title: Functions of carotenoids in xanthorhodopsin and archaerhodopsin, from action spectra of photoinhibition of cell respiration.
abstract: The recent discovery of a carotenoid light-harvesting antenna in xanthorhodopsin, a retinal-based proton pump in Salinibacter ruber, made use of photoinhibition of respiration in whole cells to obtain action spectra [Balashov et al. Science 309, (2005) 2061-2064]. Here we provide further details of this phenomenon, and compare action spectra in three different systems where carotenoids have different functions or efficiencies of light-harvesting. The kinetics of light-induced inhibition of respiration in Salinibacter ruber was determined with single short flashes, and the photochemical cross section of the photoreaction was estimated. These measurements confirm that the xanthorhodopsin complex includes no more than a few, and most likely only one, carotenoid molecule, which is far less than the core complex antenna of photosynthetic bacteria. Although the total cross-section of light absorption in the purple bacterium Rhodospirillum rubrum greatly exceeds that in Salinibacter, the cross-sections are roughly equivalent in the shared wavelength range. We show further that despite interaction of bacterioruberin with archaerhodopsin, another retinal-based proton pump, there is no significant energy transfer from this carotenoid. This emphasizes the uniqueness of the salinixanthin-retinal interaction in xanthorhodopsin, and indicates that bacterioruberin in Halorubrum species has a structural or photoprotective rather than energetic role.
authors.affiliation: Institute of Basic Biological Problems, Russian Academy of Sciences, Pushchino 142290, Russia.
authors.forename: Vladimir A
authors.initials: VA
authors.lastname: Boichenko
authors.forename: Jennifer M
authors.initials: JM
authors.lastname: Wang
authors.forename: Josefa
authors.initials: J
authors.lastname: Antón
authors.forename: Janos K
authors.initials: JK
authors.lastname: Lanyi
authors.forename: Sergei P
authors.initials: SP
authors.lastname: Balashov
mesh_terms: D019843:Archaeal Proteins / Q000737:chemistry* / Q000378:metabolism / Q000528:radiation effects; D001426:Bacterial Proteins / Q000737:chemistry / Q000378:metabolism / Q000528:radiation effects; D041963:Bacteroidetes / Q000378:metabolism / Q000528:radiation effects; D002338:Carotenoids / Q000737:chemistry* / Q000378:metabolism / Q000528:radiation effects; D004735:Energy Transfer; D006216:Halobacteriaceae / Q000378:metabolism / Q000528:radiation effects; D018462:Photobiology; D010777:Photochemistry; D012243:Rhodopsin / Q000737:chemistry* / Q000378:metabolism / Q000528:radiation effects; D012247:Rhodospirillum rubrum / Q000378:metabolism / Q000528:radiation effects; D013053:Spectrophotometry; D017494:Proton Pumps
chemical_list: D019843:Archaeal Proteins; D001426:Bacterial Proteins; D002338:Carotenoids; D012243:Rhodopsin; C055476:archaerhodopsin protein, Archaea; D017494:Proton Pumps