The resonance Raman spectrum of carotenoids as an intrinsic probe for membrane potential. Oscillatory changes in the spectrum of neurosporene in the chromatophores of Rhodopseudomonas sphaeroides.

The resonance Raman spectrum of the carotenoid neurosporene is shown to be a sensitive monitor of absorption shifts, and thus changes in membrane potential, in chromatophores of the GlC mutant of Rhodopseudomonas sphaeroides. For a Raman excitation wavelength at 472.7 nm, the intensities of the two most prominent resonance Raman features (v1 and v2) respond very differently to small shifts in the absorption maxima. Thus, the ratio intensity v1/intensity v2 is a sensitive probe for absorption shifts. Changes in this ratio of approximately 20% were observed during a valinomycin induced diffusion potential. At 5 degrees C changes in the average intensity ratio of +6, -4 and -14% were brought about by oligomycin, FCCP and sodium deoxycholate, respectively. The changes in intensity ratio were temperature dependent and, in addition, effects due to the laser beam acting as an actinic light could be detected. Oscillatory changes were observed in absolute Raman and Rayleigh scattering intensities for chromatophores at 5 degrees C and for intact cells under growing conditions.