Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: EC:6.2.1.13 (acetyl-CoA synthetase)
 451 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

1. A method for measuring small amounts of acetyl-CoA synthesized in subcellular fractions of the brain from pyruvate and released from particles into the incubation medium has been developed by using placental choline acetyltransferase and choline in the incubation medium to transform acetyl-CoA into acetylcholine. Acetylcholine is measured by biological assay. Optimum conditions of incubation are described. 2. With fresh mitochondria, a decrease of acetyl-CoA output into the medium is observed in the presence of ATP or ADP, and an increase in the presence of calcium chloride or 2,4-dinitrophenol. Fluorocitrate and malonate have little or no effect. 3. After the mitochondria had been treated with ether, the release of acetyl-CoA into the medium is much larger; presumably, nearly all acetyl-CoA synthesized is then released and transformed into acetylcholine under the conditions used. The release of acetyl-CoA is diminished in the presence of Krebs-cycle intermediates and ADP. 4. Of all subcellular fractions, the highest acetyl-CoA production from pyruvate is found in the crude mitochondria; rates up to 51 mumoles of acetyl-CoA/g. of original tissue/hr. are observed in ether-treated samples. 5. The activities of acetyl-CoA synthetase and ATP citrate lyase found in homogenates and nerve-ending fractions of brain tissue are considerably lower than those of pyruvate oxidase complex and choline acetyltransferase. 6. The bearing of some of the findings on the question of the source of acetyl radicals for the synthesis of acetylcholine in vivo is discussed.
 ...
PMID:The use of choline acetyltransferase for measuring the synthesis of acetyl-coenzyme A and its release from brain mitochondria. 604 20

The metabolic importance of pyruvate oxidase (PoxB), which converts pyruvate directly to acetate and CO(2), was assessed using an isogenic set of genetically engineered strains of Escherichia coli. In a strain lacking the pyruvate dehydrogenase complex (PDHC), PoxB supported acetate-independent aerobic growth when the poxB gene was expressed constitutively or from the IPTG-inducible tac promoter. Using aerobic glucose-limited chemostat cultures of PDH-null strains, it was found that steady-states could be maintained at a low dilution rate (0.05 h(-1)) when PoxB is expressed from its natural promoter, but not at higher dilution rates (up to at least 0.25 h(-1)) unless expressed constitutively or from the tac promoter. The poor complementation of PDH-deficient strains by poxB plasmids was attributed to several factors including the stationary-phase-dependent regulation of the natural poxB promoter and deleterious effects of the multicopy plasmids. As a consequence of replacing the PDH complex by PoxB, the growth rate (mu(max)), growth yield (Y(max)) and the carbon conversion efficiency (flux to biomass) were lowered by 33%, 9-25% and 29-39% (respectively), indicating that more carbon has to be oxidized to CO(2) for energy generation. Extra energy is needed to convert PoxB-derived acetate to acetyl-CoA for further metabolism and enzyme analysis indicated that acetyl-CoA synthetase is induced for this purpose. In similar experiments with a PoxB-null strain it was shown that PoxB normally makes a significant contribution to the aerobic growth efficiency of E. coli. In glucose minimal medium, the respective growth rates (mu(max)), growth yields (Y(max)) and carbon conversion efficiencies were 16%, 14% and 24% lower than the parental values, and correspondingly more carbon was fluxed to CO(2) for energy generation. It was concluded that PoxB is used preferentially at low growth rates and that E. coli benefits from being able to convert pyruvate to acetyl-CoA by a seemingly wasteful route via acetate.
 ...
PMID:Pyruvate oxidase contributes to the aerobic growth efficiency of Escherichia coli. 1139 Jun 79

Acetate accumulation is a common problem observed in aerobic high cell density cultures of Escherichia coli. It has been hypothesized in previous reports that the glyoxylate shunt is active in E. coli BL21, the low acetate producer, and inactive in E. coli JM109, the high acetate producer. This hypothesis was further strengthened by incorporating 13C from uniformly labeled glucose into TCA cycle intermediates. Using northern blot analyses, the current report demonstrates that the reason for the inactivity of the glyoxylate pathway in E. coli JM109 is the no apparent transcription of isocitrate lyase (aceA) and malate synthase (aceB), and transcription of the isocitrate lyase repressor (iclR). The reverse is seen in E. coli BL21 where the glyoxylate pathway is active due to constitutive transcription of aceA and aceB and no transcription of the iclR. In addition, there is a difference between the two strains in the transcription of the acetyl-CoA synthetase (acs), phosphotransacetylase-acetate kinase (pta-ackA) pathway, and pyruvate oxidase (poxB), pathway. The transcript of acs is higher in E. coli BL21 and lower in the E. coli JM109, while the reverse is true for poxB transcription.
 ...
PMID:Transcription levels of key metabolic genes are the cause for different glucose utilization pathways in E. coli B (BL21) and E. coli K (JM109). 1506 11

