Spectral hole burning of the primary electron donor state of Photosystem I

Abstract

Persistent photochemical hole burned profiles are reported for the primary electron donor state P700 of the reaction center of PS I. The hole profiles at 1.6 K for a wide range of burn wavelengths (λB) are broad (FWHM∼310 cm(-1)) and for the 45:1 enriched particles studied exhibit no sharp zero-phonon hole feature coincident with λB. The λB hole profiles are analyzed using the theory of Hayes et al. [J Phys Chem 1986, 90: 4928] for hole burning in the presence of arbitrarily strong linear electron-phonon coupling. A Huang-Rhys factor S in the range 4-6 and a corresponding mean phonon frequency in the range 35-50 cm(-1) together with an inhomogeneous line broadening of∼100 cm(-1) are found to provide good agreement with experiment. The zero-point level of P700(*) is predicted to lie at∼710 nm at 1.6K with an absorption maximum at∼702 nm. The hole spectra are discussed in the context of the hole spectra for the primary electron donor states of PS II and purple bacteria.

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

“…4 In the case of isolated LHCI the absorption band of the corresponding red Chls was estimated to be around 711 nm. 19 The Stokes shift of "normal" Chls (bulk Chls in photosystems) is only about 1-4 nm 21,22 (also our own unpublished results), much smaller than those observed for the red Chls. This difference was explained by strong pigment-pigment interactions and a mixing of the excited state with a charge transfer state in the case of red Chls.…”

Species-specific Differences of the Spectroscopic Properties of P700

“…2A we plotted the spectrum, shifted to the red by 28 nm to align the peak with the one of the ( 3 P700 -P700) spectrum from spinach. It should be noted that the large line width of the Q y band of the monomeric Chl a, which is bleached upon triplet formation, is mainly due to inhomogeneous broadening (31), whereas the low energy exciton band of P700 is predominantly homogeneously broadened (16,32). The T-S spectrum of Chl a completely lacks the second sharp negative and positive features at shorter wavelengths.…”

“…8) indicate that the low energy exciton band is very broad for all species even at low temperatures. A line width of 300 cm Ϫ1 at 5 K has been determined by hole-burning experiments using PS I complexes from spinach (32). The low energy exciton band of P700 is predominantly homogeneously broadened whereas the large line width of the Q y band of monomeric Chl a in micelles, which is bleached upon triplet formation, is mainly due to inhomogeneous broadening (31).…”

Fluorescence hole-burning and site-selective studies of LHCII

“…Very often, additional holes covering different regions of the absorption spectrum are observed. These additional holes may reveal: (1) coupling of the electronic transitions in the pigment molecules to the vibrations of the protein environment (called electronphonon coupling; Gillie et al 1989a, Pieper et al 1999, Hayes et al 2000, Ihalainen et al 2003, (2) coupling of the electronic transitions to the vibrations in the pigment molecules (Gillie et al 1989b), (3) existence of the excitonic coupling between different pigment molecules (Reddy et al 1994), (4) excitation energy transfer from the higher to the low energy states (red Chls; Hayes et al 2000, Zazubovich et al 2002, Ihalainen et al 2003. Furthermore, analysis of the AHB spectra gives insight into spectral characteristics of individual molecules and their distributions (homogeneous and inhomogeneous broadening) as well as into the excited state dynamics (Reddy et al 1994, Groot et al 1996, Pieper et al 1999, Dědic et al 2004.…”