Institut de Biologie Physico-Chimique, 13 rue Pierre et Marie Curie, 75005, Paris, France.
Photosynth Res. 1993 Jan;38(3):279-96. doi: 10.1007/BF00046752.
Old and very recent experiments on the extent and the rate of proton release during the four reaction steps of photosynthetic water oxidation are reviewed. Proton release is discussed in terms of three main sources, namely the chemical production upon electron abstraction from water, protolytic reactions of Mn-ligands (e.g. oxo-bridges), and electrostatic response of neighboring amino acids. The extent of proton release differs between the four oxidation steps and greatly varies as a function of pH both, but differently, in thylakoids and PS II-membranes. Contrastingly, it is about constant in PS II-core particles. In any preparation, and on most if not all reaction steps, a large portion of proton transfer can occur very rapidly (<20 μs) and before the oxidation of the Mn-cluster by Yz (+) is completed. By these electrostatically driven reactions the catalytic center accumulates bases. An additional slow phase is observed during the oxygen evolving step, S3⇒S4→S0. Depending on pH, this phase consists of a release or an uptake of protons which accounts for the balance between the number of preformed bases and the four chemically produced protons. These data are compatible with the hypothesis of concerted electron/proton-transfer to overcome the kinetic and energetic constraints of water oxidation.
回顾了光合作用水氧化四个反应步骤中质子释放的程度和速率的古老和最新实验。质子释放是根据三个主要来源讨论的，即从水中抽离电子后的化学产物、Mn-配体的质子反应（例如氧桥）以及相邻氨基酸的静电响应。质子释放的程度在四个氧化步骤中不同，并且在类囊体和 PS II 膜中均随 pH 值而大大变化，但方式不同。相比之下，在 PS II 核心颗粒中基本保持不变。在任何制剂中，并且在大多数（如果不是全部）反应步骤中，很大一部分质子转移可以非常迅速（<20 μs）发生，并且在 Mn 簇被 Yz (+) 氧化完成之前。通过这些静电驱动的反应，催化中心积累碱基。在产氧步骤 S3 ⇒S4→S0 期间观察到另外一个缓慢的阶段。根据 pH 值的不同，该阶段包括质子的释放或吸收，这解释了预先形成的碱基数量和四个化学产生的质子之间的平衡。这些数据与协同电子/质子转移假说一致，以克服水氧化的动力学和能量限制。
