title: Binding of carotenoids on reaction centers from Rhodopseudomonas sphaeroides R 26.
abstract: The carotenoid-less reaction centers isolated from Rhodopseudomonas sphaeroides (strain R 26) bind pure all-trans spheroidene as well as spheroidenone in a nearly 1 : 1 molar ratio with respect to P-870. Neither beta-carotene nor spirilloxanthin, both absent from wild-type Rps. sphaeroides, could be bound in appreciable amounts. Resonance Raman spectra of the carotenoid-reaction center complex indicate that the carotenoid is bound as a cis isomer, its conformation being very close, although probably not identical, to that assumed by the carotenoid in the wild-type reaction centers. The electronic absorption spectra of the carotenoid-reaction center complexes are in good agreement with such a interpretation. When bound to the R 26 reaction centers, spheroidene displays light-induced absorbance changes identical in peak wavelengths and comparable in amplitudes to those observed in the wild-type reaction centers. Thus the binding of the carotenoid to the R 26 reaction centers most likely occurs at the same proteic site as in the wild-type reaction centers. This site shows selectivity towards the nature of carotenoids, and has the same sterical requirement as in the wild type, leading to the observed all-trans to cis isomerisation.
mesh_terms: D001426:Bacterial Proteins / Q000378:metabolism*; D001429:Bacteriochlorophylls / Q000378:metabolism; D002338:Carotenoids / Q000378:metabolism*; D003624:Darkness; D007700:Kinetics; D008027:Light; D045342:Light-Harvesting Protein Complexes; D010788:Photosynthesis; D045322:Photosynthetic Reaction Center Complex Proteins; D012242:Rhodobacter sphaeroides / Q000378:metabolism*; D013053:Spectrophotometry; D013059:Spectrum Analysis, Raman
chemical_list: D001426:Bacterial Proteins; D001429:Bacteriochlorophylls; D045342:Light-Harvesting Protein Complexes; D045322:Photosynthetic Reaction Center Complex Proteins; D002338:Carotenoids