LIGHT-INDUCED INHIBITION OF RESPIRATION AND ORGANIZATION OF PHOTOSYNTHETIC UNITS IN WHOLE CELLS OF PURPLE BACTERIA

The structural and functional organization of photosynthetic units in various species of nonsulfur purple bacteria was studied using the act ion spectra and effective cross-sections of absorption for light-induc ed inhibition of respiration in whole cells. in Rhodospirillum rubrum, which contains a complex of reaction center (RC) with B875, and Rhodo bacter capsulatus, which contains RC complexes with B875 and B800-850 have functional photosynthetic units sizes of 27 +/- 4 and 53 +/- 6 ba cteriochlorophyll molecules, respectively. The cells of Rhodopseudomon as palustris AB grown under high-light and low-light conditions displa yed different action spectra and functional antenna sizes of 44 +/- 4 and 112 +/- 13 molecules of bacteriochlorophyll, respectively. This ph enomenon indicates that adaptive changes occurred in the pigment compo sition of the complex B800-850 and its stoichiometry with RCs. However , there was no considerable change in the effective absorption cross-s ection for light-induced inhibition of respiration in Rps. palustris u nder constant illumination that closed 50-70% of RCs or after treatmen ts inducing Mg2+-dependent changes in cooperativity and/or protein pho sphorylation in photosynthetic units. Concerning their function, this means that the multicenter organization of photosynthetic units in pur ple bacteria offers no substantial advantage over the unicentral organ ization in terms of the effectiveness of conversion of the energy of l ight.