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Query: EC:6.2.1.1 (ACS)
 78,556 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

In Pseudomonas AM1, conversion of 3-hydroxybutyrate to acetyl-CoA is mediated by an inducible 3-hydroxybutyrate dehydrogenase, an acetoacetate: succinate coenzyme A transferase (specific for succinyl-CoA) and an inducible beta-ketothiolase. Ethanol is oxidized to acetate by the same enzymes as are involved in methanol oxidation to formate. An inducible acetyl-CoA synthetase has been partially purified and characterized; it is essential for growth only on ethanol, malonate and acetate plus glyoxylate, as shown by the growth characteristics of a mutant (ICT54) lacking this enzyme. Free acetate is not involved in the assimilation of acetyl-CoA, and hydroxypyruvate reductase is not involved in the oxidation of acetyl-CoA to glyoxylate during growth on 3-hydroxybutyrate. A mutant (ICT51), lacking 'malate synthase' activity has been isolated and its characteristics indicate that this activity is normally essential for growth, of Pseudomonas AM1 on ethanol, malonate and 3-hydroxybutyrate, but not for growth on other substrates such as pyruvate, succinate and C1 compounds. The growth properties of a revertant (ICT51R) and of a mutant lacking malyl-CoA lyase (PCT57) indicate that an alternative route must exist for assimilation of compounds metabolized exclusively by way of acetyl-CoA.
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PMID:Acetyl-CoA production and utilization during growth of the facultative methylotroph Pseudomonas AM1 on ethanol, malonate and 3-hydroxybutyrate. 0 84

The acetate activating system of Acetobacter aceti has been studied. The enzyme responsible, acetyl-CoA synthetase, has been purified about 500-fold from crude cell extracts and was approximately 85% pure as judged by polyacrylamide gel electrophoresis in sodium dodecyl sulphate. The purified enzyme showed optimal activity at pH 7.6 in both Tris-HCL and potassium phosphate buffers. In its purest form, the enzyme was stable at 4 degrees-C but denatured upon freezing. The Km values for CoA, ATP and acetate were found to be 0.104 mM, 0.36 mM and 0.25 mM respectively; propionate and acrylate were also activated by the enzyme but not butyrate, isobutyrate or valerate. GTP, UTP, CTP and ADP could not replace ATP in the reaction, and cysteine or pantetheine failed to replace CoA. The cationic requirements were studied and of the divalent cations tested, only Mn2+ could significantly replace Mg2+ in the reaction; K+ and NH4+ stimulated enzyme activity but inhibited at high concentrations; Na+ was a poor activator, but did not inhibit at higher concentrations. The effect of a number of glucose and other metabolites on enzyme activity has been tested.
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PMID:Characterization of the acetyl-CoA synthetase of Acetobacter aceti. 1

Under anaerobic conditions, cells of Entamoeba histolytica grown with bacteria produce H2 and acetate while cells grown axenically produce neither. Aerobically, acetate is produced and O2 is consumed by amebae from either type of cells. Centrifuged extracts, 2.4 x 106 x g x min, from both types of cells contain pyruvate synthase (EC 1.2.7.1) and an acetate thiokinase which, together, form a system capable of converting pyruvate to acetate. Pyruvate synthase catalyzes the reaction: pyruvate + CoA leads to CO2 + acetyl-CoA + 2E. Electron acceptors which function with this enzyme are FAD, FMN, riboflavin, ferredoxin, and methyl viologen, but not NAD or NADP. The amebal acetate thiokinase catalyzes the reaction acetyl-CoA + ADP + Pi leads to acetate + ATP + CoA. For this apparently new enzyme we suggest the trivial name acetyl-CoA-synthetase (ADP-forming). Extracts from axenic amebae do not contain hydrogenase, but extracts from cells grown with bacteria do. It is postulated that in bacteria-grown amebae electrons generated at the pyruvate synthase step are utilized anaerobically to produce H2 via the hydrogenase and that the acetyl-CoA is converted to acetate in an energy-conserving step catalyzed by amebal acetyl-CoA synthetase. Aerobically, cells grown under either regimen may utilize the energy-conserving pyruvate-to-acetate pathway since O2 then serves as the ultimate electron acceptor.
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PMID:An energy-conserving pyruvate-to-acetate pathway in Entamoeba histolytica. Pyruvate synthase and a new acetate thiokinase. 1 76

