Effect of low pH values on chromatophores, core complexes, and peripheral light harvesting complexes isolated from the sulfur bacterium Allochromatium minutissimum

Abstract

Spectral methods have been used to trace pheophytinization of bacteriochlorophyll (BChl) in the membranes of chromatophores isolated from normal and carotenoidless cells of the purple bacterium Allochromatium minutissimum as well as in the core complexes and peripheral light harvesting complexes in the media with different detergents at low pH values. The well-marked staging of damage of native BChl forms with the absorption band of 885 nm has been revealed: (1) the formation and increase of the absorption band of monomeric BChl (785 nm); (2) pheophytinization of resultant monomeric BChl, and (3) aggregation of bacteriopheophytin (BPheo). Compared to the initial carotenoid complexes, carotenoidless pigment protein complexes were less resistant to the effect of low pH values, especially at the stages of BChl monomerization and pheophytinization. However, BPheo aggregation in them was slower. The electrophoresis in PAAG has shown that BChl pheophytinization in peripheral light harvesting complexes is accompanied by disruption of the ring-shaped structures of the complexes, with appearance of typical fragments consisting of α- and β- peptides and carrying monomeric BPheo, and by formation of α-peptide aggregates carrying BPheo aggregates.