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  • Tetrahydromethanopterin  (9)
  • Methanogenic bacteria  (5)
  • Acetate oxidation  (2)
  • 1
    Electronic Resource
    Electronic Resource
    Different mechanisms of acetate activation in Desulfurella acetivorans and Desulfuromonas acetoxidans (1990)
    Springer
    Archives of microbiology 154 (1990), S. 274-279 
    Details
    ISSN: 1432-072X
    Keywords: Desulfurella ; Desulfuromonas ; Sulfur reduction ; Acetate oxidation ; Citric acid cycle ; Menaquinone ; Cytochromes
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Desulfurella acetivorans and Desulfuromonas acetoxidans are both acetate oxidizing sulfur reducing eubacteria. The two organisms differ in G+C content of DNA (31.4% versus 50–52%) and in growth temperature optimum (55°C versus 30°C) and in that D. acetivorans does not contain cytochromes. Both organisms are shown to be similar in that they metabolize acetate via the citric acid cycle rather than via the carbon monoxide dehydrogenase pathway. They were found to differ, however, in the mechanism of acetate activation and of succinate formation. In D. acetoxidans acetyl-CoA and succinate are formed from acetate and succinyl-CoA involving only one enzyme, succinyl-CoA: acetate CoA-transferase. In D. acetivorans acetyl-CoA is generated from acetate via acetyl phosphate involving acetate kinase and phosphate acetyltransferase; succinate is formed from succinyl-CoA via succinyl-CoA synthetase. Both sulfur reducers were found to contain menaquinone.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00248967
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  • 2
    Electronic Resource
    Electronic Resource
    Purification and properties of N 5 ,N 10 -methylenetetrahydromethanopterin reductase (coenzyme F420-dependent) from the extreme thermophile Methanopyrus kandleri (1991)
    Springer
    Archives of microbiology 155 (1991), S. 593-600 
    Details
    ISSN: 1432-072X
    Keywords: Methanogenic bacteria ; Methanopyrus ; Hyperthermophiles ; Thermostability ; Tetrahydromethanopterin ; Coenzyme F420
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Methanopyrus kandleri belongs to a novel group of abyssal methanogenic archaebacteria that can grow at 110°C on H2 and CO2 and that shows no close phylogenetic relationship to any methanogens known so far. N 5 N 10 -Methylenetetrahydromethanopterin reductase, an enzyme involved in methanogenesis from CO2, was purified from this hyperthermophile. The apparent molecular mass of the native enzyme was found to be 300 kDa. Sodium dodecylsulfate/polyacrylamide gel electrophoresis revealed the presence of only one polypeptide of apparent molecular mass 38 kDa. The ultraviolet/visible spectrum of the enzyme was almost identical to that of albumin indicating the absence of a chromophoric prosthetic group. The reductase was specific for reduced coenzyme F420 as electron donor; NADH, NADPH or reduced dyes could not substitute for the 5-deazaflavin. The catalytic mechanism was found to be of the ternary complex type as deduced from initial velocity plots. V max at 65°C and pH 6.8 was 435 U/mg (kcat=275 s-1) and the K m for methylenetetrahydro-methanopterin and for reduced F420 were 6 μM and 4 μM, respectively. From Arrhenius plots an activation energy of 34 kJ/mol was determined. The Q 10 between 40°C and 90°C was 1.5. The reductase activity was found to be stimulated over 100-fold by sulfate and by phosphate. Maximal stimulation (100-fold) was observed at a sulfate concentration of 2.2 M and at a phosphate concentration of 2.5 M. Sodium-, potassium-, and ammonium salts of these anions were equally effective. Chloride, however, could not substitute for sulfate or phosphate in stimulating the enzyme activity. The thermostability of the reductase was found to be very low in the absence of salts. In their presence, however, the reductase was highly thermostable. Salt concentrations between 0.1 M and 1.5 M were required for maximal stability. Potassium salts proved more effective than ammonium salts, and the latter more effective than sodium salts in stabilizing the enzyme activity. The anion was of less importance. The N-terminal amino acid sequence of the reductase from M. kandleri was determined and compared with that of the enzyme from Methanobacterium thermoautotrophicum and Methanosarcina barkeri. Significant similarity was found.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00245355
