ELECTRON-TRANSFER IN PHOTOSYSTEM-II AT CRYOGENIC TEMPERATURES
ELECTRON-TRANSFER IN PHOTOSYSTEM-II AT CRYOGENIC TEMPERATURES
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DOI：
10.1021/bi00348a042
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发表时间：
1985-12-31
期刊：
影响因子：
2.9
通讯作者：
BRUDVIG, GW
中科院分区：
文献类型：
--
作者：
DEPAULA, JC;INNES, JB;BRUDVIG, GW
耶鲁大学化学系，纽黑文，康涅狄格州06511接收1985年6月14日摘要：光化学在光系统II的菠菜已被其特征在于电子顺磁共振（EPR）光谱在77-235 K的温度范围内，和光氧化物种的产量已被确定通过整合theirEPR信号。在用3-（3，4-二氯苯基）-1，1-二甲基脲（DCMU）处理的样品中，Fe（II）-QA-EPR信号的恒定产率反映了在整个研究的温度范围内发生单一稳定的电荷分离。然而，观察到三个不同的电子捐赠途径。低于100 K，每个反应中心光氧化一个细胞色素<$559分子。在100和200 K之间，细胞色素b559和Sj状态竞争电子捐赠给P680+。St态的光氧化通过两个中间体发生：g= 4.1的EPR信号物质首先由凯西和绍尔报道[凯西，J. L，&绍尔，K.（1984）Biochim. Biophys. Acta 767，21-28]在100和160 K之间被光氧化，并且在黑暗中加热到200 K时，该EPR信号产生与S2态相关的多线EPR信号。在200 K或更高温度下，只有S1态向P680+提供电子，从而产生光诱导的S2态多线EPR信号。这些结果表明，最大的S2态多线EPR信号占反应中心浓度的100%。在样品中，电子捐赠细胞色素b559被阻止化学氧化，在77 K的照明产生的自由基，可能是叶绿素阳离子，占95%的反应中心浓度。在100 K以下，该电子供体与S3态竞争向P680+的电子供体。然而，细胞色素<$559的化学氧化对g= 4.1或多线EPR信号物质的光氧化没有影响。通过化学氧化产生的细胞色素b559 EPR信号的定量表明，每个反应中心存在两个细胞色素b559分子。在190 K以上光照时，样品发生了S2- S3转变。然而，没有检测到g= 4.1的EPR信号作为S2-S3转变的中间体。我们建议，g= 4.1和多线EPR信号都产生于相同的网站在S2氧化态和光谱的差异反映了温度依赖性的结构变化的Mn活性位点。在植物、藻类和蓝藻中，H20光氧化成O2是由光系统II（PSII）的O2释放复合物（OEC）1催化的。该过程所需的四种氧化当量通过PSII反应中心中的连续电荷分离产生，并逐步储存在OEC中，其可以以称为Si·（t=0-4）态的五种中间氧化态存在（Kok等人，1970年）。S 0和S1状态是暗稳定的，并且在短期暗适应的类囊体和PSII膜中以1：3的比例存在（Forbush等人，1971年）。Velthuys & Visser（1975）、Vermaas等人的研究。（1984）和Hanssum et al.（1985）表明，长期黑暗孵育改变了S 0：S！比例基本上为0：1。该过程的机制尚不清楚，但它可能涉及OEC的逆转录（Beck等人，1985年）。氧化还原活性位点的身份正在慢慢解开。锰参与O2的演化[综述见Amesz（1983）]和Dismukes & Siderer（1981）发现的多线S2态EPR信号（这是交换偶联锰络合物的特征）表明，OEC的催化位点可能由四个锰离子组成，这些锰离子的位置很近。
Department of Chemistry, Yale University, New Haven, Connecticut 06511 Received June 14, 1985 abstract: The photochemistry in photosystem II of spinach has been characterized by electron paramagnetic resonance(EPR) spectroscopy in the temperature range of 77-235 K, and the yields of the photooxidized species have been determined by integration of theirEPR signals. In samples treated with 3-(3, 4-dichlorophenyl)-1, 1-dimethylurea (DCMU), a single stable charge separation occurred throughout the tem-perature range studied as reflected by the constant yield of the Fe (II)-QA-EPR signal. Threedistinct electron donation pathways were observed, however. Below 100 K, one molecule of cytochrome¿> 559 was photooxidized per reaction center. Between 100 and 200 K, cytochrome b559 and the Sj state competed for electron donation to P680+. Photooxidation of the St state occurred via two intermediates: the g= 4.1 EPR signal species first reported by Casey and Sauer [Casey, J. L, & Sauer, K.(1984) Biochim. Biophys. Acta 767, 21-28] was photooxidized between 100 and 160 K, and upon being warmed to 200 K in the dark, this EPR signal yielded the multiline EPR signal associated with the S2 state. Only the S, state donated electrons to P680+ at 200 K or above, giving rise to the light-induced S2-state multiline EPRsignal. These results demonstrate that the maximum S2-state multiline EPR signal accounts for 100% of the reaction center concentration. In samples where electrondonation from cytochrome b559 was prevented by chemical oxidation, illumination at 77 K produced a radical, probably a chlorophyll cation, which accounted for 95% of the reaction center concentration. This electron donor competed with the S3 state for electron donation to P680+ below 100 K. Chemical oxidation of cytochrome¿> 559, however, had no effect on the photooxidation of the g= 4.1 or multiline EPR signal species. Quantitation of the cytochrome b559 EPR signal produced by chemical oxidation showed that two molecules of cytochrome b559 are present per reaction center. The S2- S3 transition occurred in samples illuminated above 190 K. The g= 4.1 EPR signal was not detected, however, as an intermediate in the S2—S3 transition. We propose that the g= 4.1 and multiline EPR signals both arise from the same site in the S2 oxidation state and the spectroscopic differences reflect temperature-dependent structural changes in the Mn active site. e photooxidation ofH20 to 02 in plants, algae, and cya-nobacteria is catalyzed by the 02-evolving complex (OEC) 1 of photosystem II (PSII). The four oxidizingequivalents necessary for this process are created by successive charge separations in the PSII reaction center and stored stepwise in the OEC, which can exist in five intermediate oxidation states called S,·(t=0-4) states (Kok et al., 1970). The S0 and S, states are dark-stable and present in a ratio of 1: 3 in short-term dark-adapted thylakoid and PSII membranes (Forbush et al., 1971). Studies by Velthuys & Visser (1975), Vermaas et al.(1984), and Hanssum et al.(1985) indicate that long-term dark incubation changes the S0: S! ratio to essentially 0: 1. The mechanism for this process is not known, but it may involve reverse turnover of the OEC (Beck et al., 1985). The identities of the redox active sites are slowly being unraveled. The involvement of manganese in 02 evolution [for a review, see Amesz (1983)] and the discovery by Dismukes & Siderer (1981) of a multiline S2-state EPR signal, which is characteristic of an exchange-coupled manganese complex, suggest that the catalytic site the OEC mayconsist of as many as four manganese ions in close …