Two chlorophyll-binding subunits of the photosystem 2 reaction center complex isolated from the thermophilic cyanobacterium Synechococcus sp.
The reaction center of photosystem 2 has been highly purified from digitonin-solubilized thylakoid membranes of the thermophilic cyanobacterium Synechococcus sp. by means of sucrose density gradient centrifugation and electrophoresis on polyacrylamide gels containing digitonin. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis of isolated reaction center complex yielded four chlorophyll a proteins named CP2-a, CP2-b, CP2-c, and CP2-d. When reelectrophoresed, CP2-a was transformed to CP2-d, and CP2-b was converted to CP2-a and CP2-d. The reaction center complex consisted of two major polypeptides of 47,000 and 40,000 Da and several minor polypeptides. CP2-b contained a 47,000-Da polypeptide together with 66,000- and 31,000-Da polypeptides, while CP2-a and CP2-d had only a 47,000-Da polypeptide. The apoprotein of CP2-c was a 40,000-Da polypeptide. Absorption spectra of CP2-a, -b, and -d were similar to each other but distinctly different from those of CP2-c at liquid nitrogen temperature. The reaction center complex showed two fluorescence emission bands at 686 and 694 nm at 77 degrees K. CP2-a, -b, and -d emitted the band at 694 nm, whereas the fluorescence peak at 686 nm was associated with CP2-c. It is concluded that the photosystem 2 reaction center complex contains two chlorophyll-binding subunits, CP2-d (or CP2-a) which may be the site of the primary photochemistry of photosystem 2 and CP2-c which may function as the antenna of the reaction center of photosystem 2.
D002734:Chlorophyll / Q000302:isolation & purification / Q000378:metabolism*; D000458:Cyanobacteria / Q000378:metabolism*; D004591:Electrophoresis, Polyacrylamide Gel; D005615:Freezing; D006358:Hot Temperature; D007425:Intracellular Membranes / Q000378:metabolism; D007700:Kinetics; D045342:Light-Harvesting Protein Complexes; D046911:Macromolecular Substances; D008970:Molecular Weight; D010455:Peptides / Q000302:isolation & purification; D045322:Photosynthetic Reaction Center Complex Proteins; D010940:Plant Proteins / Q000302:isolation & purification / Q000378:metabolism*; D013053:Spectrophotometry
D045342:Light-Harvesting Protein Complexes; D046911:Macromolecular Substances; D010455:Peptides; D045322:Photosynthetic Reaction Center Complex Proteins; D010940:Plant Proteins; D002734:Chlorophyll