EFFECTS OF 31R- AND 31S-EPIMERS OF BACTERIOCHLOROPHYLL E ON THEIR SELF-AGGREGATES IN CHLOROSOMES OF BROWN-COLORED GREEN SULFUR BACTERIA: AN ADVANTAGE AROUND 520 NM ABSORPTION IN Cb. phaeobacteroides.

Abstract

Brown-colored green sulfur bacteria such as Chlorobium (Cb.) phaeobacteroides contain a large amount of bacteriochlorophyll (BChl) e. BChl e has a formyl group at position 7 such as chlorophyll b. We found that Cb. phaeobacteroides grows under quite low light strength compared to Cb. tepidum and Cb. limicola containing BChl c. The major homologs of BChl eF (R-[E,E], R-[P,E], S-[P,E] and S-[I,E] BChl eF) were isolated from Cb. phaeobacteroides. In vitro self-aggregates of 31R-BChl eF formed in aqueous dimethyl sulfoxides solution showed the Qx-like absorption band at 520 nm corresponding to same absorption band of Cb. phaeobacteroides. 31 R- and 31 S-epimers of BChl eF isolated from Cb. phaeobacteroides showed different aggregation behavior in dicholoromethane. Self-aggregates of 31 R-epimer of BChl eF showed the Qx-like absorption band, whereas 31 S-epimer of BChl eF did not. FT-IR study of 31R-BChl eF self-aggregates showed free 7-CHO group and different coordination from 31 R-BChl cF self-aggregates. These results suggest that 7-CHO group of BChl eF in self-aggregates does not affect on vibrational band but does on Qx region electronic band. We propose that Cb. phaeobacteroides can use the Qx-like absorption band for antenna using aggregates of 31 R-epimer of BChl eF rather than 31 S-epimer.