Kim S, Pichersky E, Yocum C F
Department of Biology, University of Michigan, Ann Arbor 48109.
Biochim Biophys Acta. 1994 Dec 30;1188(3):339-48. doi: 10.1016/0005-2728(94)90054-x.
An intrinsic 22 kDa polypeptide is associated with the O2-evolving Photosystem II core complex in a variety of green plants, although it does not appear to be required for O2 evolution. Digestion of thylakoid membranes and isolated Photosystem II preparations with trypsin, followed by immunoblotting using spinach anti-22 kDa antibodies, leads to two observations: (1) the domain between the 2nd and 3rd transmembrane helices of the 22 kDa protein is stromally exposed, and (2) only in a reaction center complex preparation, lacking the chlorophyll a/b-light harvesting complex II, is there extensive proteolytic cleavage of the 22 kDa protein. We also found that after, but not prior to, selective extraction of the 22 and 10 kDa proteins from Photosystem II membranes, the chlorophyll a/b-light harvesting complex II can be separated from the Photosystem II reaction center core by precipitation with MgCl2. This result suggests that the 22 kDa polypeptide is located between the Photosystem II reaction center polypeptides and light-harvesting complex II; it is possible that the protein serves as a link between the two protein complexes. The presence of the 22 kDa protein in several species was also examined by immunoblotting with polyclonal spinach anti-22 kDa antibodies.
一种内在的22 kDa多肽与多种绿色植物中进行氧气释放的光系统II核心复合物相关联，尽管氧气释放似乎并不需要它。用胰蛋白酶消化类囊体膜和分离的光系统II制剂，然后使用菠菜抗22 kDa抗体进行免疫印迹，得到了两个观察结果：（1）22 kDa蛋白的第2和第3个跨膜螺旋之间的结构域暴露于基质中，（2）只有在缺乏叶绿素a/b捕光复合物II的反应中心复合物制剂中，22 kDa蛋白才会有广泛的蛋白水解切割。我们还发现，从光系统II膜中选择性提取22 kDa和10 kDa蛋白之后（而不是之前），叶绿素a/b捕光复合物II可以通过用MgCl2沉淀与光系统II反应中心核心分离。这一结果表明，22 kDa多肽位于光系统II反应中心多肽和捕光复合物II之间；该蛋白有可能作为这两种蛋白复合物之间的连接物。还使用菠菜抗22 kDa多克隆抗体通过免疫印迹检测了几种物种中22 kDa蛋白的存在情况。