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  • 3
    Electronic Resource
    Electronic Resource
    N 5-Methyltetrahydromethanopterin: coenzyme M methyltransferase in methanogenic archaebacteria is a membrane protein (1992)
    Springer
    Archives of microbiology 158 (1992), S. 208-217 
    Details
    ISSN: 1432-072X
    Keywords: Methyltransferase ; Membrane protein ; Corrinoids ; Methanogenic bacteria ; Archaebacteria ; Energy conservation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract An assay is described that allows the direct measurement of the enzyme activity catalyzing the transfer of the methyl group from N 5-methyltetrahydromethanopterin (CH3−H4MPT) to coenzyme M (H−S−CoM) in methanogenic archaebacteria. With this method the topology, the partial purification, and the catalytic properties of the methyltransferase in methanol- and acetate-grown Methanosarcina barkeri and in H2/CO2-grown Methanobacterium thermoautotrophicum were studied. The enzyme activity was found to be associated almost completely with the membrane fraction and to require detergents for solubilization. The transferase activity in methanol-grown M. barkeri was studied in detail. The membrane fraction exhibited a specific activity of CH3−S−CoM formation from CH3−H4MPT (apparent K m=50 μM) and H−S−CoM (apparent K m=250 μM) of approximately 0.6 μmol·min-1·mg protein-1. For activity the presence of Ti(III) citrate (apparent K m=15 μM) and of ATP (apparent K m=30 μM) were required in catalytic amounts. Ti(III) could be substituted by reduced ferredoxin. ATP could not be substituted by AMP, CTP, GTP, S-adenosylmethionine, or by ATP analogues. The membrane fraction was methylated by CH3−H4MPT in the absence of H−S−CoM. This methylation was dependent on Ti(III) and ATP. The methylated membrane fraction catalyzed the methyltransfer from CH3−H4MPT to H−S−CoM in the absence of ATP and Ti(III). Demethylation in the presence of H−S−CoM also did not require Ti(III) or ATP. Based on these findings a mechanism for the methyltransfer reaction and for the activation of the enzyme is proposed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00290817
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  • 4
    Electronic Resource
    Electronic Resource
    Function of methanofuran, tetrahydromethanopterin, and coenzyme F420 in Archaeoglobus fulgidus (1989)
    Springer
    Archives of microbiology 152 (1989), S. 362-368 
    Details
    ISSN: 1432-072X
    Keywords: Archaebacteria ; Thermophiles ; Archaeoglobus ; Sulfate-reducing bacteria ; F420 ; Methanofuran ; Tetrahydromethanopterin ; Carbon monoxide dehydrogenase ; Acetyl-CoA/carbon monoxide dehydrogenase pathway ; Citric acid cycle
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Archaeoglobus fulgidus is an extremely thermophilic archaebacterium that can grow at the expense of lactate oxidation with sulfate to CO2 and H2S. The organism contains coenzyme F420, tetrahydromethanopterin, and methanofuran which are coenzymes previously thought to be unique for methanogenic bacteria. We report here that the bacterium contains methylenetetrahydromethanopterin: F420 oxidoreductase (20 U/mg), methenyltetrahydromethanopterin cyclohydrolase (0.9 U/mg), formyltetrahydromethanopterin: methanofuran formyltransferase (4.4 U/mg), and formylmethanofuran: benzyl viologen oxidoreductase (35 mU/mg). Besides these enzymes carbon monoxide: methyl viologen oxidoreductase (5 U/mg), pyruvate: methyl viologen oxidoreductase (0.7 U/mg), and membranebound lactate: dimethylnaphthoquinone oxidoreductase (0.1 U/mg) were found. 2-Oxoglutarate dehydrogenase, which is a key enzyme of the citric acid cycle, was not detectable. From the enzyme outfit it is concluded that in A. fulgidus lactate is oxidized to CO2 via a modified acetyl-CoA/carbon monoxide dehydrogenase pathway involving C1-intermediates otherwise only used by methanogenic bacteria.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00425174
