Search PubMed⌕ Search

Biomedical subjects

R K Thauer

Publications and source records attributed to R K Thauer.

At least 163 records · Page 9Linked to original sources
PubMed1984

Evidence for a nickel-containing carbon monoxide dehydrogenase in Methanobrevibacter arboriphilicus.

In growing cultures of Methanobrevibacter arboriphilicus (Methanobrevibacter arboriphilus), the synthesis of active carbon monoxide dehydrogenase required nickel. The 21-fold-purified enzyme from 63Ni-labeled cells of M. arboriphilicus comigrated with 63Ni during gel filtration. These results provide evidence that the carbon monoxide dehydrogenase of methanogens is a nickel protein.

Aldehyde Oxidoreductases↗
PubMed1983

Uroporphyrinogen III, an intermediate in the biosynthesis of the nickel-containing factor F430 in Methanobacterium thermoautotrophicum.

Factor F430 is a nickel-containing porphinoid present in methanogenic bacteria. The synthesis of this nickel tetrapyrrole from 5-aminolevulinic acid was studied in Methanobacterium thermoautotrophicum. This anaerobic archaebacterium was found to accumulate [14C]uroporphyrinogen III (1.8 mumol/g) when growing on nickel-free medium (less than 50 nmol/l) supplemented with 2 mM 5-amino-[14C]levulinic acid. The accumulated urophorphyrinogen III was quantitatively converted to factor F430 when the cells were incubated in aminolevulinate-free medium with 5 microM NiCl2. The newly synthesized factor had the same specific radioactivity as the precursor uroporphyrinogen III. These findings indicate that the nickelporphinoid is biosynthetically derived from uroporphyrinogen III. The presence and some properties of the enzymes catalyzing the synthesis of uroporphyrinogen III from 5-aminolevulinic acid in M. thermoautotrophicum are also described.

Aminolevulinic Acid↗
PubMed1982

Dissimilatory sulphate reduction with acetate as electron donor.

Acetate oxidation by sulphate was studied with desulfobacter postgatei. Cell extracts of the organism were found to contain high activities of the following enzymes: citrate synthase, aconitase, isocitrate dehydrogenase, alpha-ketoglutarate dehydrogenase, succinate dehydrogenase, fumarase, malate dehydrogenase and pyruvate synthase. It is concluded that acetate oxidation with sulphate in D. postgatei proceeds via the citric acid cycle with the synthesis of pyruvate from acetyl CoA and CO2 as an anaplerotic reaction. The apparent Ks for acetate oxidation by D. postgatei as determined in vivo was near 0.2 mM. The apparent Ks for acetate fermentation to methane and CO2 by methanosarcina barkeri was 3 mM. The significantly lower ks for acetate of the sulphate reducer explains why methane formation from acetate in natural habitats is apparently inhibited by sulphate.

Acetates↗
PubMed1981

Nickel requirement and factor F430 content of methanogenic bacteria.

Methanobacterium thermoautotrophicum has been reported to require nickel for growth and to contain high concentrations of a nickel tetrapyrrole designated factor F430. In this communication it is shown that all methanogenic bacteria investigated incorporated nickel during growth and also synthesized factor F430. This was also true for Methanobrevibacter smithii, which is dependent on acetate as a carbon source, and for Methanosarcina barkeri growing on acetate or methanol as energy sources. Other bacteria, including Acetobacterium woodii and Clostridium thermoaceticum, contained no factor F430. It is further shown that two yellow nickel-containing degradation products were formed from factor F430 when heated at pH 7. This finding explains why several forms of factor F430 were found in methanogenic bacteria when a heat step was employed in the purification procedure.

Euryarchaeota↗
PubMed1980

Acetate thiokinase and the assimilation of acetate in methanobacterium thermoautotrophicum.

Methanobacterium thermoautotrophicum growing on H2 plus CO2 as sole carbon and energy source was found to contain acetate thiokinase (Acetyl CoA synthetase; EC 6.2.1.1); Acetate + ATP + CoA leads to Acetyl CoA + AMP + PPi. The apparent Km value for acetate was 40 microM. Acetate kinase (EC 2.7.2.1) and phosphotransacetylase (EC 2.3.1.8) could not be detected. The specific activity of acetate thiokinase was high in cells grown with limited H2 and CO2 supply (approximately 100 nmol/min . mg protein), it was low in exponentially grown cells (2 nmol/min . mg protein). This corresponded with the finding that cells growing linearly in the presence of acetate assimilated the monocarboxylic acid in high amounts (greater than 10% of the cell carbon was derived from acetate), whereas exponentially growing cells did not (less than 1% of cell carbon was derived from acetate). These latter observations indicated that acetate thiokinase and free acetate are not involved in autotrophic CO2 fixation in M. thermoautotrophicum. The presence and some kinetic properties of succinate thiokinase (EC 6.2.1.5), adenylate kinase (EC 2.7.4.3), and inorganic pyrophosphatase (EC 3.6.1.1) are also described.

