A pathway of the autotrophic CO2 fixation in Chloroflexus aurantiacus

Ivanovsky, R. N.; Krasil’nikova, E. N.; Fal, Yuri I.

doi:10.1007/bf00248481

Cited by 42 publications

(24 citation statements)

References 27 publications

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“…Preparation of [1,2,[3][4][5][6][7][8][9][10][11][12][13] C 3 ]Propionyl-CoA-A reaction mixture (20 ml) containing 100 mM Tris/HCl buffer, pH 8.4, 2 mM MgCl 2 , 3 mM CoA, 3 mM [1,2,[3][4][5][6][7][8][9][10][11][12][13] C 3 ]sodium propionate, 7.5 mM ATP, 4 mM NADH, 10 units of acetyl-CoA synthetase, 10 units of myokinase, 5 mM PEP, 30 units of pyruvate kinase, and 28 units of L-lactate dehydrogenase was adjusted to pH 8.4 by addition of KOH. The mixture was incubated at 30°C.…”

Section: Preparation Of [2-14 C]propionyl-coa-[2-mentioning

confidence: 99%

“…An acetyl-CoA-dependent conversion of glyoxylate to malyl-CoA and malate was ascribed to the reverse reaction of malyl-CoA lyase forming malyl-CoA, combined with a side reaction of citrate synthase or acyl-CoA thioesterase, which hydrolyzes malyl-CoA to malate and CoA (7,(13)(14)(15). Previous studies have shown that C. aurantiacus can use pyruvate for anaplerotic reactions (3,7,11,16). Pyruvate is converted to phosphoenolpyruvate (PEP) 1 by pyruvate phosphate dikinase, followed by PEP carboxylation to oxaloacetate by PEP carboxylase.…”

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confidence: 99%

“…The pathway of glyoxylate assimilation into cell material is incompletely understood (5)(6)(7)(8)(9)(10)(11)(12). Glycine has been ruled out as an intermediate (7).…”

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A Bicyclic Autotrophic CO2 Fixation Pathway in Chloroflexus aurantiacus

Herter¹,

Fuchs²,

Bacher³

et al. 2002

Journal of Biological Chemistry

131

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Phototrophic CO 2 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 malylCoA affording glyoxylate (the primary CO 2 fixation product) with regeneration of acetyl-CoA serving as the starter unit of the cycle. Cell extracts of C. aurantiacus were also shown to catalyze the conversion of citramalate into pyruvate and acetyl-CoA in a succinyl-CoAdependent reaction. The data suggest that glyoxylate obtained by the cleavage of malyl-CoA can be utilized by condensation with propionyl-CoA affording erythro-␤-methylmalyl-CoA, which is converted to acetyl-CoA and pyruvate. This reaction sequence regenerates acetylCoA, which serves as the precursor of propionyl-CoA in the 3-hydroxypropionate cycle. Autotrophic CO 2 fixation proceeds by combination of the 3-hydroxypropionate cycle with the methylmalyl-CoA cycle. The net product of that bicyclic autotrophic CO 2 fixation pathway is pyruvate serving as an universal building block for anabolic reactions.Autotrophic CO 2 fixation in the phototrophic bacterium Chloroflexus aurantiacus has been proposed to proceed via a novel pathway, the 3-hydroxypropionate cycle ( Fig. 1) (1-7). Briefly, acetyl-CoA (1) serves as starting unit, and biotin-dependent carboxylation of acetyl-CoA and propionyl-CoA (4) are the main CO 2 fixation reactions. One turn of the proposed cycle results in conversion of acetyl-CoA into malyl-CoA (8) with consumption of 2 HCO 3 Ϫ and 3 NADPH. Malyl-CoA is cleaved by malyl-CoA lyase with regeneration of the starting molecule acetyl-CoA. Glyoxylate (9) is believed to be the initial CO 2 fixation product (7).The pathway of glyoxylate assimilation into cell material is incompletely understood (5-12). Glycine has been ruled out as an intermediate (7). So far, in vitro transformation of glyoxylate has not been observed, except for pyridine nucleotide-dependent reduction to glycolate (7). An acetyl-CoA-dependent conversion of glyoxylate to malyl-CoA and malate was ascribed to the reverse reaction of malyl-CoA lyase forming malyl-CoA, combined with a side reaction of citrate synthase or acyl-CoA thioesterase, which hydrolyzes malyl-CoA to malate and CoA (7,(13)(14)(15). Previous studies have shown that C. aurantiacus can use pyruvate for anaplerotic reactions (3,7,11,16). Pyruvate is converted to phosphoenolpyruvate (PEP) 1 by pyruvate phosphate dikinase, followed by PEP carboxylation to oxaloacetate by PEP carboxylase. However, pyruvate synthase activity was hardly detectable (12), and the origin of pyruvate in C. aurantiacus is still unknown. To serve as a central intermediate for anaplerotic reactions, it should be formed ultimately from one of the intermediates of the 3-hydroxypropionate cycle and/or from glyoxylate.The aim of this work was to elucidate reactions for glyoxylate assimilation. We show that a reaction sequence starting with glyoxylate and propionyl-CoA afford...