Mutants of Escherichia coli K12 have been isolated that grow on media containing pyruvate of proline as sole carbon sources despite the presence of 10 or 50 mM-sodium fluoroacetate. Such mutants lack either acetate kinase [ATP: acetate phosphotransferase; EC 2.7.2.1] or phosphotransacetylase [acetyl-CoA: orthophosphate acetyltransferase; EC 2.3.1.8] activity. Unlike wild-type E. coli, phosphotransacetylase mutants do not excrete acetate when growing aerobically or anaerobically on glucose; their anaerobic growth on this sugar is slow. The genes that specify acetate kinase (ack) and phosphotransacetylase (pta) activities are cotransducible with each other and with purF and are thus located at about min 50 on the E. coli linkage map. Although Pta- and Ack- mutants are greatly impaired in their growth on acetate, they incorporate [2-14C]acetate added to cultures growing on glycerol, but not on glucose. An inducible acetyl-CoA synthetase [acetate: CoA ligase (AMP-forming); EC 6.2.1.1] effects this uptake of acetate.
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PMID:The enzymic interconversion of acetate and acetyl-coenzyme A in Escherichia coli. 2 41

Formation of acetyl-CoA through acetyl-CoA synthetase (forward reaction) and through choline acyltransferase (backward reaction) was investigated in tissue extract from the electric organ of Torpedo marmorata. When the tissue extract was submitted to gel filtration on Sephadex G-25, the formation of acetyl-CoA by acetyl-CoA synthetase appeared fully dependent on ATP and CoA and partially dependent on acetate (an endogenous supply of acetate is discussed). Choline acetyltransferase was a potent source of acetyl-CoA, only requiring acetylcholine and CoA, and was much more efficient than acetyl-CoA synthetase for concentrations of acetylcholine likely to be present in nerve endings.
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PMID:Biosynthesis of acetyl-coenzyme A in the electric organ of Torpedo marmorata in relation to acetylcholine metabolism. 2 1

The synthesis of a new coenzyme A analogue, N6-[N-(6-aminohexyl)carbamoylmethyl]-CoA, suitable for immobilisation through its terminal amino group to support matrices, is described. The synthetic route starts with bis(CoA) and involves the following steps: alkylation with iodoacetic acid and rearrangement yielding bis(N6-carboxymethyl-CoA), elongation of the carboxymethyl terminal with 1,6-diaminohexane using carbodiimide to yield bis(N6-[N-(6-aminohexyl)-carbamoylmethyl]-CoA) and finally the splitting of this bis[CoA analogue) through reduction with dithiothreitol to give the final product in approximately 10% overall yield. This CoA analogue showed 'coenzymic activity' with the enzymes acetyl-CoA synthetase, phosphotransacetylase and succinic thiokinase. Covalent binding of the CoA analogue to Sepharose 4B was normally carried out using its S-(5-thio-2-nitrobenzoic acid) derivative as this allows a convenient way for determining the amount of ligand coupled, based on the amount of 5-thio-2-nitrobenzoic acid liberated from the gel after reduction with dithiothreitol. After covalent binding of the CoA analogue to water-soluble activated dextran 70, the analogue was recycled while present in an ultrafiltration cell using the enzymes phosphotransacetylase and citrate synthase. The reaction was followed by measuring the citrate formed on addition of acetylphosphate and oxaloacetate. In affinity chromatographic studies it was shown that the CoA-Sepharose preparation could bind the CoA-dependent enzymes citrate synthase and succinic thiokinase and these could be biospecifically eluted using soluble CoA.
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PMID:N6-[N-(6-Aminohexyl)carbamoylmethyl]-coenzyme A. Synthesis and application in affinity chromatography and as an immobilized active coenzyme. 57 88

