Department of Physiology, University of Illinois at Urbana-Champaign, 289 Morrill Hall, 505 South Goodwin Avenue, Urbana, IL 61801.
Proc Natl Acad Sci U S A. 1985 Sep;82(18):6119-23. doi: 10.1073/pnas.82.18.6119.
We present a model of photosynthetic water oxidation that utilizes the property of higher-valent Mn ions in two different environments and the characteristic function of redox-active ligands to explain all known aspects of electron transfer from H(2)O to Z, the electron donor to P680, the photosystem II reaction center chlorophyll a. There are two major features of this model. (i) The four functional Mn atoms are divided into two groups of two Mn each: [Mn] complexes in a hydrophobic cavity in the intrinsic 34-kDa protein; and (Mn) complexes on the hydrophilic surface of the extrinsic 33-kDa protein. The oxidation of H(2)O is carried out by two [Mn] complexes, and the protons are transferred from a [Mn] complex to a (Mn) complex along the hydrogen bond between their respective ligand H(2)O molecules. (ii) Each of the two [Mn] ions binds one redox-active ligand (RAL), such as a quinone (alternatively, an aromatic amino acid residue). Electron transfer occurs from the reduced RAL to the oxidized Z. When the experimental data concerning atomic structure of the water-oxidizing center (WOC), electron transfer between the WOC and Z, the electronic structure of the WOC, the proton-release pattern, and the effect of Cl(-) are compared with the predictions of the model, satisfactory qualitative and, in many instances, quantitative agreements are obtained. In particular, this model clarifies the origin of the observed absorption-difference spectra, which have the same pattern in all S-state transitions, and of the effect of Cl(-)-depletion on the S states.
我们提出了一个光合作用水氧化的模型，该模型利用了两种不同环境中高价锰离子的特性和氧化还原活性配体的特征功能，解释了从 H2O 到 P680 的电子供体 Z 的电子转移的所有已知方面，这是光系统 II 反应中心叶绿素 a。该模型有两个主要特点。(i) 四个功能 Mn 原子被分成两组，每组两个 Mn：内在 34 kDa 蛋白疏水区中的[Mn]复合物；和外在 33 kDa 蛋白亲水表面上的 (Mn) 复合物。H2O 的氧化由两个 [Mn] 复合物完成，质子通过它们各自配体 H2O 分子之间的氢键从一个 [Mn] 复合物转移到另一个 (Mn) 复合物。(ii) 两个 [Mn] 离子中的每一个都结合一个氧化还原活性配体 (RAL)，如醌（或者，芳香族氨基酸残基）。电子从还原的 RAL 转移到氧化的 Z。当涉及水氧化中心 (WOC) 的原子结构、WOC 和 Z 之间的电子转移、WOC 的电子结构、质子释放模式以及 Cl(-)的影响的实验数据与模型的预测进行比较时，会得到令人满意的定性和定量的一致性。特别是，该模型澄清了观察到的吸收差光谱的起源，这些光谱在所有 S 态跃迁中具有相同的模式，以及 Cl(-)耗竭对 S 态的影响。
