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41.
42.
Is coenzyme M bound to factor F430 in methanogenic bacteria? Experiments with Methanobrevibacter ruminantium 总被引:3,自引:0,他引:3
Coenzyme M (2-mercaptoethane sulfonic acid) and factor F430 (a nickel porphinoid) are coenzymes found in methanogenic bacteria. Recently it has been proposed that in these bacteria a coenzyme MF430 also exists which plays a key role in methane formation and in which coenzyme M and F430 are bound to each other. To test this hypothesis Methanobrevibacter ruminantium, which requires coenzyme M as a vitamin, was grown in the presence of [2-14C]CoMSH. F430 and 'CoM' (mixture of CoMSH and its disulfides) were quantitatively extracted from these cells and from partially purified methyl-CoM reductase using various methods. The extracts were chromatographed on cellulose or Sephadex G-10. Under all conditions factor F430 and 'CoM' were completely (greater than 99%) separated. There was no indication for the existence of a protein-free F430 species containing covalently bound coenzyme M in Mb. ruminantium. The results support the structure previously assigned to coenzyme F430. 相似文献
43.
Norbert A. Gebhardt Rudolf K. Thauer Dietmar Linder Paul-M. Kaulfers Norbert Pfennig 《Archives of microbiology》1985,141(4):392-398
The strict anaerobe Desulfuromonas acetoxidans can oxidize acetate to CO2 with elemental sulfur as electron acceptor. 14C-labelling experiments and enzyme studies are described revealing that acetate oxidation proceeds via the citric acid cycle with the synthesis of oxaloacetate from acetate and 2 CO2 via pyruvate as anaplerotic reaction. An oxidation of acetate via one carbon unit intermediates as proposed for anaerobic bacteria fermenting acetate to 2 CO2 and 4 H2 was excluded.Dedicated to Professor Dr. Gerhart Drews on the occasion of his 60th birthday 相似文献
44.
From our previous studies on the mechanism of methane formation from acetate it was known that cell extracts of acetate-grown Methanosarcina barkeri (100 000 × g supernatant) catalyze the conversion of acetyl-CoA plus tetrahydromethanopterin (=H4MPT) to methyl-H4MPT, CoA, CO2 and presumably H2. We report here that these extracts, in the absence of H4MPT, mediated an isotope exchange between CO2 ([S]0.5 v=0.2% in the gas phase) and the carbonyl group of acetyl-CoA at almost the same specific rate as the above conversion (10 nmol · min–1 · mg protein–1). Both the exchange and the formation of methyl-H4MPT were inhibited by N2O, suggesting that a corrinoid could be the primary methyl group acceptor in the acetyl-CoA C-C-cleavage reaction. Both activities were dependent on the presence of H2 (E0=–414 mV). Ti(III)citrate (E0=–480 mV) was found to substitute for H2, indicating a reductive activation of the system. In the presence of Ti(III)citrate it was shown that the formation of CO2 from the carbonyl group of acetyl-CoA is associated with a 1:1 stoichiometric generation of H2. Free CO, a possible intermediate in CO2 and H2 formation, was not detected.Non-standard abbreviations AcCoA
acetyl-CoA
- acetyl-P
acetyl phosphate
- OH-B12
hydroxocobalamin
- H-S-CoM
coenzyme M = 2-mercaptoethanesulfonate
- CH3-S-CoM
methyl-coenzyme M = 2-(methylthio)ethanesulfonate
- H-S-HTP
N-7-mercaptoheptanoylthreonine phosphate
- HTP-S-S-HTP
disulfide of H-S-HTP
- CoM-S-S-HTP
disulfide of H-S-CoM and H-S-HTP
- H4MPT
tetrahydromethanopterin
- CH3-H4MPT
N5-methyl-H4MPT
- DTT
dithiothreitol
- MOPS
morpholinopropane sulfonic acid 相似文献
45.
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.Abbreviations HPLC
high performance liquid chromatography
- acetyl-P
acetyl phosphate 相似文献
46.
The active species of CO2 , i.e. CO2 or HCO
3
–
–(H2CO3) utilized by enzymes catalyzing ferredoxin-linked carboxylation reactions was determined. The enzyme investigated was pyruvate synthase from Clostridium pasteurianum (EC 1.2.7.1; Pyruvate: ferredoxin oxidoreductase). Data were obtained which were compatible with those expected if CO2 is the active species.The dissociation constant (K
S) of the enzyme-CO2 complex was measured. At pH 7.2 K
Sfor CO2 of pyruvate synthase was found to be approximately 5 mM.Abbreviations Fd
ferredoxin
No distinctions are made between CO2, H2CO3, HCO
3
–
and CO
3
=
when the symbol CO2 is used. 相似文献
47.
48.
49.
The oxidation of succinate with elemental sulphur in Desulfuromonas acetoxidans was investigated using a membrane preparation of this bacterium. The following results were obtained:
- The preparation catalyzed the oxidation of succinate with sulphur and NAD. These reactions were dependent on ATP and were abolished by the presence of protonophores or dicyclohexylcarbodiimide (DCCD).
- The membrane preparation also catalyzed the reduction of fumarate with H2S or with NADH. These activities were not dependent on ATP and were not affected by protonophores or DCCD.
- By extraction-reincorporation experiments it could be shown that menaquinone is involved in electron transport between H2S and fumarate and between NADH and fumarate.
- The membrane fraction catalyzed the reduction of the water-soluble menaquinone-analogue dimethylnaphthoquinone (DMN) by succinate, H2S, or NADH, and the oxidation of DMNH2 by fumarate. These activities were not dependent on the presence of menaquinone and were not influenced by ATP.
- The activities involving succinate oxidation or fumarate reduction were similarly sensitive to 2(n-nonyl)-4-hydroxyquinoline-N-oxide, while H2S and NADH oxidation by DMN were not affected by the inhibitor.
50.
Rolf Schauder Bernhard Eikmanns Rudolf K. Thauer Fritz Widdel Georg Fuchs 《Archives of microbiology》1986,145(2):162-172
In several sulfate-reducing bacteria capable of complete oxidation of acetate (or acetyl CoA), the citric acid cycle is not operative. No 2-oxoglutarate dehydrogenase activity was found in these organisms, and the labelling pattern of oxaloacetate excludes its synthesis via 2-oxo-glutarate. These sulfate-reducers contained, however, high activities of the enzymes carbon monoxide dehydrogenase and formate dehydrogenase and catalyzed an isotope exchange between CO2 and the carboxyl group of acetate (or acetyl CoA), showing a direct C-C-cleavage of activated acetic acid. These findings suggest that in the investigated sulfate-reducers acetate is oxidized to CO2 via C1 intermediates. The proposed pathway provides a possible explanation for the reported different fluoroacetate sensitivity of acetate oxidation by anaerobic bacteria, for mini-methane formation, as well as for the postulated anaerobic methane oxidation by special sulfate-reducers. 相似文献