Hillmann B, Brettel K, van Mieghem F, Kamlowski A, Rutherford A W, Schlodder E
Max-Volmer-Institut für Biophysikalische und Physikalische Chemie, Technische Universität Berlin, Germany.
Biochemistry. 1995 Apr 11;34(14):4814-27. doi: 10.1021/bi00014a039.
Absorbance difference spectra of the transient states in photosystem II (PS II) have been examined in the Qv absorption region between 660 and 700 nm. The P680+Pheo-/P680Pheo, 3P680/P680, and P680+QA-/P680QA spectra were measured in O2-evolving PS II core complexes from Synechococcus and PS II-enriched membrane fragments from spinach. The low-temperature absorbance difference spectra vary only slightly between both PS II preparations. The 3P680/P680 spectrum is characterized by a bleaching at 685 nm at 25 K and indicates weak exciton coupling with neighboring pigment(s). We conclude that P680 absorbs at 685 nm in more intact PS II preparations at cryogenic temperature. The difference spectra of the radical pairs are strongly temperature dependent. At low temperature the P680+QA-/P680QA- spectrum exhibits the strongest bleaching at 675 nm whereas the P680+Phe-/P680Pheo spectra show two distinct bleaching bands at 674 and 684 nm. It is suggested that an electrochronic red shift resulting in a bleaching at 675 nm and an absorbance increase at about 682 nm dominates the spectral features of the charge-separated states. On the basis of the present results and those in the literature, we conclude that the interactions between the pigments and especially the organization of the primary donor must be quite different in PS II compared to bacterial reaction centers, although the basic structural arrangement of the pigments might be similar. Spectral data obtained with samples in the presence of singly and doubly reduced QA indicate that the primary photochemistry in PS II is not strongly influenced by the redox state of QA at low temperature and confirm the results of the accompanying paper [Van Mieghem, F. J. E., Brettel, K., Hillmann, B., Kamlowski, A., Rutherford, A. W., & Schlodder, E. (1995) Biochemistry 34, 4798-4813]. The spectra of the primary radical pair and the reaction center triplet obtained with more intact PS II preparations differ widely from those of D1/D2/cyt b-559 complexes. In the latter sample, where 3P680 formation results in a bleaching at 680 nm, the P680+Pheo-/P680Pheo spectrum shows only one broad bleaching band at about 680 nm, and the main bleaching due to photoaccumulation of Pheo- at 77 K appears at 682 nm instead of 685 nm in PS II core complexes. This indicates that the removal of the core antenna which is accompanied by the loss of QA causes also structural changes of the reaction center.
在660至700nm的Qv吸收区域内，对光系统II（PS II）瞬态状态的吸光度差光谱进行了研究。在来自集胞藻的放氧PS II核心复合物和来自菠菜的富含PS II的膜片段中，测量了P680 + Pheo - /P680Pheo、3P680/P680和P680 + QA - /P680QA光谱。两种PS II制剂的低温吸光度差光谱仅略有不同。3P680/P680光谱的特征是在25K时685nm处出现漂白，表明与相邻色素存在弱激子耦合。我们得出结论，在低温下，在更完整的PS II制剂中，P680在685nm处吸收。自由基对的差光谱强烈依赖于温度。在低温下，P680 + QA - /P680QA - 光谱在675nm处表现出最强的漂白，而P680 + Phe - /P680Pheo光谱在674和684nm处显示出两个不同的漂白带。有人认为，导致675nm处漂白和约682nm处吸光度增加的电子延迟红移主导了电荷分离态的光谱特征。根据目前的结果和文献中的结果，我们得出结论，尽管色素的基本结构排列可能相似，但与细菌反应中心相比，PS II中色素之间的相互作用，尤其是初级供体的组织必须有很大不同。在单还原和双还原QA存在下用样品获得的光谱数据表明，PS II中的初级光化学在低温下不受QA氧化还原状态的强烈影响，并证实了随附论文[Van Mieghem, F. J. E., Brettel, K., Hillmann, B., Kamlowski, A., Rutherford, A. W., & Schlodder, E. (1995) Biochemistry 34, 4798 - 4813]的结果。用更完整的PS II制剂获得的初级自由基对和反应中心三重态的光谱与D1/D2/cyt b - 559复合物的光谱有很大不同。在后者的样品中，3P680的形成导致680nm处漂白，P680 + Pheo - /P680Pheo光谱在约680nm处仅显示一个宽的漂白带，并且在77K时由于Pheo - 的光积累引起的主要漂白出现在682nm处，而不是PS II核心复合物中的685nm处。这表明伴随着QA损失的核心天线的去除也导致了反应中心的结构变化。
