title: Comparison of permeant ion uptake and carotenoid band shift as methods for determining the membrane potential in chromatophores from Rhodopseudomonas sphaeroides Ga.
abstract: 1. A comparison was made of two methods for estimating the membrane potential in chromatophores from Rhodopseudomonas sphaeroides Ga. Illuminated chromatophores generated a potential that is apparently much larger when estimated on the basis of the red-band shift of carotenoids rather than from the extent of uptake of the permeant SCN- ion. 2. In contrast, when the chromatophores were oxidizing NADH or succinate the uptake of SCN- indicated a larger membrane potential than was estimated from the carotenoid band shift. 3. The extent of SCN- uptake and the carotenoid-band shift respond differently to changes in the ionic composition of the reaction medium. 4. The effects of antimycin on the carotenoid band shift and SCN- uptake are reported. 5. It is concluded that the carotenoid band shift and the uptake of SCN- are responding to different aspects of the energized state.
mesh_terms: D000968:Antimycin A / Q000494:pharmacology; D020130:Bacterial Chromatophores / Q000502:physiology*; D002338:Carotenoids; D008564:Membrane Potentials; D009243:NAD / Q000378:metabolism; D012242:Rhodobacter sphaeroides / Q000502:physiology*; D013053:Spectrophotometry; D013386:Succinates / Q000378:metabolism; D013861:Thiocyanates / Q000378:metabolism*
chemical_list: D013386:Succinates; D013861:Thiocyanates; D009243:NAD; D002338:Carotenoids; D000968:Antimycin A