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Section: Preparation Of [2-14 C]propionyl-coa-[2-mentioning

confidence: 99%

mentioning

confidence: 99%

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A Bicyclic Autotrophic CO2 Fixation Pathway in Chloroflexus aurantiacus

Herter¹,

Fuchs²,

Bacher³

et al. 2002

Journal of Biological Chemistry

131

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“…A different pathway has been proposed in which acetyl-CoA is reductively carboxylated to pyruvate by ferredoxin-dependent pyruvate synthase (19,21). Pyruvate then can be converted to phosphoenolpyruvate (PEP) and oxaloacetate via pyruvate phosphate dikinase and PEP carboxylase.…”

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confidence: 99%

“…by which glyoxylate is converted into a central biosynthetic intermediate, such as acetyl-CoA, pyruvate, or oxaloacetate. Some proposals were made, but experimental evidence was scarce (12,19,20,21,39,40). These proposals included the following: (i) condensation of two molecules of glyoxylate to form tartronate semialdehyde and subsequent reduction to glyceratethis proposal suffers from the fact that CO 2 is released, not a useful trait of a CO 2 fixation mechanism; (ii) conversion of glycine to a one-carbon unit, again with the release of CO 2 , and reassimilation of the one-carbon unit by condensation with glycine, forming serine-the same objection applies to this proposal; (iii) conversion of one molecule of glyoxylate to glycine and condensation of another molecule of glyoxylate with glycine, forming hydroxyaspartate, or any other condensation reaction of glycine; and (iv) glycine reduction to acetylphosphate.…”

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Autotrophic CO ₂ Fixation by Chloroflexus aurantiacus : Study of Glyoxylate Formation and Assimilation via the 3-Hydroxypropionate Cycle

et al. 2001

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In the facultative autotrophic organism Chloroflexus aurantiacus, a phototrophic green nonsulfur bacterium, the Calvin cycle does not appear to be operative in autotrophic carbon assimilation. An alternative cyclic pathway, the 3-hydroxypropionate cycle, has been proposed. In this pathway, acetyl coenzyme A (acetyl-CoA) is assumed to be converted to malate, and two CO 2 molecules are thereby fixed. Malyl-CoA is supposed to be cleaved to acetyl-CoA, the starting molecule, and glyoxylate, the carbon fixation product. Malyl-CoA cleavage is shown here to be catalyzed by malyl-CoA lyase; this enzyme activity is induced severalfold in autotrophically grown cells. Malate is converted to malyl-CoA via an inducible CoA transferase with succinyl-CoA as a CoA donor. Some enzyme activities involved in the conversion of malonyl-CoA via 3-hydroxypropionate to propionyl-CoA are also induced under autotrophic growth conditions. So far, no clue as to the first step in glyoxylate assimilation has been obtained. One possibility for the assimilation of glyoxylate involves the conversion of glyoxylate to glycine and the subsequent assimilation of glycine. However, such a pathway does not occur, as shown by labeling of whole cells with [1,2-13 C 2 ]glycine. Glycine carbon was incorporated only into glycine, serine, and compounds that contained C 1 units derived therefrom and not into other cell compounds.

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