The Soret absorption properties of carotenoids and chlorophylls in antennacomplexes of higher plants

The absorption spectra of two light harvesting complexes from higher plants , CP29 and LHC II, have been analysed in the Soret region in order to obtai n a description in terms of the absorption spectra of the individual pigmen ts. This information is of great practical use when applying spectroscopic techniques to the study of energy transfer in photosynthesis such as time-r esolved spectroscopy thus allowing determination of the relative absorption cross-section for the different chromophores in the system as a function o f wavelength. In this study, recombinant Lhc proteins carrying point mutati ons in pigment-binding residues have been used in order to obtain the spect ral shape of individual chromophores by differential spectroscopy with resp ect to the WT protein. Combinations of spectra thus obtained were then used to fit the absorption spectra of WT and mutant pigment-proteins according to the constraints posed by stoichiometry of pigments as derived by biochem ical analysis. This procedure allowed identification of each pigment in ter m of its wavelength position, spectral shape and extinction coefficient. Th e data obtained by this procedure have been successfully applied to the des cription of other higher plant Lhc proteins thus supporting the view that t he Lhc superfamily members share specific pigment-protein interactions as s uggested by sequence homology.