title: The carotenoid band shift in reaction centers from from Rhodopseudomonas sphaeroides.
abstract: A specific carotenoid associated with reaction centers purified from Rhodopseudomonas sphaeroides shows an optical absorbance change in response to photochemical activity, at temperatures down to 35 K. The change corresponds to a bathochromic shift of 1 nm of each absorption band. The same change is induced by either chemical oxidation or photo-oxidation of reaction center bacteriochlorophyll (P-870). Reduction of the electron acceptor of the reaction center, either chemically or photochemically, does not cause a carotenoid absorbance change or modify a change already induced by oxidation of P-870. The change of the carotenoid spectrum can therefore be correlated with the appearance of positive charge in the reaction center. In these studies we observed that at 35 K the absorption band of reaction center bacteriochlorophyll near 600 nm exhibits a shoulder at 605 nm. The resolution into two components is more pronounced in the light-dark difference spectrum. This observation is consistent with our earlier finding, that the "special pair" of bacteriochlorophyll molecules that acts as photochemical electron donor has a dimer-like absorption spectrum in the near infrared.
mesh_terms: D001429:Bacteriochlorophylls / Q000378:metabolism; D002338:Carotenoids / Q000378:metabolism; D010084:Oxidation-Reduction; D010777:Photochemistry; D012242:Rhodobacter sphaeroides / Q000378:metabolism*; D013057:Spectrum Analysis; D013696:Temperature
chemical_list: D001429:Bacteriochlorophylls; D002338:Carotenoids