Article Information

• PDF (1848 kb)

PubMed

• Articles by G. Trinkunas
• Articles by A.R. Holzwarth

Related Articles

• Ultrafast Primary Processes in Photosystem I of the Cyanobac...

  Ultrafast Primary Processes in Photosystem I of the Cyanobacterium Synechocystis sp. PCC 6803 Biophysical Journal, Volume 76, Issue 6, 1 June 1999, Pages 3278-3288 Sergei Savikhin, Wu Xu, Victor Soukoulis, Parag R. Chitnis and Walter S. Struve Abstract Ultrafast primary processes in the trimeric photosystem I core antenna-reaction center complex of the cyanobacterium sp. PCC 6803 have been examined in pump-probe experiments with ∼100fs resolution. A global analysis of two-color profiles, excited at 660nm and probed at 5nm intervals from 650 to 730nm, reveals 430fs kinetics for spectral equilibration among bulk antenna chlorophylls. At least two lifetime components (2.0 and 6.5ps in our analysis) are required to describe equilibration of bulk chlorophylls with far red-absorbing chlorophylls (>700nm). Trapping at P700 occurs with 24-ps kinetics. The multiphasic bulk ↔ red equilibration kinetics are intriguing, because prior steady-state spectral studies have suggested that the core antenna in sp. contains only one red-absorbing chlorophyll species (C708). The disperse kinetics may arise from inhomogeneous broadening in C708. The one-color optical anisotropy at 680nm (near the red edge of the bulk antenna) decays with 590fs kinetics; the corresponding anisotropy at 710nm shows ∼3.1ps kinetics. The latter may signal equilibration among symmetry-equivalent red chlorophylls, bound to different monomers within trimeric photosystem I. Abstract | Full Text | PDF (232 kb)

• Electrochromic Shift of Chlorophyll Absorption in Photosyste...

  Electrochromic Shift of Chlorophyll Absorption in Photosystem I from Synechocystis sp. PCC 6803: A Probe of Optical and Dielectric Properties around the Secondary Electron Acceptor Biophysical Journal, Volume 86, Issue 5, 1 May 2004, Pages 3121-3130 Naranbaatar Dashdorj, Wu Xu, Peter Martinsson, Parag R. Chitnis and Sergei Savikhin Abstract Nanosecond absorption dynamics at ∼685nm after excitation of photosystem I (PS I) from sp. PCC 6803 is consistent with electrochromic shift of absorption bands of the Chl pigments in the vicinity of the secondary electron acceptor A. Based on experimental optical data and structure-based simulations, the effective local dielectric constant has been estimated to be between 3 and 20, which suggests that electron transfer in PS I is accompanied by considerable protein relaxation. Similar effective dielectric constant values have been previously observed for the bacterial photosynthetic reaction center and indicate that protein reorganization leading to effective charge screening may be a necessary structural property of proteins that facilitate the charge transfer function. The data presented here also argue against attributing redmost absorption in PS I to closely spaced antenna chlorophylls (Chls) A38 and A39, and suggest that optical transitions of these Chls, along with that of connecting chlorophyll (A40) lie in the range 680–695nm. Abstract | Full Text | PDF (272 kb)

• Antenna structure and excitation dynamics in photosystem I. ...

  Antenna structure and excitation dynamics in photosystem I. II. Studies with mutants of Chlamydomonas reinhardtii lacking photosystem II Biophysical Journal, Volume 56, Issue 1, 1 July 1989, Pages 95-106 T.G. Owens, S.P. Webb, L. Mets, R.S. Alberte and G.R. Fleming Abstract Using time-resolved single photon counting, fluorescence decay in photosystem I (PS I) was analyzed in mutant strains of Chlamydomonas reinhardtii that lack photosystem II. Two strains are compared: one with a wild-type PS I core antenna (120 chlorophyll a/P700) and a second showing an apparent reduction in core antenna size (60 chlorophyll a/P700). These data were calculated from the lifetimes of core antenna excited states (75 and 45 ps, respectively) and from pigment stoichiometries. Fluorescence decay in wild type PS I is composed of two components: a fast 75-ps decay that represents the photochemically limited lifetime of excited states in the core antenna, and a minor (less than 10%) 300–800 ps component that has spectral characteristics of both peripheral and core antenna pigments. Temporal and spectral properties of the fast PS I decay indicate that (a) excitations are nearly equilibrated among the range of spectral forms present in the PS I core antenna, (b) an average excitation visits a representative distribution of core antenna spectral forms on all pigment-binding subunits regardless of the origin of the excitation, (c) reduction in core antenna size does not alter the range of antenna spectral forms present, and (d) transfer from peripheral antennae to the PS I core complex is rapid (less than 5 ps). Abstract | PDF (1364 kb)

• …more

Abstract

A procedure is described to generate and optimize the lattice models for spectrally inhomogeneous photosynthetic antenna/reaction center (RC) particles. It is based on the genetic algorithm search for the pigment spectral type distributions on the lattice by making use of steady-state and time-resolved spectroscopic input data. Upon a proper fitness definition, a family of excitation energy transfer models can be tested for their compatibility with the availability experimental data. For the case of the photosystem I core antenna (99 chlorophyll + primary electron donor pigment (P700)), three spectrally inhomogeneous three-dimensional lattice models, differing in their excitation transfer conditions, were tested. The relevant fit parameters were the pigment distribution on the lattice, the average lattice spacing of the main pool pigments, the distance of P700 and of long wavelength-absorbing (LWA) pigments to their nearest-neighbor main pool pigments, and the rate constant of charge separation from P700. For cyanobacterial PS I antenna/RC particles containing a substantial amount of LWA pigments, it is shown that the currently available experimental fluorescence data are consistent both with more migration-limited, and with more trap-limited excitation energy transfer models. A final decision between these different models requires more detailed experimental data. From all search runs about 30 different relative arrangements of P700 and LWA pigments were found. Several general features of all these different models can be noticed: 1) The reddest LWA pigment never appears next to P700. 2) The LWA pigments in most cases are spread on the surface of the lattice not far away from P700, with a pronounced tendency toward clustering of the LWA pigments. 3) The rate constant kP700 of charge separation is substantially higher than 1.2 ps-1, i.e., it exceeds the corresponding rate constant of purple bacterial RCs by at least a factor of four. 4) The excitation transfer within the main antenna pool is very rapid (less than 1 ps equilibration time), and only the equilibration with the LWA pigments is slow (about 10–12 ps). The conclusions from this extended study on three-dimensional lattices are in general agreement with the tendencies and limitations reported previously for a simpler two-dimensional array. Once more detailed experimental data are available, the procedure can be used to determine the relevant rate-limiting processes in the excitation transfer in such spectrally inhomogeneous antenna systems.