Enzymes of the citramalate cycle in <Emphasis Type="Italic">Rhodospirillum rubrum</Emphasis> |
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Authors: | I A Berg R N Ivanovsky |
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Institution: | (1) Department of Microbiology, Faculty of Biology, Moscow State University, Vorobyevy Gory 1-12, Moscow, 119991, Russia |
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Abstract: | Rhodospirillum rubrum is among the bacteria that can assimilate acetate in the absence of isocitrate lyase, the key enzyme of glyoxylate shunt. Previously we have suggested the functioning of a new anaplerotic cycle of acetate assimilation in this bacterium: citramalate cycle, where acetyl-CoA is oxidized to glyoxylate. This work has demonstrated the presence of all the key enzymes of this cycle in R. rubrum extracts: citramalate synthase catalyzing condensation of acetyl-CoA and pyruvate with the formation of citramalate, mesaconase forming mesaconate from L-citramalate, and the enzymes catalyzing transformation of propionyl-CoA + glyoxylate 3-methylmalyl-CoA ? mesaconyl-CoA. At the same time, R. rubrum synthesizes crotonyl-CoA carboxylase/reductase, which is the key enzyme of ethylmalonyl-CoA pathway discovered recently in Rhodobacter sphaeroides. Physiological differences between the citramalate cycle and the ethylmalonyl-CoA pathway are discussed. |
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Keywords: | carbon metabolism glyoxylate cycle citramalate cycle acetate |
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