Büchel C, Barber J, Ananyev G, Eshaghi S, Watt R, Dismukes C
Biochemistry Department, Imperial College of Science, Technology and Medicine, London SW7 2AY, United Kingdom.
Proc Natl Acad Sci U S A. 1999 Dec 7;96(25):14288-93. doi: 10.1073/pnas.96.25.14288.
Isolated subcomplexes of photosystem II from spinach (CP47RC), composed of D1, D2, cytochrome b(559), CP47, and a number of hydrophobic small subunits but devoid of CP43 and the extrinsic proteins of the oxygen-evolving complex, were shown to reconstitute the Mn(4)Ca(1)Cl(x) cluster of the water-splitting system and to evolve oxygen. The photoactivation process in CP47RC dimers proceeds by the same two-step mechanism as observed in PSII membranes and exhibits the same stoichiometry for Mn(2+), but with a 10-fold lower affinity for Ca(2+) and an increased susceptibility to photodamage. After the lower Ca(2+) affinity and the 10-fold smaller absorption cross-section for photons in CP47 dimers is taken into account, the intrinsic rate constant for the rate-limiting calcium-dependent dark step is indistinguishable for the two systems. The monomeric form of CP47RC also showed capacity to photoactivate and catalyze water oxidation, but with lower activity than the dimeric form and increased susceptibility to photodamage. After optimization of the various parameters affecting the photoactivation process in dimeric CP47RC subcores, 18% of the complexes were functionally reconstituted and the quantum efficiency for oxygen production by reactivated centers approached 96% of that observed for reconstituted photosystem II-enriched membranes.
从菠菜中分离出的光系统II亚复合物（CP47RC），由D1、D2、细胞色素b(559)、CP47以及一些疏水小亚基组成，但不含CP43和放氧复合体的外在蛋白，已被证明能够重构水裂解系统的Mn(4)Ca(1)Cl(x)簇并释放氧气。CP47RC二聚体中的光激活过程通过与在PSII膜中观察到的相同的两步机制进行，并且对Mn(2+)表现出相同的化学计量，但对Ca(2+)的亲和力低10倍，且对光损伤的敏感性增加。考虑到CP47二聚体中较低的Ca(2+)亲和力和对光子的吸收截面小10倍的情况后，两个系统中限速钙依赖性暗步骤的内在速率常数没有区别。CP47RC的单体形式也显示出光激活和催化水氧化的能力，但活性低于二聚体形式，且对光损伤的敏感性增加。在优化影响二聚体CP47RC亚核心中光激活过程的各种参数后，18%的复合物在功能上得以重构，并且重新激活的中心产生氧气的量子效率接近重构的富含光系统II的膜所观察到的量子效率的96%。
