Pathway of anaerobic poly-?-hydroxybutyrate degradation byIlyobacter delafieldii

Janssen, Peter H.; Schink, Bernhard

doi:10.1007/bf00695120

Cited by 42 publications

(23 citation statements)

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“…Cells were harvested in the late logarithmic phase (25 days for acetone-grown cultures and 15 to 18 days for 3-hydroxybutyrate-grown cultures) by centrifugation under strictly anoxic conditions as previously described (20), and then they were washed and resuspended in anoxic 125 mM triethanolamine ⅐ HCl (pH 7.4) containing 2.5 mM dithioerythritol. Cell extracts were prepared by French press treatment as described elsewhere (20).…”

Section: Methodsmentioning

confidence: 99%

Catabolic and anabolic enzyme activities and energetics of acetone metabolism of the sulfate-reducing bacterium Desulfococcus biacutus

Janssen

Schnik

1995

J Bacteriol

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Acetone degradation by cell suspensions of Desulfococcus biacutus was CO 2 dependent, indicating initiation by a carboxylation reaction, while degradation of 3-hydroxybutyrate was not CO 2 dependent. Growth on 3-hydroxybutyrate resulted in acetate accumulation in the medium at a ratio of 1 mol of acetate per mol of substrate degraded. In acetone-grown cultures no coenzyme A (CoA) transferase or CoA ligase appeared to be involved in acetone metabolism, and no acetate accumulated in the medium, suggesting that the carboxylation of acetone and activation to acetoacetyl-CoA may occur without the formation of a free intermediate. Catabolism of 3-hydroxybutyrate occurred after activation by CoA transfer from acetyl-CoA, followed by oxidation to acetoacetyl-CoA. In both acetone-grown cells and 3-hydroxybutyrate-grown cells, acetoacetyl-CoA was thiolytically cleaved to two acetyl-CoA residues and further metabolized through the carbon monoxide dehydrogenase pathway. Comparison of the growth yields on acetone and 3-hydroxybutyrate suggested an additional energy requirement in the catabolism of acetone. This is postulated to be the carboxylation reaction (⌬G؇ for the carboxylation of acetone to acetoacetate, ؉17.1 kJ ⅐ mol ؊1). At the intracellular acyl-CoA concentrations measured, the net free energy change of acetone carboxylation and catabolism to two acetyl-CoA residues would be close to 0 kJ ⅐ mol of acetone ؊1, if one mol of ATP was invested. In the absence of an energy-utilizing step in this catabolic pathway, the predicted intracellular acetoacetyl-CoA concentration would be 10 13 times lower than that measured. Thus, acetone catabolism to two acetyl-CoA residues must be accompanied by the utilization of the energetic equivalent of (at least) one ATP molecule. Measurement of enzyme activities suggested that assimilation of acetyl-CoA occurred through a modified citric acid cycle in which isocitrate was cleaved to succinate and glyoxylate. Malate synthase, condensing glyoxylate and acetyl-CoA, acted as an anaplerotic enzyme. Carboxylation of pyruvate or phosphoenolpyruvate could not be detected.The anaerobic metabolism of acetone appears to involve an initial carboxylation of acetone to acetoacetate (or acetoacetyl coenzyme A [acetoacetyl-CoA]), followed by thiolytic cleavage to two acetyl-CoA residues (3, 32-35). The carboxylation reaction has not been measured in vitro, and evidence has come from 14 C labelling studies (32,33,35). Carboxylation reactions appear to play a role in a number of anaerobic transformations (16, 44), but these reactions have not been well studied. The carboxylation of acetone to acetoacetate, CH 3 COCH 3 ϩ HCO 3), is an endergonic reaction (42). Thus, the energetic equivalent of about 1/3 mol of ATP (⌬GЊЈ of ATP hydrolysis, Ϫ50 kJ ⅐ mol Ϫ1 [42]) is required, but the mechanism of coupling is not known. In addition, attempts to measure the carboxylase in sulfate-reducing bacteria have remained unsuccessful (21).Many genera of sulfate-reducing bacteria are able to oxidize completely (to CO ...

