Simulations of the temperature dependence of energy transfer in the PSI core antenna

Abstract

In order to understand the organization of the PSI core antenna and to interpret results obtained from studies of the temperature and wavelength dependence of energy transfer and trapping in the PSI particles, we have constructed a model for PSI in which spectral heterogeneity is considered via a self-consistent approach based on Forster transport. The temperature dependence of the absorption and emission spectra of the individual Chl molecules in the protein matrix is calculated based on a model Hamiltonian which includes a phonon contribution. Time and wavelength resolved kinetics of PSI at different temperatures are investigated by means of two-dimensional lattice models. We conclude that wavelength-dependent fluorescence decay kinetics result only when two or more bottlenecks exist in the energy transfer and trapping process. A single trap or several pseudo-traps with spectrally identical environments do not lead to wavelength dependent decays. Simple funnel arrangements of the spectral types can be ruled out. At least one pigment with energy lower than the photochemical trap located close to the reaction center is required to produce the trends of the fluorescence lifetimes observed experimentally. The remainder of the core antenna is consistent with a random arrangement of spectral types.

Energy transfer and trapping in photosystem I reaction centers from cyanobacteria.

“…This model is consistent with the rather complex observed wavelength dependence of fluorescence decay in PSI at low temperatures (9). It was also concluded, based on the simulation, that red pigments are necessary to interpret the temperature and wavelength dependence of fluorescence decay at low temperatures (8,9). This conclusion is supported by the direct observation of red fluorescence (the fluorescence peaks to the red of 700 nm) of PSI at room temperature (10).…”

“…This conclusion is supported by the direct observation of red fluorescence (the fluorescence peaks to the red of 700 nm) of PSI at room temperature (10). One of the key assumptions in the simulations (8) is the average distance (11.5 A) between Chls, which is consistent with the x-ray structure (1). The simulation results indicated a nearly single exponential decay of the fluorescence at room temperature, implying that spectral equilibration occurs on a time scale faster than the trapping time.…”

“…To take account of inhomogeneous broadening and multiple spectral types in PSI, a multicolor random model with a few pigments that absorb above 700 nm (red pigments) was proposed (8). This model is consistent with the rather complex observed wavelength dependence of fluorescence decay in PSI at low temperatures (9).…”

Characterization of Low-Energy Chlorophylls in the PSI-LHCI Supercomplex from Chlamydomonas reinhardtii. A Site-Selective Fluorescence Study

“…The position and the oscillator strength of the former band indicate that it could be attributed to the primary donor, P. A similar band at 697 nm with the oscillator strength of ∼2 resulting from Gaussian decomposition was attributed to the primary donor in PSI from Synechocystis PCC 6803, 4 Synechocystis PCC 7942, 14 and C. reinhardtii. 28 The same position of the primary donor absorption in cyanobacteria and C. reinhardtii is intriguing because the (P + -P) difference spectrum from the latter species peaks consistently a few nanometers to the blue relative to cyanobacteria. 30,[39][40][41][42][43] A sharp band at 696 nm also was observed in PSI-LHCI from Arabidospsis and attributed to pigments in the interfaces between LHCI subunits or between LHCI and PSI.…”

“…44 We may speculate that the second pool, at 701 nm, correspond to one to two red Chls located close to the RC as reported for C. reinhardtii. 28,29 The sharp character of the 697-and 701-nm bands may indicate that the mechanism of their red shift is different from the C700 pool: for example that they originate from monomeric Chls which are tuned by the protein environment. 11 13 and Gobets and van Grondelle.…”