Studies on autotrophic CO fixation by the filamentous anoxygenic photosynthetic bacterium strain DG-6 demonstrated that, unlike other green bacteria, this organism metabolized CO via the reductive pentose phosphate cycle. Both key enzymes of this cycle — ribulose-1,5-bisphosphate carboxylase/oxygenase and phosphoribulokinase — were detected in cell extracts. The main product of ribulose 1,5-bisphosphate-dependent CO fixation was 3-phosphoglyceric acid. KCN, which is known to be a competitive inhibitor of ribulose-1,5-bisphosphate carboxylase/oxygenase, completely in hibited the CO assimilation by whole cells as well as by cell extracts of The C/C carbon isotope fractionation during photoautotrophic growth of was -19·7°/∞, which is close to that obtained for autotrophic organisms that use ribulose-1,5-bisphosphate carboxylase as the primary carboxylation enzyme. Cell extracts of contained all the enzymes of the tricarboxylic acid cycle except 2-oxoglutarate dehydrogenase. No activity of isocitrate lyase, a key enzyme of the glyoxylate shunt, was found in cell extracts of DG-6.


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