Leuschner C, Bricker T M
Department of Plant Biology, Louisiana State University, Baton Rouge 70803, USA.
Biochemistry. 1996 Apr 9;35(14):4551-7. doi: 10.1021/bi9522615.
The 33 kDa extrinsic protein of photosystem II acts to enhance oxygen evolution and to stabilize the manganese cluster at low chloride concentrations. Due to controversies concerning the stoichiometry of this protein [Miyao, M., & Murata, N. (1989) Biochim. Biophys. Acta 977, 315-321, versus Xu, Q., & Bricker, T. M. (1992) J. Biol. Chem. 267. 25816-25821] we have examined the rebinding of this protein to PS II membrane preparations which contain four, two, or zero manganese per photosystem II reaction center. After rebinding, immunoquantification of the 33 kDa extrinsic protein demonstrated that each of these photosystem II membrane preparations strongly bound two copies of the 33 kDa extrinsic protein per photosystem II reaction center. The first and second stoichiometric binding constants (Ka1 and Ka2) for the binding of the 33 kDa protein to PS II centers containing four manganese were 0.42 and 0.67 nM(-1), respectively. Disruption of the manganese cluster either by removal of the chloride-sensitive manganese or extraction of the manganese cluster by alkaline Tris led to a 5-6-fold decrease in Ka1 and about a 3-fold decrease in Ka2. In all cases the binding of the two copies of the 33 kDa extrinsic protein exhibited positive cooperativity with Hill coefficients ranging from 1.6 to 2.2. These findings demonstrate that damage to the manganese cluster alters the binding affinity of the 33 kDa extrinsic protein to photosystem II but does not alter the molecularity of the binding reaction.
光系统II的33 kDa外在蛋白可增强氧气释放，并在低氯浓度下稳定锰簇。由于关于该蛋白化学计量的争议[宫尾，M.，& 村田，N.（1989年）《生物化学与生物物理学报》977，315 - 321，与徐，Q.，& 布里克，T. M.（1992年）《生物化学杂志》267，25816 - 25821]，我们研究了该蛋白与每个光系统II反应中心含四个、两个或零个锰的PS II膜制剂的重新结合。重新结合后，对33 kDa外在蛋白的免疫定量表明，这些光系统II膜制剂中的每一种都能强烈地将两个拷贝的33 kDa外在蛋白结合到每个光系统II反应中心。33 kDa蛋白与含四个锰的PS II中心结合的第一和第二化学计量结合常数（Ka1和Ka2）分别为0.42和0.67 nM(-1)。通过除去对氯敏感的锰或用碱性Tris提取锰簇来破坏锰簇，导致Ka1降低5 - 6倍，Ka2降低约3倍。在所有情况下，两个拷贝的33 kDa外在蛋白的结合都表现出正协同性，希尔系数范围为1.6至2.2。这些发现表明，锰簇的损伤改变了光系统II的33 kDa外在蛋白的结合亲和力，但没有改变结合反应的分子数。
