[Bacteriochlorophyll a synthesis in Rhodopseudomonas palustris]

By means of electron microscope it was demonstrated that photosynthetically-grown Rhodopseudomonas palustris exhibits an intracytoplasmic membrane system (Figure 1a), which is not observed in aerobically-dark grown bacteria (Figure 1b). The content of bacteriochlorophyll alpha and the enzyme activity of succinil-CoA-synthetase, ALA-sinthetase and ALA-dehydratase in several media grown Rhodopseudomonas palustris could be measured. Aerobically-dark grown cells do not synthetize bacteriochlorophyll alpha and the activity of ALA-synthetase is lower than in photosynthetically-grown cells (Table 1), suggesting a possible regulatory role for this enzyme in the pigment biosynthesis. Some inhibitors of electron transport and uncouplers of photophosphorylation inhibit both the bacterial growth and bacteriochlorophyll alpha biosynthesis (Table 2), while the levels of ALA-synthetase are not affected. If the incubation in the presence of these kinds of compounds is prolongated, the effects disappear. Although the regulatory role of ALA-synthetase should be very important, apparently it would not be the unique regulatory factor for bacteriochlorophyll alpha biosynthesis in Rhodopseudomonas palustris.