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

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 (_B) are broad (FWHM310 cm^-1) and for the 45:1 enriched particles studied exhibit no sharp zero-phonon hole feature coincident with _B. The _B 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 of100 cm^-1 are found to provide good agreement with experiment. The zero-point level of P700^* is predicted to lie at710 nm at 1.6K with an absorption maximum at702 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.Abbreviations NPHB nonphotochemical hole burning - O.D. optical density - PSBH phonon sideband hole - PS I Photosystem I P680 - P700, P870, P960 the primary electron donors of Photosystem II, Photosystem I, Rhodobacter sphaeroides, Rhodopseudomonas viridis - PED primary electron donor - RC reaction center - ZPH zero-phonon holes