Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound   Target Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound

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Query: EC:6.2.1.13 (acetyl-CoA synthetase)
451 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Acetaldehyde is one of the intermediate products of ethanolic fermentation, which can be reduced to ethanol by alcohol dehydrogenase (ADH). Alternatively, acetaldehyde can be oxidized to acetate by aldehyde dehydrogenase (ALDH) and subsequently converted to acetyl-CoA by acetyl-CoA synthetase (ACS). To study the expression of ALDHs in plants we isolated and characterized a cDNA coding for a putative mitochondrial ALDH (TobAldh2A) in Nicotiana tabacum. TobALDH2A shows 54-60% identity at the amino acid level with other ALDHs and shows 76% identity with maize Rf2, a gene involved in restoration of male fertility in cms-T maize. TobAldh2A transcripts and protein were present at high levels in the male and female reproductive tissues. Expression in vegetative tissues was much lower and no induction by anaerobic incubation was observed. This suggests that TobALDH expression is not part of the anaerobic response, but may have another function. The use of specific inhibitors of ALDH and the pyruvate dehydrogenase (PDH) complex indicates that ALDH activity is important for pollen tube growth, and thus may have a function in biosynthesis or energy production.
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PMID:Aldehyde dehydrogenase in tobacco pollen. 934 59

The KlPDA1 gene, encoding the E1alpha subunit of the mitochondrial pyruvate-dehydrogenase (PDH) complex was isolated from a Kluyveromyces lactis genomic library by screening with a 1.1 kb internal fragment of the Saccharomyces cerevisiae PDA1 gene. The predicted amino acid sequence encoded by KlPDA1 showed 87% similarity and 79% identity to its S. cerevisiae counterpart. Disruption of KIPDA1 resulted in complete absence of PDH activity in cell extracts. The maximum specific growth rate on glucose of null mutants was 3.5-fold lower than that of the wild-type, whereas growth on ethanol was unaffected. Wild-type K. lactis CBS 2359 exhibits a Crabtree-negative phenotype, i.e. no ethanol was produced in aerobic batch cultures grown on glucose. In contrast, substantial amounts of ethanol and acetaldehyde were produced in aerobic cultures of an isogenic Klpda1 null mutant. A wild-type specific growth rate was restored after introduction of an intact KlPDA1 gene but not, as previously found for S. cerevisiae pda1 mutants, by cultivation in the presence of leucine. The occurrence of aerobic fermentation and slow growth of the Klpda1 null mutant indicate that, although present, the enzymes of the PDH bypass (pyruvate decarboxylase, acetaldehyde dehydrogenase and acetyl-CoA synthetase) could not efficiently replace the PDH complex during batch cultivation on glucose. Only at relatively low growth rates (D = 0.10 h(-1)) in aerobic, glucose-limited chemostat cultures, could the PDH bypass completely replace the PDH complex, thus allowing fully respiratory growth. This resulted in a lower biomass yield [g biomass (g glucose)-1] than in the wild-type due to a higher consumption of ATP in the PDH bypass compared to the formation of acetyl-CoA via the PDH complex.
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PMID:Inactivation of the Kluyveromyces lactis KlPDA1 gene leads to loss of pyruvate dehydrogenase activity, impairs growth on glucose and triggers aerobic alcoholic fermentation. 988 36

Regulation of currently identified genes involved in pyruvate metabolism of Kluyveromyces lactis strain CBS 2359 was studied in glucose-limited, ethanol-limited and acetate-limited chemostat cultures and during a glucose pulse added to a glucose-limited steady-state culture. Enzyme activity levels of the pyruvate dehydrogenase complex, pyruvate decarboxylase, alcohol dehydrogenase, acetyl-CoA synthetase and glucose-6-phosphate dehydrogenase were determined in all steady-state cultures. In addition, the mRNA levels of KlADH1-4, KlACS1, KlACS2, KlPDA1, KlPDC1 and RAG1 were monitored under steady-state conditions and during glucose pulses. In K. lactis, as in Saccharomyces cerevisiae, enzymes involved in glucose utilization (glucose-6-phosphate dehydrogenase, pyruvate dehydrogenase, pyruvate decarboxylase) showed the highest expression levels on glucose, whereas enzymes required for ethanol or acetate consumption (alcohol dehydrogenase, acetyl-CoA synthetase) showed the highest enzyme activities on ethanol. In cases where mRNA levels were determined, these corresponded well with the corresponding enzyme activities, suggesting that regulation is mostly achieved at the transcriptional level. Surprisingly, the activity of the K. lactis pyruvate dehydrogenase complex appeared to be regulated at the level of KlPDA1 transcription. The conclusions from the steady-state cultures were corroborated by glucose pulse experiments. Overall, expression of the enzymes of pyruvate metabolism in the Crabtree-negative yeast K. lactis appeared to be regulated in the same way as in Crabtree-positive S. cerevisiae, with one notable exception: the PDA1 gene encoding the E1alpha subunit of the pyruvate dehydrogenase complex is expressed constitutively in S. cerevisiae.
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PMID:Regulation of pyruvate metabolism in chemostat cultures of Kluyveromyces lactis CBS 2359. 1080 23

