title: Characterization of a cyanobacterial photosystem I complex.
abstract: A simple procedure is described for the preparation of photosystem I (PSI) particles from Triton X-100-solubilized thylakoid membranes of the unicellular cyanobacterium Synechococcus 6301. The purified PSI complex contained the full complement of antenna chlorophylls, 130 +/- 5/P700, displayed the electron paramagnetic resonance signals characteristic of iron-sulfur centers X, A, and B, and had a protein/chlorophyll ratio of 2.9. Determination of the polypeptide composition, utilizing a uniformly 14C-labeled complex, showed that it contained polypeptides of 70, 18, 17.7, 16, and 10 kDa, in a molar ratio of 4.0:0.7:1.0:0.5:1.6. The relative amount of the lower molecular weight polypeptides showed progressive decrease with increase in Triton X-100 concentration and time of exposure to detergent. Consequently, it is proposed that in vivo the composition of the complex is [70 kDa]4 [18 kDa]1 [17.7 kDa]1 [16 kDa]1 [10 kDa]2. Relative to 130 mol of chlorophyll a, the PSI complex contained 16 mol of carotenoids, 13.7 +/- 1.0 g atoms of Fe, and 12.2 +/- 1.1 g atoms of labile sulfide. The properties of complexes fully depleted of the low-molecular weight polypeptides by treatment with sodium dodecyl sulfate or with proteinase K are also described.
authors.forename: D J
authors.initials: DJ
authors.lastname: Lundell
authors.forename: A N
authors.initials: AN
authors.lastname: Glazer
authors.forename: A
authors.initials: A
authors.lastname: Melis
authors.forename: R
authors.initials: R
authors.lastname: Malkin
mesh_terms: D002734:Chlorophyll / Q000302:isolation & purification / Q000378:metabolism*; D000458:Cyanobacteria / Q000378:metabolism*; D004578:Electron Spin Resonance Spectroscopy; D007501:Iron / Q000032:analysis; D007700:Kinetics; D008027:Light; D045342:Light-Harvesting Protein Complexes; D010084:Oxidation-Reduction; D045322:Photosynthetic Reaction Center Complex Proteins; D045331:Photosystem I Protein Complex; D010940:Plant Proteins / Q000302:isolation & purification / Q000378:metabolism*
chemical_list: D045342:Light-Harvesting Protein Complexes; D045322:Photosynthetic Reaction Center Complex Proteins; D045331:Photosystem I Protein Complex; D010940:Plant Proteins; D002734:Chlorophyll; C001785:chlorophyll P 700; D007501:Iron