Binding of carotenoids on reaction centers from Rhodopseudomonas sphaeroides R 26 |
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Authors: | Ileana Agalidis Marc Lutz Francoise Reiss-Husson |
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Institution: | 1. Laboratoire de Photosynthèse, C.N.R.S., 91190 Gif-sur-Yvette France;2. Service de Biophysique, Département de Biologie, Centre d''Etudes Nucléaires de Saclay, B.P. 2, 91190 Gif-sur-Yvette France |
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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 β-carotene nor spirilloxanthin, both absent from wild-type Rps. sphaeroides, could be bound in appreciable amounts. Resonance Raman spectra of the carotenoidreaction 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. |
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Keywords: | Reaction center Carotenoid Bacterial photosynthesis Raman spectroscopy (Rps sphaeroides) BChl Bacteriochlorophyll |
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