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  • 5
    Electronic Resource
    Electronic Resource
    N5, N10-methylenetetrahydromethanopterin dehydrogenase (H2-forming) from the extreme thermophile Methanopyrus kandleri (1991)
    Springer
    Archives of microbiology 156 (1991), S. 43-48 
    Details
    ISSN: 1432-072X
    Keywords: Thermophiles ; Methanopyrus ; Methanogenic bacteria ; Archaebacteria ; Pterins ; Tetrahy-dromethanopterin ; Methylenetetrahydromethanopterin ; Coenzyme F420 ; Hydrogenase
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Methanopyrus kandleri is a novel abyssal methanogenic archaebacterium growing at 110°C on H2 and CO2. The N5, N10-methylenetetrahydromethanopterin dehydrogenase, an enzyme involved in methanogenesis from CO2 and H2, was purified from this hyperthermophile and characterized. The dehydrogenase was found to be composed of only one polypeptide of apparent molecular mass 44 kDa. The UV/Vis spectrum was similar to that of albumin. The protein catalyzed the reversible dehydrogenation of N5, N10-methylenetetra-hydromethanopterin (CH2=H4MPT) to N5, N10-methenyltetrahydromethanopterin (CH = H4MPT4) and molecular hydrogen: CH = H4MPT4 + H2. The rate of CH2=H4MPT dehydrogenation (apparent Vmax) at 65°C and pH5.8 was 1500 U/mg, the apparent Km for CH2=H4MPT was 50 μM, the Arrhenius activation energy was 52 kJ/mol, and the Q10 between 30°C and 70°C was 2.-. The specific activity increased hyperbolically with the proton concentration between pH 7 and pH 4.5. The purified dehydrogenase did not catalyze the reduction of viologen dyes, of coenzyme F420, and of pyridine nucleotides with either CH2=H4MPT or H2. For activity the CH2=H4MPT dehydrogenase required the presence of salts. Fifty percent of maximal activity was reached at salt concentrations of 100 mM, potassium phosphate, potassium chloride, and sodium chloride being almost equally effective in stimulating the enzyme activity. Cell extracts of M. kandleri did not loose CH2=H4MPT dehydrogenase activity when incubated at 90°C for 60 min. The purified enzyme, however, proved very themolabile. The N-terminal amino acid sequence of the dehydrogenase was determined and compared with that of the CH2=H4MPT dehydrogenase (H2-forming) from Methanobacterium thermoautotrophicum. Significant similarity was found.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00418186
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  • 6
    Electronic Resource
    Electronic Resource
    Methyl-coenzyme M reductase and other enzymes involved in methanogenesis from CO2 and H2 in the extreme thermophile Methanopyrus kandleri (1991)
    Springer
    Archives of microbiology 156 (1991), S. 49-55 
    Details
    ISSN: 1432-072X
    Keywords: methanogenic archaebacteria ; Methanopyrus ; Hyperthermophiles ; Methyl-coenzyme M reductase ; Coenzyme F430 ; Coenzyme F420 ; Methanofuran ; Tetrahydromethanopterin
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Methanopyrus kandleri belongs to a novel group of abyssal methanogenic archaebacteria that can grow at 110°C on H2 and CO2 and that shows no close phylogenetic relationship to any methanogen known so far. Methyl-coenzyme M reductase, the enzyme catalyzing the methane forming step in the energy metabolism of methanogens, was purified from this hyperthermophile. The yellow protein with an absorption maximum at 425 nm was found to be similar to the methyl-coenzyme M reductase from other methanogenic bacteria in that it was composed each of two α-, β- and γ-subunits and that it contained the nickel porphinoid coenzyme F430 as prosthetic group. The purified reductase was inactive. The N-terminal amino acid sequence of the γ-subunit was determined. A comparison with the N-terminal sequences of the γ-subunit of methyl-coenzyme M reductases from other methanogenic bacteria revealed a high degree of similarity. Besides methyl-coenzyme M reductase cell extracts of M. kandleri were shown to contain the following enzyme activities involved in methanogenesis from CO2 (apparent Vmax at 65°C): formylmethanofuran dehydrogenase, 0.3 U/mg protein; formyl-methanofuran: tetrahydromethanopterin formyltransferase, 13 U/mg; N 5,N10-methenyltetrahydromethanopterin cyclohydrolase, 14 U/mg; N 5,N10-methylenetetrahydromethanopterin dehydrogenase (H2-forming), 33 U/mg; N 5,N10-methylenetetrahydromethanopterin reductase (coenzyme F420 dependent), 4 U/mg; heterodisulfide reductase, 2 U/mg; coenzyme F420-reducing hydrogenase, 0.01 U/mg; and methylviologen-reducing hydrogenase, 2.5 U/mg. Apparent Km values for these enzymes and the effect of salts on their activities were determined. The coenzyme F420 present in M. kandleri was identified as coenzyme F420-2 with 2 γ-glutamyl residues.