All four LHCI proteins exhibited unique de-epoxidation characteristics. An almost complete Vx conversion to Zx was observed only in Lhca3, whereas Zx formation in the other LHCI proteins decreased in the order Lhca4 > Lhca1 > Lhca2. Most likely, these differences in Vx de-epoxidation were related to the different accessibility of the respective carotenoid binding sites in the distinct antenna proteins. The results indicate that Vx bound to site V1 and N1 is easily accessible for de-epoxidation, whereas Vx bound to L2 is only partially and/or with the slower kinetics convertible to Zx. The de-epoxidation properties determined for the monomeric recombinant proteins were consistent with those obtained for isolated native LHCI-730 and LHCI-680 in the same in vitro assay and the de-epoxidation state found under in vivo conditions in native LHCIs.
叶黄素循环的脱环氧化反应中，紫黄质（Vx）向玉米黄质（Zx）的转化在保护叶绿体免受光氧化损伤方面起着重要作用。Vx与两个光系统的天线蛋白结合。在光系统II中，Zx的形成对于以热的形式依赖pH值耗散过量光能至关重要。Zx在光系统I中的功能仍不清楚。在这项工作中，我们研究了光系统I（LHCI）捕光复合蛋白在体内和体外条件下的脱环氧化特性。用Vx和叶黄素重构重组LHCI（Lhcal - 4）蛋白，并使用从菠菜类囊体中分离的部分纯化的Vx脱环氧化酶在体外试验中研究Vx的可转化性。所有四种LHCI蛋白都表现出独特的脱环氧化特性。仅在Lhca3中观察到Vx几乎完全转化为Zx，而其他LHCI蛋白中Zx的形成按Lhca4 > Lhca1 > Lhca2的顺序减少。很可能，Vx脱环氧化的这些差异与不同天线蛋白中各个类胡萝卜素结合位点的不同可及性有关。结果表明，与位点V1和N1结合的Vx易于进行脱环氧化，而与L2结合的Vx仅部分地和/或以较慢的动力学转化为Zx。为单体重组蛋白测定的脱环氧化特性与在相同体外试验中从天然LHCI - 730和LHCI - 680分离得到的特性以及在天然LHCIs体内条件下发现的脱环氧化状态一致。
