| Abstract
| - In the LH2 proteins from Rhodobacter (Rb.) sphaeroides, the hydrogen bonds between thebacteriochlorophyll (Bchl) molecules and their proteic binding sites exhibit a strong variance with respectto carotenoid content and type. In the absence of the carotenoid molecule, such as in the LH2 from Rb.sphaeroides R26.1, the void in the protein structure induces a significant reorganization of the bindingsite of both Bchl molecules responsible for the 850 nm absorption, which is not observed when the 800nm absorbing Bchl is selectively removed from these complexes. FT Raman spectra of LH2 complexesfrom Rb. sphaeroides show that the strength of the hydrogen bond between the 850 nm absorbing Bchlbound to the α polypeptide and the tyrosine α45 depends precisely on the chemical nature of the boundcarotenoid. These results suggest that the variable extremity of the carotenoid is embedded in these LH2complexes, lying close to the interacting Bchl molecules. In the LH2 from Rhodopseudomonas acidophila,the equivalent part of the rhodopin glucoside, which bears the glucose group, lies close to the aminoterminal of the antenna polypeptide. This contrast suggests that the structure of the carotenoid bindingsite in LH2 complexes strongly depends on the bacterial species and/or on the chemical nature of thebound carotenoid.
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