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00418187
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  • 7
    Electronic Resource
    Electronic Resource
    Acetate oxidation to CO2 via a citric acid cycle involving an ATP-citrate lyase: a mechanism for the synthesis of ATP via substrate level phosphorylation in Desulfobacter postgatei growing on acetate and sulfate (1987)
    Springer
    Archives of microbiology 148 (1987), S. 202-207 
    Details
    ISSN: 1432-072X
    Keywords: ATP-citrate lyase ; Citric acid cycle ; Acetate oxidation ; ATP synthesis via substrate level phosphorylation ; Sulfate-reducing bacteria ; Desulfobacter postgatei
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Desulfobacter postgatei is an acetate-oxidizing, sulfate-reducing bacterium that metabolizes acetate via the citric acid cycle. The organism has been reported to contain a si-citrate synthase (EC 4.1.3.7) which is activated by AMP and inorganic phosphate. It is show now, that the enzyme mediating citrate formation is an ATP-citrate lyase (EC 4.1.3.8) rather than a citrate synthase. Cell extracts (160,000xg supernatant) catalyzed the conversion of oxaloacetate (apparent K m=0.2 mM), acetyl-CoA (app. K m=0.1 mM), ADP (app. K m=0.06 mM) and phosphate (app. K m=0.7 mM) to citrate, CoA and ATP with a specific activity of 0.3 μmol·min-1·mg-1 protein. Per mol citrate formed 1 mol of ATP was generated. Cleavage of citrate (app. K m=0.05 mM; V max=1.2 μmol · min-1 · mg-1 protein) was dependent on ATP (app. K m=0.4 mM) and CoA (app. K m=0.05 mM) and yielded oxaloacetate, acetyl-CoA, ADP, and phosphate as products in a stoichiometry of citrate:CoA:oxaloacetate:ADP=1:1:1:1. The use of an ATP-citrate lyase in the citric acid cycle enables D. postgatei to couple the oxidation of acetate to 2 CO2 with the net synthesis of ATP via substrate level phosphorylation.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00414812
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  • 8
    Electronic Resource
    Electronic Resource
    N 5,N 10-Methenyltetrahydromethanopterin cyclohydrolase from the extreme thermophile Methanopyrus kandleri: increase of catalytic efficiency (kcat/K M) and thermostability in the presence of salts (1991)
    Springer
    Archives of microbiology 156 (1991), S. 517-524 
    Details
    ISSN: 1432-072X
    Keywords: Methanogenic bacteria ; Archaebacteria ; Methanopyrus ; Hyperthermophiles ; Thermostability ; Tetrahydromethanopterin
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The activity of purified N 5,N 10-methenyltetrahydromethanopterin cyclohydrolase from Methanopyrus kandleri was found to increase up to 200-fold when potassium phosphate was added in high concentrations (1.5 M) to the assay. A 200-fold stimulation was also observed with sodium phosphate (1 M) and sodium sulfate (1 M) whereas stimulation by potassium sulfate (0.8 M), ammonium sulfate (1.5 M), potassium chloride (2.5 M), and sodium chloride (2 M) was maximal 100-fold. A detailed kinetic analysis of the effect of potassium phosphate revealed that this salt exerted its stimulatory effect by decreasing the K m for N 5,N 10-methenyltetrahydromethanopterin from 2 mM to 40 μM and by increasing the V max from 2000 U/mg (kcat=1385 s-1) to 13300 U/mg (kcat=9200 s-1). Besides increasing the catalytic efficiency (kcat/K m) salts were found to protect the cyclohydrolase from heat inactivation. For maximal thermostability much lower concentrations (0.1 M) of salts were required than for maximal activity.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00245402
