Publications

• Anaerobic pyruvate metabolism of Tritrichomonas foetus and Trichomonas vaginalis hydrogenosomes.

  Steinbuchel A., Muller M.

  Hydrogenosomes isolated from Tritrichomonas foetus and Trichomonas vaginalis fermented pyruvate to acetate, malate, H2, and CO2 in an anaerobic process dependent on ADP, Pi, Mg2+, and succinate. The extent to which pyruvate was carboxylated to malate by malate dehydrogenase (decarboxylating) rathe ... >> More

  Hydrogenosomes isolated from Tritrichomonas foetus and Trichomonas vaginalis fermented pyruvate to acetate, malate, H2, and CO2 in an anaerobic process dependent on ADP, Pi, Mg2+, and succinate. The extent to which pyruvate was carboxylated to malate by malate dehydrogenase (decarboxylating) rather than decarboxylated to acetate by pyruvate/ferredoxin oxidoreductase was dependent on pCO2. The processes observed showed carbon and redox balances. The presence of an NADH/ferredoxin oxidoreductase activity was demonstrated. This enzyme is likely to be involved in the transfer of electrons from the ferredoxin reduced in pyruvate oxidation to NAD+ needed for the reductive carboxylation of pyruvate. Disruption of hydrogenosomes with Triton X-100 led to cessation of pyruvate-dependent H2 formation which could be restored by addition of coenzyme A and methyl viologen or ferredoxin. The formation of acetate and H2 by undisrupted hydrogenosomes proceeded at approximately half maximal rates in the presence of 25 microM succinate for T. foetus and 5 microM succinate for T. vaginalis. The apparent Km value of the acetate/succinate CoA transferase from T. foetus for succinate was approximately 45 microM, thus the stimulating effect of succinate might be due to the requirement of this enzyme for succinate. The exact mechanism of this effect remains to be elucidated, however. << Less

  Mol Biochem Parasitol 20:57-65(1986) [PubMed] [EuropePMC]

• A specialized citric acid cycle requiring succinyl-coenzyme A (CoA):acetate CoA-transferase (AarC) confers acetic acid resistance on the acidophile Acetobacter aceti.

  Mullins E.A., Francois J.A., Kappock T.J.

  Microbes tailor macromolecules and metabolism to overcome specific environmental challenges. Acetic acid bacteria perform the aerobic oxidation of ethanol to acetic acid and are generally resistant to high levels of these two membrane-permeable poisons. The citric acid cycle (CAC) is linked to ace ... >> More

  Microbes tailor macromolecules and metabolism to overcome specific environmental challenges. Acetic acid bacteria perform the aerobic oxidation of ethanol to acetic acid and are generally resistant to high levels of these two membrane-permeable poisons. The citric acid cycle (CAC) is linked to acetic acid resistance in Acetobacter aceti by several observations, among them the oxidation of acetate to CO2 by highly resistant acetic acid bacteria and the previously unexplained role of A. aceti citrate synthase (AarA) in acetic acid resistance at a low pH. Here we assign specific biochemical roles to the other components of the A. aceti strain 1023 aarABC region. AarC is succinyl-coenzyme A (CoA):acetate CoA-transferase, which replaces succinyl-CoA synthetase in a variant CAC. This new bypass appears to reduce metabolic demand for free CoA, reliance upon nucleotide pools, and the likely effect of variable cytoplasmic pH upon CAC flux. The putative aarB gene is reassigned to SixA, a known activator of CAC flux. Carbon overflow pathways are triggered in many bacteria during metabolic limitation, which typically leads to the production and diffusive loss of acetate. Since acetate overflow is not feasible for A. aceti, a CO(2) loss strategy that allows acetic acid removal without substrate-level (de)phosphorylation may instead be employed. All three aar genes, therefore, support flux through a complete but unorthodox CAC that is needed to lower cytoplasmic acetate levels. << Less

  J. Bacteriol. 190:4933-4940(2008) [PubMed] [EuropePMC]