title: Photosystem I charge separation in the absence of centers A and B. II. ESR spectral characterization of center 'X' and correlation with optical signal 'A2'.
abstract: The Photosystem I electron acceptor complex was characterized by optical flash photolysis and electron spin resonance (ESR) spectroscopy after treatment of a subchloroplast particle with lithium dodecyl sulfate (LDS). The following properties were observed after 60 s of incubation with 1% LDS followed by rapid freezing. (i) ESR centers A and B were not observed during or after illumination of the sample at 19 K, although the P-700+ radical at g = 2.0026 showed a large, reversible light-minus-dark difference signal. (ii) Center 'X', characterized by g factors of 2.08, 1.88 and 1.78, exhibited reversible photoreduction at 8 K in the absence of reduced centers A and B. (iii) The backreaction kinetics at 8 K between P-700, observed at g = 2.0026, and center X, observed at g = 1.78, was 0.30 s. (iv) The amplitudes of the reversible g = 2.0026 radical observed at 19 K and the 1.2 ms optical 698 nm transient observed at 298 K were diminished to the same extent when treated with 1% LDS at room temperature for periods of 1 and 45 min. We interpret the strict correlation between the properties and lifetimes of the optical P-700+ A2 reaction pair and the ESR P-700+ center X- reaction pair to indicate that signal A2 and center X represent the same iron-sulfur center in Photosystem I.
mesh_terms: D002734:Chlorophyll / Q000378:metabolism*; D002736:Chloroplasts / Q000187:drug effects / Q000378:metabolism; D004578:Electron Spin Resonance Spectroscopy / Q000379:methods; D007700:Kinetics; D045342:Light-Harvesting Protein Complexes; D046911:Macromolecular Substances; D008872:Microwaves; D010084:Oxidation-Reduction; D045322:Photosynthetic Reaction Center Complex Proteins; D045331:Photosystem I Protein Complex; D010940:Plant Proteins / Q000378:metabolism*; D012967:Sodium Dodecyl Sulfate / Q000494:pharmacology; D013501:Surface-Active Agents / Q000494:pharmacology
chemical_list: D045342:Light-Harvesting Protein Complexes; D046911:Macromolecular Substances; D045322:Photosynthetic Reaction Center Complex Proteins; D045331:Photosystem I Protein Complex; D010940:Plant Proteins; D013501:Surface-Active Agents; D002734:Chlorophyll; D012967:Sodium Dodecyl Sulfate; C028913:dodecyl sulfate