title: The low-energy forms of photosystem I light-harvesting complexes: spectroscopic properties and pigment-pigment interaction characteristics.
abstract: In this work the spectroscopic properties of the special low-energy absorption bands of the outer antenna complexes of higher plant Photosystem I have been investigated by means of low-temperature absorption, fluorescence, and fluorescence line-narrowing experiments. It was found that the red-most absorption bands of Lhca3, Lhca4, and Lhca1-4 peak, respectively, at 704, 708, and 709 nm and are responsible for 725-, 733-, and 732-nm fluorescence emission bands. These bands are more red shifted compared to "normal" chlorophyll a (Chl a) bands present in light-harvesting complexes. The low-energy forms are characterized by a very large bandwidth (400-450 cm(-1)), which is the result of both large homogeneous and inhomogeneous broadening. The observed optical reorganization energy is untypical for Chl a and resembles more that of BChl a antenna systems. The large broadening and the changes in optical reorganization energy are explained by a mixing of an Lhca excitonic state with a charge transfer state. Such a charge transfer state can be stabilized by the polar residues around Chl 1025. It is shown that the optical reorganization energy is changing through the inhomogeneous distribution of the red-most absorption band, with the pigments contributing to the red part of the distribution showing higher values. A second red emission form in Lhca4 was detected at 705 nm and originates from a broad absorption band peaking at 690 nm. This fluorescence emission is present also in the Lhca4-N-47H mutant, which lacks the 733-nm emission band.
authors.affiliation: Department of Biophysical Chemistry, Groningen Bimolecular Sciences and Biotechnology Institute, University of Groningen, Groningen, The Netherlands. R.Croce@rug.nl
authors.forename: Roberta
authors.initials: R
authors.lastname: Croce
authors.forename: Agnieszka
authors.initials: A
authors.lastname: Chojnicka
authors.forename: Tomas
authors.initials: T
authors.lastname: Morosinotto
authors.forename: Janne A
authors.initials: JA
authors.lastname: Ihalainen
authors.forename: Frank
authors.initials: F
authors.lastname: van Mourik
authors.forename: Jan P
authors.initials: JP
authors.lastname: Dekker
authors.forename: Roberto
authors.initials: R
authors.lastname: Bassi
authors.forename: Rienk
authors.initials: R
authors.lastname: van Grondelle
mesh_terms: D000042:Absorption; D016880:Anisotropy; D001703:Biophysics / Q000379:methods*; D045342:Light-Harvesting Protein Complexes / Q000737:chemistry*; D009154:Mutation; D016011:Normal Distribution; D045331:Photosystem I Protein Complex / Q000737:chemistry*; D010858:Pigmentation; D010940:Plant Proteins / Q000378:metabolism; D013050:Spectrometry, Fluorescence; D013053:Spectrophotometry / Q000379:methods; D013696:Temperature
chemical_list: D045342:Light-Harvesting Protein Complexes; D045331:Photosystem I Protein Complex; D010940:Plant Proteins