Abstract
The water-oxidizing reaction in the oxidizing side of Photosystem 2 (PS2) is catalyzed by the manganese cluster. A minimum size of the water-oxidizing complex still remains to be unsolved, although its functional unit is considered to consist of PS2 protein components such as two reaction center proteins, the chlorophyll-binding proteins, Cyt b559 and PS2 extrinsic proteins.
We treated spinach PS2 membranes with sucrose monolaurate (SML), to isolate the PS2 core complexes depleted of CP43 and the functional manganese cluster. The low-molecular-mass intrinsic proteins containing L protein (designated as SML extracts) were also isolated during a preparation process of PS2 core complexes. The L protein seems to function in QA activity. Thus, we reconstituted PS2 core complexes with SML extracts, resulting in repair of both the reducing and oxidizing side of PS2. Furthermore, followed by photoactivation of these reconstituted preparations, restoration of the water-oxidizing activity was obtained.
