title: Universality of energy and electron transfer processes in photosystem I.
abstract: Femtosecond transient absorption spectroscopy has been used to investigate the photoinduced energy and electron transfer processes in photosystem I (PS I) particles from cyanobacteria, green algae, and higher plants. At room temperature, the kinetics observed in all three species are very similar: Following 590 nm excitation, an equilibration process(es) with a 3.7-7.5 ps lifetime was observed, followed by a 19-24 ps process that is associated with trapping. In all three species long-wavelength pigments (pigments that absorb at longer wavelengths than the primary electron donor) were observed. The difference spectrum associated with reduction of the primary electron acceptor [Ao(-)-Ao) difference spectrum] was obtained for all three species. The (Ao(-)-Ao) difference spectra obtained from measurements using detergent-isolated PS I particles from spinach and Chlamydomonas reinhardtii are similar but clearly membrane fragments. In all three species the reduced primary electron acceptor (Ao(-)) is reoxidized extremely rapidly, in about 20 ps. The difference spectrum associated with Ao reduction appears to contain contributions from more than a single chlorophyll pigment.
mesh_terms: D000818:Animals; D016825:Chlamydomonas reinhardtii / Q000378:metabolism; D000458:Cyanobacteria / Q000378:metabolism; D004579:Electron Transport; D004734:Energy Metabolism; D007700:Kinetics; D045342:Light-Harvesting Protein Complexes; D045322:Photosynthetic Reaction Center Complex Proteins / Q000378:metabolism*; D045331:Photosystem I Protein Complex; D018724:Spinacia oleracea / Q000378:metabolism
chemical_list: D045342:Light-Harvesting Protein Complexes; D045322:Photosynthetic Reaction Center Complex Proteins; D045331:Photosystem I Protein Complex