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  • 9
    Electronic Resource
    Electronic Resource
    N 5,N 10-Methylenetetrahydromethanopterin reductase (coenzyme F420-dependent) and formylmethanofuran dehydrogenase from the hyperthermophile Archaeoglobus fulgidus (1991)
    Springer
    Archives of microbiology 156 (1991), S. 427-434 
    Details
    ISSN: 1432-072X
    Keywords: Sulfate-reducing archaebacteria ; Hyperthermophilic bacteria ; Archaeglobus fulgidus ; Tetrahydromethanopterin ; Methanofuran ; Coenzyme F420 ; Thermostable enzymes
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Methylene-H4MPT reductase was found to be present in Archaeoglobus fulgidus in a specific activity of 1 U/mg. The reductase was purified 410-fold. The native enzyme showed an apparent molecular mass of approximately 200 kDa. Sodium dodecylsulfate/polyacrylamide gel electrophoresis revealed the presence of only 1 polypeptide of apparent molecular mass 35 kDa. The ultraviolet/visible spectrum of the reductase was almost identical to that of albumin indicating the absence of a chromophoric prosthetic group. The reductase was dependent on reduced coenzyme F420 as electron donor. Neither NADH, NADPH, nor reduced viologen dyes could substitute for the reduced deazaflavin. From reciprocal plots, which showed an intersecting patter, a K m for methylene-H4MPT of 16 μM, a K m for F420H2 of 4 μM, and a V max of 450 U/mg (Kcat=265 s-1) were obtained. The enzyme was found to be rapidly inactivated when incubated at 80°C in 100 mM Tris/HCl pH 7. The rate of inactivation, however, decreased to essentially zero in the presence of either F420 (0.2 mM), methylene-H4MPT (0.2 mM), albumin (1 mg/ml), or KCl (0.5 M). The N-terminal amino acid sequence was determined and found to be similar to that of methylene-H4MPT reductase (F420-dependent) from the methanogens Methanobacterium thermoautotrophicum, Methanosarcina barkeri, and Methanopyrus kandleri. The purification and some properties of formylmethanofuran dehydrogenase from A. fulgidus are also described.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00248722
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  • 10
    Electronic Resource
    Electronic Resource
    N 5,N 10-Methenyltetrahydromethanopterin cyclohydrolase from the extremely thermophilic sulfate reducing Archaeoglobus fulgidus: comparison of its properties with those of the cyclohydrolase from the extremely thermophilic Methanopyrus kandleri (1993)
    Springer
    Archives of microbiology 159 (1993), S. 213-219 
    Details
    ISSN: 1432-072X
    Keywords: Archaea ; Methanogenic bacteria ; Hyperthermophiles ; Sulfate reducers ; Methanobacterium thermoautotrophicum ; Methanosarcina barkeri ; Tetrahydromethanopterin
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Archaeoglobus fulgidus and Methanopyrus kandleri are both extremely thermophilic Archaea with a growth temperature optimum at 83°C and 98°C, respectively. Both Archaea contain an active N 5,N 10-methenyltetrahydromethanopterin cyclohydrolase. The enzyme from M. kandleri has recently been characterized. We describe here the purification and properties of the enzyme from A. fulgidus. The cyclohydrolase from A. fulgidus was purified 180-fold to apparent homogeneity and its properties were compared with those recently published for the cyclohydrolase from M. kandleri. The two cytoplasmic enzymes were found to have very similar molecular and catalytic properties. They differed, however, significantly with respect of the effect of K2HPO4 and of other salts on the activity and the stability. The cyclohydrolase from A. fulgidus required relatively high concentrations of K2HPO4 (1 M) for optimal thermostability at 90°C but did not require salts for activity. Vice versa, the enzyme from M. kandleri was dependent on high K2HPO4 concentrations (1.5 M) for optimal activity but not for thermostability. Thus the activity and structural stability of the two thermophilic enzymes depend in a completely different way on the concentration of inorganic salts. The molecular basis for these differences are discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00248474
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