Assaying for the 3-hydroxypropionate cycle of carbon fixation.
The 3-hydroxypropionate cycle is a novel pathway for autotrophic CO2 fixation, which has been demonstrated in the thermophilic phototrophic bacterium Chloroflexus aurantiacus; a yet to be defined variant of this pathway occurs in autotrophic members of the Sulfolobales (Crenarchaeota). The 3-hydroxypropionate cycle consists of the conversion of acetyl-CoA to succinyl-CoA, via malonyl-CoA, 3-hydroxypropionate, propionyl-CoA, and methylmalonyl-CoA. Carboxylation of acetyl-CoA and propionyl-CoA by acetyl-CoA/propionyl-CoA carboxylase are the CO2 fixation reactions. Succinyl-CoA serves as a precursor of cell carbon and also as a precursor of the starting compound acetyl-CoA. In C. aurantiacus, the cycle is completed by converting succinyl-CoA to malyl-CoA and cleaving malyl-CoA to acetyl-CoA and glyoxylate. Glyoxylate is then converted in a second cyclic pathway to pyruvate, which serves as a universal cell carbon precursor. The fate of succinyl-CoA in Sulfolobales is at issue. Assays used to study the characteristic enzymes of this novel pathway in C. aurantiacus are reported.
Hügler
Michael
M
Faculty of Biology, University of Freiburg, Germany.
Fuchs
Georg
G
D000103:Acetyl-CoA Carboxylase / Q000032:analysis; D002245:Carbon Dioxide / Q000378:metabolism*; D041861:Chloroflexus / Q000378:metabolism*; D003066:Coenzyme A Ligases / Q000032:analysis; D015256:Coenzyme A-Transferases / Q000032:analysis; D019344:Lactic Acid / Q000031:analogs & derivatives* / Q000378:metabolism; D043586:Methylmalonyl-CoA Decarboxylase / Q000032:analysis; D010088:Oxidoreductases / Q000032:analysis; D007652:Oxo-Acid-Lyases / Q000032:analysis; D016943:Sulfolobaceae / Q000378:metabolism
D002245:Carbon Dioxide; D019344:Lactic Acid; C031601:hydracrylic acid; D010088:Oxidoreductases; C454539:malonyl-Coa reductase; D015256:Coenzyme A-Transferases; D007652:Oxo-Acid-Lyases; C021536:malyl-CoA lyase; D003066:Coenzyme A Ligases; C068072:propionate - CoA ligase; D000103:Acetyl-CoA Carboxylase; D043586:Methylmalonyl-CoA Decarboxylase