Location of chlorophyllZ in photosystem II.
Location of chlorophyllZ in photosystem II.
复制标题
叶绿素Z在光系统II中的位置。
DOI：
10.1021/bi00205a018
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发表时间：
1994
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：
Koulougliotis,D;Innes,JB;Brudvig,GW
饱和恢复和渐进式微波功率饱和EPR光谱已被用来探测叶绿素”1”（Chlz+）自由基物种在耗尽光系统II（PSII）的位置。Chlz+的自旋-晶格弛豫瞬态是非单指数的，由于偶极-偶极相互作用与PSII中的其他顺磁中心之一。对经CN_2处理的贫CN_2的PSII膜样品（其中非血红素Fe（II）转化为低自旋抗磁性形式）的测量证实，非血红素Fe（II）引起Chlz+的偶极弛豫增强。将饱和度-恢复EPR数据拟合至偶极模型[Hirsh，DJ，Beck，W. F.、Innes，J. B.，& Brudvig，G. W.（1992）Biochemistry 31，532]，其考虑了对自由基的自旋-晶格弛豫的各向同性（标量）和取向依赖性（偶极）贡献。Chlz”1”的偶极速率常数的温度依赖性是相同的温度依赖性最近观察到的稳定的酪氨酸自由基，Yd*，和特殊的对细菌叶绿素自由基，（BChla）2+，在PSII和反应中心从Rhodobacter sphaeroides，分别。由于非血红素Fe（II）已知在后两种情况下引起自由基的偶极弛豫增强，因此该结果提供了非血红素Fe（II）引起Chlz”1”的偶极弛豫增强的进一步证据，并且，此外，证明非血红素Fe（II）在PSII和来自球形红细菌的反应中心中的磁性非常相似。通过使用已知的Fe（II）-（BChla）2+距离进行校准，我们估计Fe（II）-Chlz+距离为39.5±2.5 μ m。由外源Dy 3+络合物引起的自由基的偶极弛豫增强理论[Innes，J. B.，& Brudvig，G. W.（1989）Biochemistry 28，1116]也被用于确定Chlz”1”相对于PSII蛋白表面的位置。Chlz”1”在外源性多肽缺失的PSII膜中位于与腔蛋白和基质蛋白表面的距离大致相等的位置。这些结果提供了第一个直接的证据，反对Chlz的分配Chi单体类似于“偷窥”BChl在细菌反应中心和点组氨酸-118在DI和D2蛋白作为潜在的配体Chlz-光系统II（PSII）是一个多组分的跨膜复合物的蛋白质和发色团whichutilizes光能启动电子转移反应和氧化水分子氧。其氧化的初级电子供体P680+[一种特殊的叶绿素（Chi）]是光合作用中最强的氧化剂，具有高到足以氧化其自身天线叶绿素的还原电位[Em估计为~ 1.12 V（Klimov et al.，1980）]。PSII中的主要供电子途径是从四核Mn簇通过被称为Yz（D1多肽的Tyr-161）的酪氨酸残基到P680+，并且它涉及H2O到分子氧的催化氧化。除了这一途径，P680+至少还有两种电子供体：细胞色素559（cyt <$559）和具有氧化还原活性的酪氨酸Yo（D2多肽的Tyr-160）。最近的研究
Revised Manuscript Received June 28, 1994* abstract: Saturation-recovery and progressive microwave power saturation EPR spectroscopies have been used to probe the location of the chlorophyllz" 1"(Chlz+) radical species in-depleted photosystem II (PSII). The spin-lattice relaxation transients of Chlz+ were non-single-exponential due to a dipole-dipole interaction with one of the other paramagnetic centers inPSII. Measurements on CN_-treated,-depleted PSII membrane samples, in which the non-heme Fe (II) is converted into its low-spin, diamagnetic form, confirmed that the non-heme Fe (II) caused the dipolar relaxation enhancement of Chlz+. The saturation-recovery EPR data were fit to a dipolar model [Hirsh, DJ, Beck, W. F., Innes, J. B., & Brudvig, G. W.(1992) Biochemistry 31, 532] which takes into account the isotropic (scalar) and orientation-dependent (dipolar) contributions to the spin-lattice relaxation of the radical. The temperature dependence of the dipolar rate constants of Chlz" 1" was identical to the temperature dependencies recently observed for the stable tyrosine radical, Yd*, and the special pair bacteriochlorophyll radical,(BChla) 2+, in PSII and in reaction centers from Rhodobacter sphaeroides, respectively. Because the non-heme Fe (II) is known to cause a dipolar relaxation enhancement of the radicalsin both of the latter cases, this result provides further evidence that the non-heme Fe (II) causes the dipolar relaxation enhancement of Chlz" 1" and, moreover, demonstrates that the magnetic properties of the non-heme Fe (II) in PSII and in reaction centers from Rhodobacter sphaeroides are very similar. By using the known Fe (II)-(BChla) 2+ distance for calibration, we estimate the Fe (II)-Chlz+ distance to be 39.5±2.5 Á. The theory of dipolar relaxation enhancement of a free radical caused by exogenous Dy3+ complexes [Innes, J. B., & Brudvig, G. W.(1989) Biochemistry28, 1116] has also been applied to determine the location of Chlz" 1" relative to the PSII protein surfaces. Chlz" 1" was found to be located at approximately equaldistances from both the luminal and stromal protein surfaces in extrinsic polypeptide-depleted PSII membranes. These results provide the first direct evidence against the assignment of Chlz to a Chi monomer analogous to the “voyeur” BChl in the bacterial reaction center and point to histidines-118 in the DI and D2 proteins as potential ligands of Chlz-Photosystem II (PSII) is a multicomponent membrane-spanning complex of proteins and chromophores whichutilizes light energy to initiate electron-transferreactions and oxidize water to dioxygen. Its oxidized primary electron donor, P680+[a special chlorophyll (Chi)], is the most powerful oxidant in photosynthesis, having a reduction potential high enoughto oxidize its own antenna chlorophyll [Em is estimated to be~ 1.12 V (Klimov et al., 1980)]. The major electron-donation pathway in PSII is from a tetranuclear Mn cluster through a tyrosine residue known as Yz (Tyr-161 of the D1 polypeptide) to P680+, and it involves the catalyzed oxidation of H2O to dioxygen. In addition to this path, there exist at least two alternative electron donors to P680+: cytochrome¿> 559(cyt¿ 559) and a redox-active tyrosine, Yo (Tyr-160oftheD2 polypeptide). Recent studies