Cox Nicholas, Hughes Joseph L, Steffen Ronald, Smith Paul J, Rutherford A William, Pace Ron J, Krausz Elmars
Research School of Chemistry, Australian National University, Canberra, ACT 0200, Australia.
J Phys Chem B. 2009 Sep 10;113(36):12364-74. doi: 10.1021/jp808796x.
Low-temperature absorption and CD spectra, measured simultaneously, are reported from Photosystem II (PS II) reduced with sodium dithionite. Spectra were obtained using PS II core complexes before and after photoaccumulation of Pheo(D1)(-), the anion of the primary acceptor. For plant PS II, Pheo(D1)(-) was generated under conditions in which the primary plastoquinone was present as an anion (Q(A)(-)) and as a modified species taken to be the neutral doubly reduced hydroquinone (Q(A)H(2)). The bleaches observed upon Pheo(D1)(-) formation in the presence of Q(A)(-) are shifted to the blue compared those in the presence of Q(A)H(2). This is attributed to the influence of the charge on Q(A)(-), and this effect mirrors the well-known electrochromic effect of Q(A)(-) on the neutral pigments. The absorption bleaches induced by Pheo(D1) reduction are species dependent. Structured changes of the CD in the 680-690 nm spectral region are seen upon photoaccumulation of Pheo(D1)(-) in PS II from plant, Synechocystis and Thermosynechococcus vulcanus. These CD changes are shown to be consistent with the overall electronic assignments of Raszewski et al. [Raszewski et al. Biophys. J. 2008, 95, 105], which place the dominant Pheo(D1) excitation near 672 nm. CD changes associated with Pheo(D1) reduction are modeled to arise from the shift and intensity changes of two CD features: one predominately of Chl(D1) character, the other predominately Pheo(D2) in character. The assignments are also shown to account for the Q(Y) absorption changes in samples where the quinone is its charged (Q(A)(-)) and neutral (Q(A)H(2)) states.
报道了用连二亚硫酸钠还原的光系统II（PS II）的低温吸收光谱和圆二色光谱（CD光谱），二者是同时测量的。光谱是使用PS II核心复合物在原初受体阴离子Pheo(D1)(-)光积累前后获得的。对于植物PS II，Pheo(D1)(-)是在原初质体醌以阴离子形式（Q(A)(-)）以及被认为是中性双还原对苯二酚（Q(A)H(2)）的修饰形式存在的条件下产生的。与在Q(A)H(2)存在时相比，在Q(A)(-)存在下Pheo(D1)(-)形成时观察到的吸收漂白向蓝光方向移动。这归因于Q(A)(-)上电荷的影响，并且这种效应反映了Q(A)(-)对中性色素的众所周知的电致变色效应。由Pheo(D1)还原引起的吸收漂白依赖于物种。在植物、集胞藻和嗜热栖热菌的PS II中，Pheo(D1)(-)光积累后，在680 - 690 nm光谱区域观察到CD的结构变化。这些CD变化与Raszewski等人[Raszewski等人，《生物物理杂志》，2008年，95卷，105页]的整体电子归属一致，该归属将主要的Pheo(D1)激发置于672 nm附近。与Pheo(D1)还原相关的CD变化被模拟为由两个CD特征的位移和强度变化引起：一个主要具有Chl(D1)特征，另一个主要具有Pheo(D2)特征。这些归属也被证明可以解释醌处于其带电（Q(A)(-)）和中性（Q(A)H(2)）状态的样品中的Q(Y)吸收变化。
