Rhodobacter sphaeroides with spheroidene

The polyene chain of the carotenoid predominantly interacts with aromatic and hydro-phobic amino acids, like it is seen for spheroidene in the reaction center of Rhodobacter sphaeroides (Ermles et al., 1994). Similarly, in the major LHCll of higher plants, the superhelix formed by the transmembrane ahelices A and B seems to be stabilized by two carotenoid molecules bound into the grooves of the superhelix (Kiihlbrandt et al, 1994). Hydrophobic interactions with these carotenoids may be an essential factor for stablizing the arrangement of a helices in this complex, as there are relatively few ionic helix-helix interactions in the major LHCll as compared to other complexes like bacterio-rhodopsin or the bacterial reaction center. 

Triplet energy transfer between the primary donorand carotenoids in Rhodobacter sphaeroides R-26.1 reaction centers incorporated with spheroidene analogs havi ng different extents of ff-electron conjugation. Photochem Photobiol 66 97-104 Feher G and Okamura Y (1978) Chemical composition and properties of reaction centers. In Clayton RK and Sistrom WR (eds) The Photosynthetic Bacteria, pp 349-386. Plenum Press, New Y ork... 

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