title: Identification of the upper exciton component of the B850 bacteriochlorophylls of the LH2 antenna complex, using a B800-free mutant of Rhodobacter sphaeroides.
abstract: In this paper, we report the circular dichroism (CD) spectra of two types of LH2-only mutants of Rhodobacter sphaeroides. In the first, only the wild type LH2 is present, while i the second, the B800 binding site of LH2 has been either destabilized or removed. For the first time, we have identified a band in the CD spectrum of LH2, located at approximately 780 nm, that can be ascribed to the high exciton component of the B850 band. The experimental spectra have been modeled by theoretical calculations. On this basis, the average interaction strength between the monomers in the B850 ring can be estimated to be approximately 300 cm-1. In addition, we suggest that in LH2 of Rb. sphaeroides the angles made by the Qy transitions of the B850 BChls with respect to the plane of the ring are slightly different from those calculated from the crystal structure of the Rhodopseudomonas acidophila LH2 complex.
authors.affiliation: Department of Physical and Theoretical Chemistry, Vrije Universiteit, Amsterdam, The Netherlands.
authors.forename: M H
authors.initials: MH
authors.lastname: Koolhaus
authors.forename: R N
authors.initials: RN
authors.lastname: Frese
authors.forename: G J
authors.initials: GJ
authors.lastname: Fowler
authors.forename: T S
authors.initials: TS
authors.lastname: Bibby
authors.forename: S
authors.initials: S
authors.lastname: Georgakopoulou
authors.forename: G
authors.initials: G
authors.lastname: van der Zwan
authors.forename: C N
authors.initials: CN
authors.lastname: Hunter
authors.forename: R
authors.initials: R
authors.lastname: van Grondelle
mesh_terms: D001429:Bacteriochlorophylls / Q000737:chemistry*; D002942:Circular Dichroism; D045342:Light-Harvesting Protein Complexes; D016296:Mutagenesis; D045322:Photosynthetic Reaction Center Complex Proteins / Q000737:chemistry* / Q000235:genetics; D012242:Rhodobacter sphaeroides / Q000737:chemistry* / Q000235:genetics
chemical_list: D001429:Bacteriochlorophylls; D045342:Light-Harvesting Protein Complexes; D045322:Photosynthetic Reaction Center Complex Proteins