THE HOMOLOGATION PROCESS OF BACTERIOCHLOROPHYLLS CF AND DF

Abstract

Chlorosomes are light-harvesting systems of green photosynthetic bacteria which contain bacteriochlorophyll (BChl) c, d and/or e molecules in a rod-like self-aggregate without any significant interaction between protein. It is not clear that many homologs exist in the chlorosomes possessing different alkyl groups at the positions 8, 12 and 20. We found that growth under limited potassium concentration enriched the BChl d homologs coexisting with BChl c homologs in chlorosomes of Cb. limicola. A similar effect was observed in the bacterium by addition of tetraethylammoniumchloride is an inhibitor for passing through the potassium channel. In vitro FT-IR study was carried out with bacteriochlorophyllide (BChld) to exclude the effect of farnesyl group. It showed a clear difference between each homologs of BChld c and BChld d were observed at 131 C=O group coordinated to the central Mg atom. The signal of R-BChld c shifted their coordinated 131 C=O bands to lower wavenumber region concomitant with the alkylation at position 8 and 12, but those of BChld d showed only a little changes. These results suggest that Cb. limicola requires R-BChl c to form rod-like self-aggregates and individual homologs form their own structures to create heterogeneity in the rod structures.