The contribution of the carotenoid to the visible circular dichroism of the light-harvesting antenna of Rhodospirillum rubrum.
The visible c.d. spectrum of wild-type Rhodospirillum rubrum shows positive bands [Dratz, Schultz & Sauer (1966) Brookhaven Symp. Biol. 19, 303-318] that are largely due to the B880 antenna pigments, bacteriochlorophyll a and carotenoids. The bacteriochlorophyll c.d. band was absent from the spectrum of R. rubrum G9, a mutant unable to synthesize coloured carotenoids, and could be partly restored by adding extracted carotenoids to freeze-dried membrane vesicles isolated from that mutant. Therefore it seems to arise from either bacteriochlorophyll-carotenoid interactions or bacteriochlorophyll-protein interactions that are induced by the carotenoid. The more complex carotenoid c.d. band had different shapes in native and reconstituted carotenoid-containing membranes. Such differences suggest that the optical activity of the carotenoid in the B880 antenna arises from both non-degenerate and degenerate interactions.
Lozano
R M
RM
Centro de Investigaciones Biológicas del C.S.I.C., Madrid, Spain.
Fernández-Cabrera
C
C
Ramírez
J M
JM
D001429:Bacteriochlorophylls; D002338:Carotenoids; D002734:Chlorophyll / Q000031:analogs & derivatives; D002942:Circular Dichroism; D009154:Mutation; D012247:Rhodospirillum rubrum / Q000032:analysis* / Q000235:genetics; D013053:Spectrophotometry; D013057:Spectrum Analysis
D001429:Bacteriochlorophylls; D002734:Chlorophyll; D002338:Carotenoids