The preparation and characterization of different types of light-harvesting pigment-protein complexes from some purple bacteria

Abstract

A general strategy, with some specific examples, is given for the isolation and purification of detergent-soluble, antenna pigment-protein complexes from the photosynthetic membranes. Absorption, fluorescence and circular dichroism spectra, and the pigment and protein composition of B800-B850-protein and B890-protein complexes of some purple bacteria (Rhodospirillum rubrum, Rhodopseudomonas sphaeroides and Rps. capsulata and Chromatium vinosum) are discussed. We conclude that there are probably two major classes of antenna carotenochlorophyll-proteins in purple bacteria containing bacteriochlorophyll a: a B890 complex which has one carotenoid and two bacteriochlorophyll molecules in the minimal unit (probable molecular weight around 20,000), and a B800 + B850 complex which has one carotenoid and three bacteriochlorophyll molecules in a similar-sized minimal unit. The whole cell spectrum of any purple bacterium can be reconstituted by combining different proportions of the spectra of these two complexes with that of the photochemical reaction centre.