Abstract
It has not been clarified what is a minimum size of the water-oxidizing complex. Accordingly,whether PS2 chlorophyll proteins of CP43 and CP47 and other factors are required for the photoassembly of the Mn cluster remains to be proved.
By treating spinach PS2 membranes with 0.8M Tris (pH8.0) and sucrose monolaurate (SML), we isolated the PS2 core complexes depleted of CP43 and the functional manganese cluster. The low-molecular-mass intrinsic proteins were also purified from the SML extract freed of PS2 core complexes during their isolation procedure. Thus, we reconstituted PS2 core complexes with small intrinsic proteins and lipids (PG,DGDG,plastoquinone etc), resulting in increase of electron transfer activity around the PS2 and appearance of the high-affinity Mn-binding site. These results indicate the small intrinsic proteins/lipids are essential for both sides of PS2. We are now investigating the roles of PS2 small intrinsic proteins/lipids on photoactivation of the water-oxidizing reaction.