Acetyl-coenzyme A (acetyl-CoA) formed within the plastid is the precursor for the biosynthesis of fatty acids and, through them, a range of important biomolecules. The source of acetyl-CoA in the plastid is not known, but two enzymes are thought to be involved: acetyl-CoA synthetase and plastidic pyruvate dehydrogenase. To determine the importance of these two enzymes in synthesizing acetyl-CoA during lipid accumulation in developing Arabidopsis seeds, we isolated cDNA clones for acetyl-CoA synthetase and for the ptE1alpha- and ptE1beta-subunits of plastidic pyruvate dehydrogenase. To our knowledge, this is the first reported acetyl-CoA synthetase sequence from a plant source. The Arabidopsis acetyl-CoA synthetase preprotein has a calculated mass of 76,678 D, an apparent plastid targeting sequence, and the mature protein is a monomer of 70 to 72 kD. During silique development, the spatial and temporal patterns of the ptE1beta mRNA level are very similar to those of the mRNAs for the plastidic heteromeric acetyl-CoA carboxylase subunits. The pattern of ptE1beta mRNA accumulation strongly correlates with the formation of lipid within the developing embryo. In contrast, the level of mRNA for acetyl-CoA synthetase does not correlate in time and space with lipid accumulation. The highest level of accumulation of the mRNA for acetyl-CoA synthetase during silique development is within the funiculus. These mRNA data suggest a predominant role for plastidic pyruvate dehydrogenase in acetyl-CoA formation during lipid synthesis in seeds.
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PMID:The role of pyruvate dehydrogenase and acetyl-coenzyme A synthetase in fatty acid synthesis in developing Arabidopsis seeds. 1085 80

We have characterized the expression of potential acetyl-CoA-generating genes (acetyl-CoA synthetase, pyruvate decarboxylase, acetaldehyde dehydrogenase, plastidic pyruvate dehydrogenase complex and ATP-citrate lyase), and compared these with the expression of acetyl-CoA-metabolizing genes (heteromeric and homomeric acetyl-CoA carboxylase). These comparisons have led to the development of testable hypotheses as to how distinct pools of acetyl-CoA are generated and metabolized. These hypotheses are being tested by combined biochemical, genetic and molecular biological experiments, which is providing insights into how acetyl-CoA metabolism is regulated.
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PMID:Molecular biology of acetyl-CoA metabolism. 1117 Nov 36

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.
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PMID:Pyruvate oxidase contributes to the aerobic growth efficiency of Escherichia coli. 1139 Jun 79

Rapid pollen tube growth requires a high rate of sugar metabolism to meet energetic and biosynthetic demands. Previous work on pollen sugar metabolism showed that tobacco pollen carry out efficient ethanolic fermentation concomitantly with a high rate of respiration (Bucher et al., 1995). Here we show that the products of fermentation, acetaldehyde and ethanol, are further metabolised in a pathway that bypasses mitochondrial PDH. The enzymes involved in this pathway are pyruvate decarboxylase, aldehyde dehydrogenase and acetyl-CoA synthetase. Radiolabelling experiments show that during tobacco pollen tube growth label of 14C-ethanol is incorporated into CO2 as well as into lipids and other higher molecular weight compounds. A role for the glyoxylate cycle appears unlikely since activity of malate synthase, a key enzyme of the glyoxylate cycle, could not be detected.
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PMID:The ethanolic fermentation pathway supports respiration and lipid biosynthesis in tobacco pollen. 1200 Jun 80

