CHANGES IN BACTERIOCHLOROPHYLL-C ORGANIZATION DURING ACID TREATMENT OF CHLOROSOMES FROM CHLOROBIUM-TEPIDUM

We have investigated changes in the organization of bacteriochlorophyl l c (BChl c) in chlorosomes isolated from the green sulfur bacterium C hlorobium tepidum during the formation of bacteriopheophytin and bacte riopheophorbide in acidic media. The reaction was much slower than tha t observed with BChl dissolved in methanol, suggesting that the aggreg ation of BChl or the presence of the chlorosome envelope constitutes a barrier to the reaction with protons in the aqueous phase. In most ca ses the first two-thirds of the reaction showed time courses that were close to linear. Simultaneously with the pheophytinization process we observed a red-shift of the Q(y) band of the remaining aggregated BCh l c reaching a maximum extent of 9 mn. Analysis of the spectral change s provided evidence at least for two spectrally distinct pools of aggr egated BChl c with different rates of reaction with acid. An HPLC anal ysis showed that there were no changes in the distribution of the four major homologs of BChl c remaining in chlorosomes during the course o f acid treatment, at least up to the time when two-thirds had been con verted to pheophytin, This suggests that the homologs of BChl c are un iformly distributed within the chlorosome.