Ascorbate in thylakoid lumen functions as an alternative electron donor to photosystem II and photosystem I
Ascorbate in thylakoid lumen functions as an alternative electron donor to photosystem II and photosystem I
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DOI：
10.1016/j.abb.2004.05.022
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发表时间：
2004-09-01
影响因子：
3.9
通讯作者：
Asada, K
中科院分区：
文献类型：
--
作者：
Mano, J;Hideg, É;Asada, K
研究了抗坏血酸（Asc）在类囊体腔中支持光合电子传递的作用。Asc在光系统（PS） II和PSI中可被光氧化。当水氧化酶复合物（WOC）被酸性pH或UV-B灭活时，Asc在PSII中被光氧化，Asc取代水成为电子供体。表观K-m为2.5 mM。在20 mM Asc时，电子传递速率达到50 μ mol NADP+还原mg Chl(-1) h（-1）。Asc不被具有活性WOC的PSII反应中心复合物氧化，因此仅在WOC失活时作为紧急供体发挥作用。在3-（3,4-二氯苯基）-1,1'-二甲基脲存在下，Asc被PSI光氧化，在50 mM Ase中具有较低的亲和力和70 μ mol NADP+-还原mg Chl(-1) h（-1）的电子传递速率。因此，Asc可以在生理相关范围内的Asc浓度下以相当高的速率支持psi介导的电子流。在PSI光氧化Ase的过程中，我们观察到单脱氢抗坏血酸自由基（MDA）的产生，该自由基不被外源添加的MDA还原酶清除。Asc对P700（+）的还原不受氰化物灭活质体青素的影响。这些结果表明Asc在PSI的管腔侧被P700（+）直接单价氧化。通过9-氨基吖啶荧光测定，电子传递Asc—> PSI—> NADP+没有在类囊体膜上形成质子梯度。基于这些结果，我们提出当线性电子传递部分受损时，asc依赖的循环电子流可以在PSI周围运行，并且可以通过PSI和PSII运行。(C) 2004爱思唯尔公司版权所有。
The roles of ascorbate (Asc) in the thylakoid lumen to support photosynthetic electron transport are investigated. Asc can be photooxidized in photosystem (PS) II and PSI. When the water oxidase complex (WOC) was inactivated by acidic pH or by UV-B, Asc was photooxidized in PSII with Asc replacing water as the electron donor. An apparent K-m was 2.5 mM. At 20 mM Asc, the electron transport rate reached 50 mumol NADP+-reduced mg Chl(-1) h(-1). Asc was not oxidized by the PSII reaction center complex having an active WOC, and hence was suggested to function as an emergency donor only when WOC is inactivated. In the presence of 3-(3,4-dichlorophenyl)-1,1'-dimethylurea, Asc was photooxidized by PSI, with a lower affinity and an electron transport rate of 70 mumol NADP+-reduced mg Chl(-1) h(-1) in 50 mM Ase. Thus, Asc can support a PSI-mediated electron flow at a reasonably high rate at Asc concentrations in the physiologically relevant range. During the photooxidation of Ase by PSI, we observed the production of the monodehydroascorbate radical (MDA) that was unscavenged by the exogenously added MDA reductase. Reduction of P700(+) by Asc was not affected by the inactivation of plastocyanin with cyanide. These results indicated that Asc was univalently oxidized on the lumenal side of PSI, directly by P700(+). The electron transport Asc --> PSI --> NADP+ did not form a proton gradient across the thylakoid membrane, as determined by 9-aminoacridine fluorescence. Based on these results, we propose that the Asc-dependent cyclic electron flow around PSI, and that through both PSI and PSII can operate when the linear electron transport is partially impaired. (C) 2004 Elsevier Inc. All rights reserved.