Comparison of permeant ion uptake and carotenoid band shift as methods for determining the membrane potential in chromatophores from Rhodopseudomonas sphaeroides Ga

Biochem J. 1979 Apr 15;180(1):75-85. doi: 10.1042/bj1800075.


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.

Publication types

  • Comparative Study

MeSH terms

  • Antimycin A / pharmacology
  • Bacterial Chromatophores / physiology*
  • Carotenoids*
  • Membrane Potentials
  • NAD / metabolism
  • Rhodobacter sphaeroides / physiology*
  • Spectrophotometry
  • Succinates / metabolism
  • Thiocyanates / metabolism*


  • Succinates
  • Thiocyanates
  • NAD
  • Carotenoids
  • Antimycin A