Acetate-CoA Ligase↗
PubMed1980

Incorporation of 8 succinate per mol nickel into factors F430 by Methanobacterium thermoautotrophicum.

Factors F430 from methanogenic bacteria have recently been shown to contain nickel and it has been speculated that they may have a nickel tetrapyrrole structure. This assumption was tested by determining whether succinate is incorporated by growing Methanobacterium thermoautotrophicum into three factors F430. Succinate is assimilated by Methanobacterium thermoautotrophicum into the amino acids glutamate, arginine and proline and into tetrapyrroles rather than other cell components. It was found that per mol nickel 8--9 mol of succinate were incorporated into the three factors F430 which is the amount predicted for a tetrapyrrole structure. Since the three factors F430 only contained significant amounts of glutamate rather than arginine or proline, the incorporation data suggest that factors F430 are nickel tetrapyrrole compounds. Spectral properties of the three factors F430, apparent molecular weights, and the absence of phosphor in these compounds are also described.

Amino Acids↗
PubMed1980

Nickel, a component of factor F430 from Methanobacterium thermoautotrophicum.

Methanobacterium thermoautotrophicum, growing on medium supplemented with 2 mumol 63NiCl2/l, was found to take up 1.2 mumol 63Ni per g cells (dry weight). More than 70% of the radioisotope was incorporated into a compound, which dissociated from the protein fraction after heat treatment, was soluble in 70% acetone, and could be purified by chromatography on QAE-Sephadex A-25, Sephadex G-25, and DEAE cellulose. The purified 63Ni labelled compound had an absorption spectrum and properties identical to those of factor F430 and is therefore considered to be identical with factor F430.

Cell Fractionation↗
PubMed1979

Ferredoxin degradation in growing Clostridium pasteurianum during periods of iron deprivation.

Clostridium pasteurianum was grown in batch cultures on media with an initial iron concentration of 10 micron. The uptake of iron and the synthesis of ferredoxin was followed. All the iron present in the medium was taken up by the cells before 50% of the final cell density was attained. The bacteria then continued to grow in the complete absence of exogenous iron. Ferrodoxin was synthesized during growth until the exogenous iron concentration dropped below 1 micron. During growth in the absence of iron ferredoxin was degraded with the result that at the end of growth the cells did not contain ferredoxin. The specific activity of the iron sulfur protein, pyruvate synthase (E.C. 1.2.7.1), remained constant during growth of C. pasteurianum in the absence of exogenous iron. This finding suggest that ferredoxin was used as an endogenous source of iron for the synthesis of essential iron proteins during periods of iron deprivation.

Biodegradation, Environmental↗
PubMed1979

Nickel, cobalt, and molybdenum requirement for growth of Methanobacterium thermoautotrophicum.

Growth of Methanobacterium thermoautotrophicum on H2 and CO2 as sole energy and carbon sources was found to be dependent on Ni, Co, and Mo. At low concentrations of Ni (less than 100 nM), Co (less than 10 nM) and Mo (less than 10 nM) the amount of cells formed was roughly proportional to the amount of transition metal added to the medium; for the formation of 1 g cells (dry weight) approximately 150 nmol NiCl2, 20 nmol CoCl2 and 20 nmol Na2MoO4 were required. A dependence of growth on Cu, Mn, Zn, Ca, Al, and B could not be demonstrated. Conditions are described under which the bacterium grew exponentially with a doubling time of 1.8 h up to a cell density of 2 g cells (dry weight)/l.

Carbon Dioxide↗
PubMed1978

Acetate assimilation and the synthesis of alanine, aspartate and glutamate in Methanobacterium thermoautotrophicum.

Cultures of the autotrophic bacterium Methanobacterium thermoautotrophicum were shown to assimilate acetate when grown on CO2 and H2 in the presence of acetate. At 1 mM acetate 10% of the cell carbon came from acetate, the rest from CO2. At higher concentrations the percentage increased to reach a maximum of 65% at acetate concentrations higher than 20 mM. The data suggest that acetate may be an important carbon source under physiological conditions. The incorporation of acetate into alanine, aspartate and glutamate was studied in more detail. The cells were grown on CO2 and H2 in the presence of 1 mM U-14C-acetate. The three amino acids were isolated from the labelled cells by a simplified procedure. Alanine, aspartate and glutamate were found to have the same specific radioactivity. Degradation studies showed that C1 of alanine, C1 and C4 of aspartate, and C1 and C5 of glutamate were exclusively derived from CO2, whereas C2 and C3 of alanine and aspartate, and C3 and C4 of glutamate were partially derived from acetate. These findings and the presence of pyruvate synthase, phosphoenolpyruvate carboxylase and alpha-ketoglutarate synthase in M. thermoautotrophicum indicate that CO2 is assimilated into the three amino acids via acetyl CoA carboxylation to pyruvate, phosphoenolpyruvate carboxylation to oxaloacetate, and succinyl CoA carboxylation to alpha-ketoglutarate.

Acetates↗