A bicyclic autotrophic CO2 fixation pathway in Chloroflexus aurantiacus.

被引:100
作者
Herter, S
Fuchs, G
Bacher, A
Eisenreich, W
机构
[1] Univ Freiburg, Inst Biol 2, Lehrstuhl Mikrobiol, D-79104 Freiburg, Germany
[2] Tech Univ Munich, Lehrstuhl Organ Chem & Biochem, D-85747 Garching, Germany
关键词
D O I
10.1074/jbc.M201030200
中图分类号
Q5 [生物化学]; Q7 [分子生物学];
学科分类号
071010 ; 081704 ;
摘要
Phototrophic CO2 assimilation by the primitive, green eubacterium. Chloroflexus aurantiacus has been shown earlier to proceed in a cyclic mode via 3-hydroxypropionate, propionyl-CoA, succinyl-CoA, and malyl-CoA. The metabolic cycle could be closed by cleavage of malyl-CoA affording glyoxylate (the primary CO2 fixation product) with regeneration of acetyl-CoA serving as the starter unit of the cycle. The pathway of glyoxylate assimilation to form gluconeogenic precursors has not been elucidated to date. We could now show that the incubation of cell extract with a mixture of glyoxylate and [1,2,3-C-13(3)]propionyl-CoA afforded erythro-beta-[1,2,2'-C-13(3)]methylmalate and [1,2,2'-C-13(3)]citramalate. Similar experiments using a partially purified protein fraction afforded erythro-beta-[1,2,2'-C-13(3)]methylmalyl-CoA and [1,2,2'-C-13(3)]mesaconyl-CoA. Cell extracts of C. aurantiacus were also shown to catalyze the conversion of citramalate into pyruvate and acetyl-CoA in a succinyl-CoA-dependent reaction. The data suggest that glyoxylate obtained by the cleavage of malyl-CoA can be utilized by condensation with propionyl-CoA affording erythro-beta-methylmalyl-CoA, which is converted to acetyl-CoA and pyruvate. This reaction sequence regenerates acetyl-CoA which serves as the precursor of propionyl-CoA in the 3-hydroxypropionate cycle. Autotrophic CO2 fixation proceeds by combination of the 3-hydroxypropionate cycle with the methylmalyl-CoA cycle. The net product of that bicyclic autotrophic CO2 fixation pathway is pyruvate serving as an universal building block for anabolic reactions.
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页码:20277 / 20283
页数:7
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