Some yeasts, such as Saccharomyces cerevisiae, produce ethanol at fully aerobic conditions, whereas other yeasts, such as Kluyveromyces lactis, do not. In this study we investigated the occurrence of aerobic alcoholic fermentation in the petite-negative yeast Saccharomyces kluyveri that is only distantly related to S. cerevisiae. In aerobic glucose-limited continuous cultures of S. kluyveri, two growth regimens were observed: at dilution rates below 0.5 h(-1) the metabolism was purely respiratory, and at dilution rates above 0.5 h(-1) the metabolism was respiro-fermentative. The dilution rate at which the switch in metabolism occurred, i.e. the critical dilution rate, was 66% higher than the typical critical dilution rate of S. cerevisiae. The maximum specific oxygen consumption rate around the critical dilution rate was found to 13.6 mmol (g dry weight)(-1) h(-1) and the capacity of the pyruvate dehydrogenase-bypass pathway was estimated to be high from in vitro enzyme activities; especially the specific activity of acetyl-CoA synthetase was much higher than in S. cerevisiae at all tested conditions. Addition of glucose to respiring cells of S. kluyveri led to ethanol formation after a delay of 20-50 min (depending on culture conditions prior to the pulse), which is in contrast to S. cerevisiae that ferments immediately after glucose addition.
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PMID:Steady-state and transient-state analyses of aerobic fermentation in Saccharomyces kluyveri. 1270 11

The aim of this work was to understand the steps controlling the process of biotransformation of trimethylamonium compounds into L(-)-carnitine by Escherichia coli and the link between the central carbon or primary and the secondary metabolism expressed. Thus, the enzyme activities involved in the biotransformation process of crotonobetaine into L(-)-carnitine (crotonobetaine hydration reaction and crotonobetaine reduction reaction), in the synthesis of acetyl-CoA (pyruvate dehydrogenase, acetyl-CoA synthetase, and ATP:acetate phosphotransferase) and in the distribution of metabolites for the tricarboxylic acid (isocitrate dehydrogenase) and glyoxylate (isocitrate lyase) cycles, were followed in batch with both growing and resting cells and during continuous cell growth in stirred-tank and high-cell-density membrane reactors. In addition, the levels of carnitine, crotonobetaine, gamma-butyrobetaine, ATP, NADH/NAD(+), and acetyl-CoA/CoA ratios were measured to determine how metabolic fluxes were distributed in the catabolic system. The results provide the first experimental evidence demonstrating the important role of the glyoxylate shunt during biotransformation of resting cells and the need for high levels of ATP to maintain metabolite transport and biotransformation (2.1 to 16.0 mmol L cellular/mmol ATP L reactor h). Moreover, the results obtained for the pool of acetyl-CoA/CoA indicate that it also correlated with the biotransformation process. The main metabolic pathway operating during cell growth in the high cell-density membrane reactor was that related to isocitrate dehydrogenase (during start-up) and isocitrate lyase (during steady-state operation), together with phosphotransacetylase and acetyl-CoA synthetase. More importantly, the link between central carbon and L(-)-carnitine metabolism at the level of the ATP pool was also confirmed.
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PMID:Link between primary and secondary metabolism in the biotransformation of trimethylammonium compounds by escherichia coli. 1459 81

Despite the importance of some Zygosaccharomyces species as agents causing spoilage of food, the carbon and energy metabolism of most of them is yet largely unknown. This is the case with Zygosaccharomyces bailii. In this study the occurrence of the Crabtree effect in the petite-negative yeast Z. bailii ATCC 36947 was investigated. In this yeast the aerobic ethanol production is strictly dependent on the carbon source utilised. In glucose-limited continuous cultures a very low level of ethanol was produced. In fructose-limited continuous cultures ethanol was produced at a higher level and its production increased with the dilution rate. As a consequence, on fructose the onset of respiro-fermentative metabolism caused a reduction in biomass yield. An immediate aerobic alcoholic fermentation in Z. bailii was observed during the transition from sugar limitation to sugar excess, both on glucose and on fructose. The analysis of some key enzymes of the fermentative metabolism showed a high level of acetyl-CoA synthetase in Z. bailii growing on fructose. At high dilution rates, the activities of glucose- and fructose-phosphorylating enzymes, as well as of pyruvate decarboxylase and alcohol dehydrogenase, were higher in cells during growth on fructose than on glucose.
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PMID:Aerobic sugar metabolism in the spoilage yeast Zygosaccharomyces bailii. 1465 32


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