Carotenoid Shift Research Articles

Energy conversion-linked changes of carotenoid absorbance in Rhodospirillum rubrum chromatophores

In a study of the dark reactions of energy conversion in chromatophores from Rhodospirillum rubrum both ATP and inorganic pyrophosphate (PP i) have earlier been found by us to serve as energy donors for “reversed” energy transfer and electron transport causing reversible changes in the redox-state of endogenous cytochromes. Concomitant with these reactions there was found to occur a reversible shift in carotenoid absorbance. This shift is energy dependent in a very similar way as the cytochrome reactions as judged from results obtained with uncoupling agents and inhibitors of electron transport coupled energy transfer. With respect to both direction and extent, the ATP- or PP i-induced shift in carotenoid absorbance resembles the light-induced shift, which, however, occurs at a more than 10 5 times faster rate. On the other hand, the kinetics for the PP i-induced carotenoid shift has been found to resemble the kinetics of the PP i-induced reduction of endogenous b-type cytochrome. On the basis of these characteristics of the carotenoid responses, as compared to those of endogenous cytochrome, a metabolic link between an energy-rich intermediate of the electron transport coupled energy transfer pathway is postulated to exist and a scheme for the suggested connections between energy sources, chlorophyll, and cytochromes in relation to carotenoid is given.