In order to assess the extent to which metabolism within the sheep placenta may influence the transfer of metabolites between mother and foetus at different stages of gestation the activities of enzymes concerned with some aspects of carbohydrate, amino acid and keton body metabolism were determined in placental cotyledons resected from ewes during the last three months of pregnancy. The activities of pyruvate kinase (EC 2.7.1.40), lactate dehydrogenase (EC 1.1.1.27), malate dehydrogenase (EC 1.1.1.37), ATP citrate (pro-3S)-lyase (EC 4.1.3.8), citrate (si)-synthase (EC 4.1.3.7), acetyl-CoA synthetase (EC 6.2.1.1), acetyl-CoA acetyltransferase (EC 2.3.1.9) and 3-keto acid CoA-transferase (EC 2.8.3.5) per gram wet weight cotyledon do not change during the period studied. The activities of alanine aminotransferase (EC 2.6.1.2), aspartate aminotransferase (EC 2.6.1.1), isocitrate dehydrogenase (NADP+) (EC 1.1.1.42), ornithine-oxoacid aminotransferase (EC 2.6.1.13) and 3-hydroxybutyrate dehydrogenase (EC 1.1.1.30) show an increase in activity between the third and fourth months of pregnancy whilst the activities of arginase (EC 3.5.3.1) and possibly pyruvate carboxylase (EC 6.4.1.1) show an increase in activity between the fourth and final months of pregnancy. Ornithine decarboxylase (EC 4.1.1.17) activity declines to one tenth of its activity during this later period. The absence of detectable activities of phosphoenolpyruvate carboxykinase (EC 4.1.1.32) and ornithine carbamoyltransferase (EC 2.1.3.3) indicate that gluconeogenesis and urea synthesis from ammonia do not occur in the sheep placenta. It appears that the ability of the placenta to metabolise several substrates is achieved by the time the placenta reaches its maximum size at approximately 90 days.
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PMID:Enzyme activities in the sheep placenta during the last three months of pregnancy. 84 73

A DNA fragment of Saccharomyces cerevisiae with high homology to the acetyl-coenzyme A (acetyl-CoA) synthetase genes of Aspergillus nidulans and Neurospora crassa has been cloned, sequenced and mapped to chromosome I. It contains an open reading frame of 2139 nucleotides, encoding a predicted gene product of 79.2 kDa. In contrast to its ascomycete homologs, there are no introns in the coding sequence. The first ATG codon of the open reading frame is in an unusual context for a translational start site, while the next ATG, 24 codons downstream, is in a more conventional context. Possible implications of two alternative translational start sites for the cellular localization of the enzyme are discussed. A stable mutant of this gene, obtained by the gene disruption technique, had the same low basal activity of acetyl-CoA synthetase as wild-type cells when grown on glucose but completely lacked the strong increase in activity upon entering the stationary phase, providing direct proof that the gene encodes an inducible acetyl-CoA synthetase (ACS1) of yeast. As expected, the mutant was unable to grow on acetate as sole carbon source. Nevertheless, it showed normal induction of isocitrate lyase on acetate media, indicating that activity of acetyl-CoA synthetase is dispensable for induction of the glyoxylate cycle in S. cerevisiae. Surprisingly, disruption of the ACS1 gene did not affect growth on media containing ethanol as the sole carbon source, demonstrating that there are alternative pathways leading to acetyl-CoA under these conditions.
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PMID:Cloning and disruption of a gene required for growth on acetate but not on ethanol: the acetyl-coenzyme A synthetase gene of Saccharomyces cerevisiae. 136 52

