Abstract
Oxygen-evolving Photosystem II (crude PSII) prepared from a diatom, Chaetoceros gracilis, contained five extrinsic proteins of PsbO, PsbQ', PsbV, Psb31 and PsbU. To examine binding and functional properties of these extrinsic proteins, we purified the five extrinsic proteins and performed reconstitution experiments of these extrinsic proteins with PSII intrinsic proteins. After release of all of the extrinsic proteins by alkaline Tris-treatment of crude PSII, the five extrinsic proteins were purified by ion-exchange column chromatography. For reconstitution experiments, pure PSII prepared by DEAE column chromatography of Triton-solubilized crude PSII was treated with 4 M urea and 0.2 M NaCl to release all of the extrinsic proteins. This extrinsic protein-depleted PSII was reconstituted with each extrinsic protein either separately or in various combinations. Based on the results obtained, we will propose a model of diatom PSII showing association of the five extrinsic proteins.
