title: Further purification of "Triton subchloroplast fraction I" (TSF-I particles). Isolation of a cytochrome-free high-P-700 particle and a complex containing cytochromes f and b6, plastocyanin and iron-sulfur protein(s).
abstract: The "Triton Subchloroplast Fraction I" or "TSF-I particles" can be further fractionated into a cytochrome fraction and a P-700-containing fraction essentially free of cytochromes. The cytochrome complex contains cytochromes f and b6 in approx. equimolar amounts, and, in addition, also plastocyanin and one iron-sulfur protein, all in the bound state. Bound plastocyanin was characterized by EPR spectroscopy. The EPR spectrum of the bound iron-sulfur protein resembles that previously detected in Phostosystem I particles under highly reducing conditions at lower than -560 mV. The redox potential of P-700 in the cytochrome-free high-P-700 particles was measured to be +468 mV; those of cytochromes f and b6 are +345 and -140 mV, respectively. Among the four components present in the complex, only cytochrome f can be coupled to a Photosystem I particle and undergoes photooxidation. This coupled photooxidation is totoally inhibited by KCN and only partially inhibited by HgCl2. The similarity of the complex containing cytochromes f and b6, plastocyanin, and an iron-sulfur protein to complexes III and IV of the mitochondrial respiratory redox chain and a possible involvement of the complex in cyclic photophosphorylation are noted and discussed.
mesh_terms: D001665:Binding Sites; D002458:Cell Fractionation; D002736:Chloroplasts / Q000032:analysis* / Q000648:ultrastructure; D003300:Copper / Q000032:analysis; D003580:Cytochromes / Q000032:analysis*; D004578:Electron Spin Resonance Spectroscopy; D007501:Iron / Q000032:analysis; D008667:Metalloproteins / Q000032:analysis*; D010084:Oxidation-Reduction; D010940:Plant Proteins / Q000032:analysis*; D010944:Plants; D010970:Plastocyanin / Q000032:analysis*; D011092:Polyethylene Glycols; D011485:Protein Binding; D011487:Protein Conformation; D013053:Spectrophotometry; D013455:Sulfur / Q000032:analysis
chemical_list: D003580:Cytochromes; D008667:Metalloproteins; D010940:Plant Proteins; D011092:Polyethylene Glycols; D013455:Sulfur; D003300:Copper; D010970:Plastocyanin; D007501:Iron