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Section: Methodsmentioning

confidence: 99%

Catabolic and anabolic enzyme activities and energetics of acetone metabolism of the sulfate-reducing bacterium Desulfococcus biacutus

Janssen

Schnik

1995

J Bacteriol

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“…Catalase (29) and superoxide dismutase (33) activities were assayed by using cell extracts that were prepared by French press treatment under anoxic conditions (18).…”

Section: Methodsmentioning

confidence: 99%

Lactosphaera gen. nov., a New Genus of Lactic Acid Bacteria, and Transfer of Ruminococcus pasteurii Schink 1984 to Lactosphaera pasteurii comb. nov.

Janssen

Evers

Rainey

et al. 1995

International Journal of Systematic Bacteriology

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“…Larger culture volumes were grown in 250-ml glass bottles sealed with black rubber stoppers and containing 200ml of the same medium under a headspace of N2/CO2 (80:20;v/v). All cultures were incubated in the dark at 30~ Preparation of cell suspensions and extracts Cells were harvested by centrifugation under strictly anoxic conditions as described previously (Janssen and Schink 1993) and washed and resuspended in anoxic 125mM triethanolamine (pH adjusted to 7.4 with HC1) containing 2.5 mM dithioerythritol. Cell extracts were prepared by French press treatment as described elsewhere (Janssen and Schink 1993).…”

Section: Organism and Culture Conditionsmentioning

confidence: 99%

Metabolic pathways and energetics of the acetone-oxidizing, sulfate-reducing bacterium, Desulfobacterium cetonicum

Janssen

Schink

1995

Archives of Microbiology

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Acetone degradation by cell suspensions of Desulfobacterium cetonicum was CO2-dependent, indicating initiation by a carboxylation reaction. Degradation of butyrate was not CO2-dependent, and acetate accumulated at a ratio of 1 mol acetate per mol butyrate degraded. In cultures grown on acetone, no CoA transfer apparently occurred, and no acetate accumulated in the medium. No CoA-ligase activities were detected in cell-free crude extracts. This suggested that the carboxylation of acetone to acetoacetate; and its activation to acetoacetyl-CoA may occur without the formation of free acetoacetate. Acetoacetyl-CoA was thiolytically cleaved to two acetyl-CoA, which were oxidized to CO2 via the acetyl-CoA/carbon monoxide dehydrogenase pathway. The measured intracellular acyl-CoA ester concentrations allowed the calculation of the free energy changes involved in the conversion of acetone to acetyl-CoA. At in vivo concentrations of reactants and products, the initial steps (carboxylation and activation) must be energy-driven, either by direct coupling to ATE or coupling to transmembrane gradients. The AG' of acetone conversion to two acetyl-CoA at the expense of the energetic equivalent of one ATP was calculated to lie very close to 0kJ (mol acetone) ~. Assimilatory metabolism was by an incomplete citric acid cycle, lacking an activity oxidatively decarboxylating 2-oxoglutarate. The low specific activities of this cycle suggested its probable function in anabolic metabolism. Succinate and glyoxylate were formed from isocitrate by isocitrate lyase. Glyoxylate thus formed was condensed with acetylCoA to form malate, functioning as an anaplerotic sequence. A glyoxylate cycle thus operates in this strictly anaerobic

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Pathway of anaerobic poly-?-hydroxybutyrate degradation byIlyobacter delafieldii

Cited by 42 publications

References 23 publications

Catabolic and anabolic enzyme activities and energetics of acetone metabolism of the sulfate-reducing bacterium Desulfococcus biacutus

Catabolic and anabolic enzyme activities and energetics of acetone metabolism of the sulfate-reducing bacterium Desulfococcus biacutus

Lactosphaera gen. nov., a New Genus of Lactic Acid Bacteria, and Transfer of Ruminococcus pasteurii Schink 1984 to Lactosphaera pasteurii comb. nov.

Metabolic pathways and energetics of the acetone-oxidizing, sulfate-reducing bacterium, Desulfobacterium cetonicum

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