title: Enrichment of a 50-kilodalton polypeptide in a photosystem II-phycobilisome particle from Porphyridium cruentum.
abstract: A 50-kDa polypeptide was obtained from photosynthetically active phycobilisome-photosystem II preparations from the red alga Porphyridium cruentum after removal of phycobiliproteins. Removal of phycobiliproteins caused destabilization of the structure of the phycobilisome-photosystem II preparations and was accompanied by a decline in photosystem II activity (oxygen-evolution and dichlorophenol-indophenol (DPIP) reduction). The treatments in increasing relative effectiveness were: addition of EDTA (10 mM), lowering the pH (6.8----4.4), and lowering the ionic strength (to ca. 1 mM phosphate). The lowering of the ionic strength by dialysis resulted in a preparation highly enriched in a 50-kDa polypeptide (apparent molecular mass on SDS-PAGE). This preparation retained photosystem II activity as evidenced by the photoreduction of DPIP in the presence of diphenylcarbazide (222 mumol DPIP/mg chlorophyll/h). Also it had a 698-nm (77K) fluorescence emission maximum, as compared to a 668-nm emission in the unfractionated preparation, which indicates enrichment of the photosystem II reaction center. Comparing our results with those obtained from green plants and a cyanobacterium leads us to suggest that the reaction center II polypeptides are highly similar in all chlorophyll alpha-containing plants.
mesh_terms: D002413:Cations, Divalent / Q000494:pharmacology; D002734:Chlorophyll / Q000032:analysis*; D004591:Electrophoresis, Polyacrylamide Gel; D006863:Hydrogen-Ion Concentration; D045342:Light-Harvesting Protein Complexes; D009994:Osmolar Concentration; D010455:Peptides / Q000302:isolation & purification*; D045322:Photosynthetic Reaction Center Complex Proteins; D045332:Photosystem II Protein Complex; D045524:Phycobilisomes; D010940:Plant Proteins / Q000032:analysis*; D000461:Rhodophyta / Q000032:analysis*
chemical_list: D002413:Cations, Divalent; D045342:Light-Harvesting Protein Complexes; D010455:Peptides; D045322:Photosynthetic Reaction Center Complex Proteins; D045332:Photosystem II Protein Complex; D045524:Phycobilisomes; D010940:Plant Proteins; D002734:Chlorophyll