title: The carotenoid shift in Rhodopseudomonas sphaeroides. Change induced under continuous illumination.
abstract: The spectrum of the carotenoid shift generated under continuous illumination in the GIC mutant of Rhodopseudomonas sphaeroides, which has a single carotenoid, has been examined under a variety of conditions expected to alter the size of the membrane potential. If the difference spectrum observed was due to a species with the spectrum of the bulk pigment, it would correspond to a change of a variable proportion of the pigment to a form absorbing at a higher wavelength. The maximal change induced by light could be described as a shift of about 10% of the pigment by 7 nm to the red, assuming that the shifted species was spectrally identical to the bulk carotenoid. It is concluded that the changes seen are not easily compatible with a progressive red shift in the whole spectrum with increasing applied potential as would be expected from a simple linear electrochromic mechanism; alternative hypotheses are discussed.
mesh_terms: D020130:Bacterial Chromatophores / Q000528:radiation effects*; D002338:Carotenoids / Q000528:radiation effects*; D008027:Light; D009154:Mutation; D012242:Rhodobacter sphaeroides; D013053:Spectrophotometry
chemical_list: D002338:Carotenoids