Correlation of membrane-potential-sensing carotenoid to pigment-protein complex II in Rhodopseudomonas sphaeroides.

The changes in carotenoid absorbance induced by illumination or by a diffusion potential were larger in chromatophores from cells cultured under low light intensity than those in chromatophores from high-light culture in a photosynthetic bacterium, Rhodopseudomonas sphaeroides. The carotenoid molecules which are associated with the pigment-protein complex (with the infrared bacteriochlorophyll peaks at 800 and 850 nm) (complex II) probably respond to the electrical field changes in the chromatophore membrane.