title: Role for bound water and CH-pi aromatic interactions in photosynthetic electron transfer.
abstract: Photosystem I (PSI) is one of two photosynthetic reaction centers present in plants, algae, and cyanobacteria and catalyzes the reduction of ferredoxin and the oxidation of cytochrome c or plastocyanin. The PSI primary chlorophyll donor, which is oxidized in the primary electron-transfer events, is a heterodimer of chl a and a' called P700. It has been suggested that protein relaxation accompanies light-induced electron transfer in this reaction center (Dashdorj, N.; Xu, W.; Martinsson, P.; Chitnis, P. R.; Savikhin, S. Biophys. J. 2004, 86, 3121. Kim, S.; Sacksteder, C. A.; Bixby, K. A.; Barry, B. A. Biochemistry 2001, 40, 15384). To investigate the details of electron transfer and relaxation events in PSI, we have employed several experimental approaches. First, we report a pH-dependent viscosity effect on P700+ reduction; this result suggests a role for proton transfer in the PSI electron-transfer reactions. Second, we find that changes in hydration alter the rate of P700+ reduction and the interactions of P700 with the protein environment. This result suggests a role for bound water in electron transfer to P700+. Third, we present evidence that deuteration of the tyrosine aromatic side chain perturbs the vibrational spectrum, associated with P700+ reduction. We attribute this result to a linkage between CH-pi interactions and electron transfer to P700+.
authors.affiliation: Department of Biochemistry, Molecular Biology, and Biophysics, University of Minnesota, St. Paul, Minnesota 55108, USA.
authors.forename: Colette A
authors.initials: CA
authors.lastname: Sacksteder
authors.forename: Shana L
authors.initials: SL
authors.lastname: Bender
authors.forename: Bridgette A
authors.initials: BA
authors.lastname: Barry
mesh_terms: D002734:Chlorophyll / Q000031:analogs & derivatives* / Q000737:chemistry / Q000378:metabolism; D000077194:Chlorophyll A; D003903:Deuterium; D004578:Electron Spin Resonance Spectroscopy; D007700:Kinetics; D008958:Models, Molecular; D010084:Oxidation-Reduction; D045331:Photosystem I Protein Complex / Q000737:chemistry* / Q000378:metabolism; D017550:Spectroscopy, Fourier Transform Infrared; D046939:Synechocystis / Q000737:chemistry / Q000378:metabolism; D014443:Tyrosine / Q000737:chemistry / Q000378:metabolism; D014783:Viscosity; D014867:Water / Q000737:chemistry* / Q000378:metabolism
chemical_list: D045331:Photosystem I Protein Complex; D014867:Water; D002734:Chlorophyll; C085815:chlorophyll a'; D014443:Tyrosine; D003903:Deuterium; D000077194:Chlorophyll A