Flash-Induced Electrochromic Band Shifts, is It a Simple Mechanism?

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Abstract
The flash-induced carotenoid bandshifts have been studied for various strains of both Rho-dopseudomonas sphaeroides and capsulata. A technique for calculating shifts of isobestic points down to 0.05 nm is described. To this end, special attention has been paid to the appropriate correction for reaction center absorbance changes occuring concommitantly with the carotenoid bandshifts. Plots of the wavelength of the isobestic point versus the corresponding absorption changes at the maximum of the difference spectrum have been made, suggesting the existence of different pools of carotenoids. The various pools of carotenoids seem to have different sizes, inducing non-linearities in the plots. In some cases spectral differences of the pools have to be assumed. A possible interpretation of the results would be that each electrogenic span of the electron transport chain is to be associated with its own pool of carotenoids, all the pools behaving in somewhat independant way. We discuss possible difficulties in making those measurements.

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