title: Electrochromic responses of bacteriochlorophyll absorbance bands in purified light-harvesting complexes of Rhodobacter capsulatus reconstituted into liposomes.
abstract: Purified light harvesting complexes I and II (LHI and LHII) from Rhodobacter capsulatus were purified and separately incorporated into liposomes. Electrochromic absorbance changes of bacteriochlorophyll bands in the proteoliposomes in response to K(+)-diffusion potentials were recorded. In LHII proteoliposomes the application of positive-inside potentials led to red shifts in the bacteriochlorophyll absorbance bands centered at 377, 801 and 858 nm. Negative-inside potentials caused blue shifts of these bands. Electrochromism of the 590 nm band was too small to detect. The band at 858 nm was considerably more electrochromic than that at 801 nm. Electrochromic absorbance changes measured at 865-850 nm were linear with the applied diffusion potential. In LHI proteoliposomes positive-inside diffusion potentials caused red shifts of the bands centred at 374 nm and 880 nm. At 880 nm the response was linear with the applied diffusion potential and was equivalent in amplitude to that of the 858 nm band in LHII proteoliposomes. If it is assumed that the permanent dipole moment differences between the ground state and excited state of B800, B850 and B870 are similar and that polarisability effects are negligible, it follows that (a) the plane of the bacteriochlorin ring of B850 is more perpendicular to the membrane plane than that of B800 and (b) the orientations of B850 and B870 relative to the membrane plane are similar.
authors.affiliation: School of Biochemistry, University of Birmingham, UK.
authors.forename: J B
authors.initials: JB
authors.lastname: Jackson
authors.forename: M G
authors.initials: MG
authors.lastname: Goodwin
mesh_terms: D001426:Bacterial Proteins / Q000737:chemistry*; D001429:Bacteriochlorophylls / Q000032:analysis*; D004574:Electromagnetic Fields; D045342:Light-Harvesting Protein Complexes; D008081:Liposomes / Q000737:chemistry; D045332:Photosystem II Protein Complex; D010860:Pigments, Biological / Q000737:chemistry*; D011510:Proteolipids / Q000737:chemistry; D016354:Rhodobacter capsulatus / Q000737:chemistry*
chemical_list: D001426:Bacterial Proteins; D001429:Bacteriochlorophylls; D045342:Light-Harvesting Protein Complexes; D008081:Liposomes; D045332:Photosystem II Protein Complex; D010860:Pigments, Biological; D011510:Proteolipids; C023693:protein complex B800-850, Rhodobacter