In a series of previous reports it was established by implementing metabolic flux, NMR/MS, and Northern blot analysis that the glyoxylate shunt, the TCA cycle, and acetate uptake by acetyl-CoA synthetase are more active in Escherichia coli BL21 than in Escherichia coli JM109. These differences were accepted as the reason for the differences in the glucose metabolism and acetate excretion of these two strains. Examination of the bacterial metabolism by microarrays and time course Northern blot showed that in addition to the glyoxylate shunt, the TCA cycle and the acetate uptake, other metabolic pathways are active differently in the two strains. These are gluconeogenesis, sfcA shunt, ppc shunt, glycogen biosynthesis, and fatty acid degradation. It was found that in E. coli JM109, acetate is produced by pyruvate oxidase (poxB) using pyruvate as a substrate rather than by phosphotransacetylase-acetate kinase (Pta-AckA) system which uses acetyl-CoA. The inactivation of the gluconeogenesis enzyme phosphoenolpyruvate synthetase (ppsA), the activation of the anaplerotic sfcA shunt, and low and stable pyruvate dehydrogenase (aceE, aceF) cause pyruvate accumulation which is converted to acetate by pyruvate oxidase B. The behavior of the ppsA, acs, and aceBAK in JM109 was dependent on the glucose supply strategy. When the glucose concentration was high, no transcription of these genes was observed and acetate concentration increased, but at low glucose concentrations these genes were expressed and the acetate concentration decreased. It is possible that there is a major regulatory molecule that controls not only ppsA and aceBAK but also acs. The gluconeogenesis pathway (fbp, pckA, and ppsA) which leads to glycogen accumulation is constitutively active in E. coli BL21 regardless of glucose feeding strategy.
 ...
PMID:Glucose metabolism at high density growth of E. coli B and E. coli K: differences in metabolic pathways are responsible for efficient glucose utilization in E. coli B as determined by microarrays and Northern blot analyses. 1580 47

The lipoamide dehydrogenase (LPD) encoded by lpdA gene is a component of the pyruvate dehydrogenase complex (PDHc), alpha-ketoglutarate dehydrogenase (AKGDH) and the glycine cleavage multi-enzyme (GCV) systems. In the present study, cell growth characteristics, enzyme activities and intracellular metabolite concentrations were compared between the parent strain Escherichia coli BW25113 and its lpdA knockout mutant in batch and continuous cultures. The lpdA knockout mutant produced significantly more pyruvate and L-glutamate under aerobiosis. Some D-lactate and succinate also accumulated in the culture broth. Based on the investigation of enzyme activities and intracellular metabolite concentrations, acetyl-CoA was considered to be formed by the combined reactions through pyruvate oxidase (PoxB), acetyl-CoA synthetase (Acs) and acetate kinase (Ack)-phosphoacetyltransferase (Pta) in the lpdA mutant. The effect of the lpdA gene knockout on the intracellular metabolic flux distributions was investigated based on 1H-13C NMR spectra and GC-MS signals obtained from 13C-labeling experiment using the mixture of [U-13C] glucose, [1-13C] glucose, and naturally labeled glucose. Flux analysis of the lpdA mutant indicated that the Entner-Doudoroff (ED) pathway and the glyoxylate shunt were activated. The fluxes through glycolysis and oxidative pentose phosphate (PP) pathway (except for the flux through glucose-6-phosphate dehydrogenase) were slightly downregulated. The TCA cycle was also downregulated in the mutant strain. On the other hand, the fluxes through the anaplerotic reactions of PEP carboxylase, PEP carboxykinase and malic enzyme were upregulated, which were consistent with the results of enzyme activities. Furthermore, the influence of the poxB gene knockout on the growth of E. coli was also studied because of its similar function to PDHc which connects the glycolysis to the TCA cycle. Under aerobiosis, a comparison of lpdA mutant and poxB mutant indicated that PDHc is the main enzyme which catalyzes the reaction from pyruvate to acetyl-CoA in the parent strain, while PoxB plays a very important role in the PDHc-deficient strain.
 ...
PMID:Effect of lpdA gene knockout on the metabolism in Escherichia coli based on enzyme activities, intracellular metabolite concentrations and metabolic flux analysis by 13C-labeling experiments. 1631 Feb 73

Single-gene mutants with extended lifespan have been described in several model organisms. We performed a genome-wide screen for long-lived mutants in Escherichia coli, which revealed strains lacking tricarboxylic acid (TCA)-cycle-related genes that exhibit longer stationary-phase survival and increased resistance to heat stress compared to wild-type. Extended lifespan in the sdhA mutant, lacking subunit A of succinate dehydrogenase, is associated with the reduced production of superoxide and increased stress resistance. On the other hand, the longer lifespan of the lipoic acid synthase mutant (lipA) is associated with reduced oxygen consumption and requires the acetate-producing enzyme pyruvate oxidase, as well as acetyl-CoA synthetase, the enzyme that converts extracellular acetate to acetyl-CoA. The hypoxia-inducible transcription factor ArcA, acting independently of acetate metabolism, is also required for maximum lifespan extension in the lipA and lpdA mutants, indicating that these mutations promote entry into a mode normally associated with a low-oxygen environment. Because analogous changes from respiration to fermentation have been observed in long-lived Saccharomyces cerevisiae and Caenorhabditis elegans strains, such metabolic alterations may represent an evolutionarily conserved strategy to extend lifespan.
 ...
PMID:Genome-wide screen identifies Escherichia coli TCA-cycle-related mutants with extended chronological lifespan dependent on acetate metabolism and the hypoxia-inducible transcription factor ArcA. 2070 65