A 6.3 kDa polypeptide has been isolated from chlorosomes of the green photosynthetic bacterium Pelodictyon luteolum, and its complete amino acid sequence has been determined. It exhibits an overall homology of 30% to the Bchlc‐binding protein of Chloroflexus aurantiacus. Preliminary results from the N‐terminal sequence analyses of the analogous polypeptides isolated from Chlorobium limicola, Prosthecochloris aestuarii and chlorobium phaeovibrioides revealed a highly conserved sequence. This protein is suggested to be the Bchlc/e‐binding polypeptide in the family of the Chlorobiaceae.

Antenna polypeptides from two species of the family Ectothiorhodospiraceae have been investigated. By means of gel filtration and subsequent high‐performance liquid chromatography, at least five polypeptides were isolated from each of Ectothiorhodospira halochloris and Ectothiorhodospira halophila. The majority of their primary structures was identified by Edman degradation. Comparison of these polypeptide sequences with the known primary structures of antenna polypeptides from various purple non‐sulfur bacteria revealed interesting new aspects with regard to the structure of the core‐peripheral antenna system. E. halochloris and E. halophila contain two pairs of α‐ and β‐polypeptides each with typical primary structure elements of core complexes, indicating a modified antenna complex organization.

Whole cells from Ectothiorhodospira halochloris were extracted with an organic solvent mixture. At least five small hydrophobic polypeptides representing most probably the light harvesting polypeptides were purified by gel filtration and consecutive FPLC-RP chromatography. The complete amino acid sequence of a 7.4 kDa polypeptide was determined. The polypeptide shows a three domain structure, indicative of an integral membrane protein, similar to the structure of the light-harvesting polypeptides from purple non-sulfur bacteria. Sequence homologies to the fl-LHPs of purple bacteria range from 23. !% to 36.4~;. The conserved intramembrane located histidine residue of the antenna polypeptides of purple non-sulfur bacteria, assigned as the possible binding site for bacteriochlorophyll, was found to be replaced by asparagine.Purple bacteria; Bacteriochlorophyll b; Light-harvesting polypeptide; Amino acid sequence; (Ectothiorhodospira halochloris)

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In addition to the previous isolated and sequenced polypeptides from green photosynthetic sulfur bacteria, which are presumably involved in binding BChl c and e, an analogous poly- peptide has been purified from the BChl d-containing bacterium Chlorobium vibrioforme f. thiosulfatophilum. The primary structure of this 6.15 kDa polypeptide was determined. It shows an extremely high homology (98.3%) to the corresponding polypeptide from Pelodictyon luteolum, indicative of an important functional role.