The benzoyl-CoA ligase from an anaerobic syntrophic culture was purified to homogeneity. It had a molecular mass of around 420 kDa and consisted of seven or eight subunits of 58 kDa. The temperature optimum was 37-40 degrees C, the optimum pH around 8.0 and optimal activity required 50-100 mM TRIS-HCl buffer, pH 8.0 and 3-7 mM MgCl2; MgCl2 in excess of 10 mM was inhibitory. The activation energy for benzoate was 11.3 kcal/mol. Although growth occurred only with benzoate as a carbon source, the benzoyl-coenzyme A (CoA) ligase formed benzoyl-CoA esters with benzoate, 2-, 3- and 4-fluorobenzoate, picolinate, nicotinate and isonicotinate. Acetate was activated to acetyl-CoA by an acetyl-CoA synthetase. The Km values for benzoate, 2-, 3- and 4-fluorobenzoate were 0.04, 0.28, 1.48 and 0.32 mM, the Vmax values 1.05, 1.0, 0.7 and 0.98 units (U)/mg, respectively. For reduced CoA (CoA-SH) a Km of 0.07 mM and a Vmax of 1.05 U/mg and for ATP a Km of 0.16 mM and a Vmax of 1.08 U/mg was determined. Benzoate activation was inhibited by more than 6 mM ATP, presumably by pyrophosphate generation from ATP. The inhibition constant (Ki) for pyrophosphate was 5.7 mM. No homology of the N-terminal amino acid sequence with that of a 2-aminobenzoyl-CoA ligase of a denitrifying Pseudomonas sp. was found.
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PMID:Purification and characterization of benzoyl-CoA ligase from a syntrophic, benzoate-degrading, anaerobic mixed culture. 136 92

An account is presented of the recent discovery of a pathway of growth by bacteria in which CO or CO2 and H2 are sources of carbon and energy. The Calvin cycle and subsequently other cycles were discovered in the 1950s, and in each the initial reaction of CO2 involved adding CO2 to an organic compound formed during the cyclic pathway (for example, CO2 and ribulose diphosphate). Studies were initiated in the 1950s with the thermophylic anaerobic organism Clostridium thermoaceticum, which Barker and Kamen had found fixed CO2 in both carbons of acetate during fermentation of glucose. The pathway of acetyl-CoA biosynthesis differs from all others in that two CO2 are combined with coenzyme A (CoASH) forming acetyl CoA, which then serves as the source of carbon for growth. This mechanism is designated the acetyl CoA pathway and some have called it the Wood pathway. A unique feature is the role of the enzyme carbon monoxide dehydrogenase (CODH), which catalyzes the conversion of CoASH, CO, and a methyl group to acetyl CoA, the final step of the pathway. The pathway involves the reduction of CO2 to formate, which then combines with tetrahydrofolate (THF) to form formyl THF. It in turn is reduced to CH3-THF. The methyl is then transferred to the cobalt on a corrinoid-containing enzyme. From there the methyl is transferred to CODH, and CO and CoASH bind with the enzyme at separate sites. Acetyl CoA is then synthesized. CODH would more properly be called carbon monoxide dehydrogenase-acetyl CoA synthase as it catalyzes oxidation of CO to CO2 and the synthesis of acetyl CoA. The solution of the mechanism of this pathway required more than 30 years, in part because the intermediate compounds are bound to enzymes, the enzymes are extremely sensitive to O2 and must be isolated under strictly anerobic conditions, and the role of a corrinoid and CODH was unprecedented. It is now apparent that this pathway occurs (perhaps with some modification) in many bacteria including the methane and sulfur bacteria. In some humans this pathway is catalyzed by the bacteria of the gut and acetate is produced rather than methane; it is calculated that 2.3 x 10(6) metric tons of acetate are formed daily from CO2. A similar synthesis occurs in the hind gut of termites. It is becoming apparent that the acetyl CoA pathway plays a significant role in the carbon cycle.(ABSTRACT TRUNCATED AT 400 WORDS)
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PMID:Life with CO or CO2 and H2 as a source of carbon and energy. 190 Jul 93


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