Enzymes of a novel autotrophic CO2 fixation pathway in the phototrophic bacterium Chloroflexus aurantiacus, the 3-hydroxypropionate cycle.
The phototrophic bacterium Chloroflexus aurantiacus can grow autotrophically but seems not to assimilate CO2 via any of the known autotrophic pathways. Holo [Holo, H. (1989) Arch. Microbiol. 151, 252-256] proposed a new pathway in which 3-hydroxypropionate is formed from acetyl-CoA. Previous studies excluded the operation of known CO2 fixation pathways and provided indirect evidence for the suggested pathway based on 13C-labelling experiments. Here all enzyme activities of the postulated cyclic CO2 fixation mechanism are demonstrated in vitro. In essence, acetyl-CoA is carboxylated and reductively converted via 3-hydroxypropionate to propionyl-CoA. Propionyl-CoA is carboxylated and converted via succinyl-CoA and CoA transfer to malyl-CoA. Malyl-CoA is cleaved to acetyl-CoA and glyoxylate. Thereby, the first CO2 acceptor molecule acetyl-CoA is regenerated, completing the cycle and the net CO2 fixation product glyoxylate is released. This cycle represents the fourth autotrophic pathway in nature and is designated the 3-hydroxypropionate cycle.
Strauss
G
G
Angewandte Mikrobiologie, Universität Ulm, Germany.
Fuchs
G
G
D000105:Acetyl Coenzyme A / Q000096:biosynthesis / Q000378:metabolism; D000214:Acyl Coenzyme A / Q000096:biosynthesis / Q000378:metabolism; D001419:Bacteria / Q000201:enzymology / Q000378:metabolism*; D002245:Carbon Dioxide / Q000378:metabolism*; D004798:Enzymes / Q000378:metabolism; D006038:Glyoxylates / Q000378:metabolism; D007773:Lactates / Q000378:metabolism*; D019344:Lactic Acid / Q000031:analogs & derivatives*
D000214:Acyl Coenzyme A; D004798:Enzymes; D006038:Glyoxylates; D007773:Lactates; D002245:Carbon Dioxide; C042519:malyl-coenzyme A; C009061:propionyl-coenzyme A; D019344:Lactic Acid; D000105:Acetyl Coenzyme A; C012046:succinyl-coenzyme A; C031601:hydracrylic acid; C031150:glyoxylic acid