A new 4.8-kDa polypeptide intrinsic to the PSII reaction center, as revealed by modified SDS-PAGE with improved resolution of low-molecular-weight proteins. Plant Cell Physiol

Low-molecular-weight polypeptides in various PS II preparations from spinach and wheat were analyzed by modified SDS-PAGE, which gave good resolution of low-molecular-weight pro-teins with minimized interference by lipids. PS II membrane fragments contained at least nine low-molecular-weight polypeptides of between 3.9 kDa and 11 kDa, and all of them were identifi-ed in thylakoid membranes. Of these nine polypeptides, the 10-kDa phosphoprotein, the 5-kDa, 4.8-kDa, and 4.1-kDa polypeptides, and the two subunits of cytochrome b559 were commonly found in O2-evolving core complexes of wheat and spinach. In contrast, PS II reaction center complexes that consisted of Dl, D2 and two cytochrome b559 polypeptides retained only the 4.8-kDa polypeptide. Analysis by Western blotting revealed that the 4.8-kDa polypeptide is an intrin-sic component of the PS II reaction center. Key words: Low-molecular-weight polypeptide — Photosystem II — Reaction center — SDS-ge