title: High-pressure and stark hole-burning studies of chlorosome antennas from Chlorobium tepidum.
abstract: Results from high-pressure and Stark hole-burning experiments on isolated chlorosomes from the green sulfur bacterium Chlorobium tepidum are presented, as well as Stark hole-burning data for bacteriochlorophyll c (BChl c) monomers in a poly(vinyl butyral) copolymer film. Large linear pressure shift rates of -0.44 and -0.54 cm(-1)/MPa were observed for the chlorosome BChl c Q(y)-band at 100 K and the lowest Q(y)-exciton level at 12 K, respectively. It is argued that approximately half of the latter shift rate is due to electron exchange coupling between BChl c molecules. The similarity between the above shift rates and those observed for the B875 and B850 BChl a rings of the light-harvesting complexes of purple bacteria is emphasized. For BChl c monomer, fDeltamu++ = 0.35 D, where Deltamu+ is the dipole moment change for the Q(y) transition and f is the local field correction factor. The data establish that Deltamu+ is dominated by the matrix-induced contribution. The change in polarizability (Deltaalpha) for the Q(y) transition of the BChl c monomer is estimated at 19 A(3), which is essentially identical to that of the Chl a monomer. Interestingly, no Stark effects were observed for the lowest exciton level of the chlorosomes (maximum Stark field of 10(5) V/cm). Possible explanations for this are given, and these include consideration of structural models for the chlorosome BChl c aggregates.
authors.affiliation: Department of Chemistry and Biochemistry, Arizona State University, Tempe, Arizona 85287, USA.
authors.forename: H M
authors.initials: HM
authors.lastname: Wu
authors.forename: M
authors.initials: M
authors.lastname: Rätsep
authors.forename: C S
authors.initials: CS
authors.lastname: Young
authors.forename: R
authors.initials: R
authors.lastname: Jankowiak
authors.forename: R E
authors.initials: RE
authors.lastname: Blankenship
authors.forename: G J
authors.initials: GJ
authors.lastname: Small
mesh_terms: D001426:Bacterial Proteins / Q000737:chemistry; D001429:Bacteriochlorophylls; D019414:Chlorobi / Q000502:physiology*; D045342:Light-Harvesting Protein Complexes; D015388:Organelles / Q000502:physiology*; D045322:Photosynthetic Reaction Center Complex Proteins / Q000737:chemistry* / Q000378:metabolism; D011145:Polyvinyls; D011312:Pressure; D013053:Spectrophotometry
chemical_list: D001426:Bacterial Proteins; D001429:Bacteriochlorophylls; D045342:Light-Harvesting Protein Complexes; D045322:Photosynthetic Reaction Center Complex Proteins; D011145:Polyvinyls; C002084:bacteriochlorophyll c; C027464:polyvinylbutyral