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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)

Acetyl-coenzyme A synthetase (EC 6.2.1.1) activity of Saccharomyces cerevisiae was determined by a radioactive assay procedure. The activity in vitro was inhibited significantly by NADPH, NADH, or AMP and to a lesser extent by NADP, NAD, or ADP. Glutamic acid and alpha-ketoglutaric acid were not inhibitory. The enzyme level was repressed when the cells were grown in a complex nutrient medium as opposed to the minimal medium. However, a glutamic acid auxotroph glul, when grown in excess glutamic acid, demonstrated a fivefold increase of acetyl-CoA synthetase.
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PMID:Regulation of acetyl-CoA synthetase of Saccharomyces cerevisiae. 0 41

In experimental rat liver perfusion we observed net production of free acetate accompanied by accelerated ketogenesis with long-chain fatty acids. Mitochondrial acetyl-CoA hydrolase, responsible for the production of free acetate, was found to be inhibited by the free form of CoA in a competitive manner and activated by reduced nicotinamide adenine dinucleotide (NADH). The conditions under which the ketogenesis was accelerated favored activation of the hydrolase by dropping free CoA and elevating NADH levels. Free acetate was barely metabolized in the liver because of low affinity, high K(m), of acetyl coenzyme A (acetyl-CoA) synthetase for acetate. Therefore, infused ethanol was oxidized only to acetate, which was entirely excreted into the perfusate. The acetyl-CoA synthetase in the heart mitochondria was much lower in K(m) than it was in the liver, thus the heart mitochondria was capable of oxidizing free acetate as fast as other respiratory substrates, such as succinate. These results indicate that rat liver produces free acetate as a byproduct of ketogenesis and may supply free acetate, as in the case of ketone bodies, to extrahepatic tissues as fuel.
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PMID:Production of acetate in the liver and its utilization in peripheral tissues. 1142 Jan 76

Ethanol metabolism in Acinetobacter sp. is limited by the rate of acetate assimilation in a reaction catalyzed by acetyl-CoA synthetase (EC 6.2.1.1). Effects of ions (sodium, potassium, and magnesium), byproducts of ethanol and acetaldehyde oxidation (NADH and NADPH), and pantothenic acid on this enzyme have been studied (sodium, NADH, and NADPH inhibit acetyl-CoA synthetase; pantothenic acid, potassium, and magnesium act as the enzyme activators). Conditions of culturing were developed, under which ethanol, acetaldehyde, and acetate in Acinetobacter cells were oxidized at the same rates, producing a threefold increase in the activity of acetyl-CoA synthetase in the cell-free extract. The results of studies of acetyl-CoA synthetase regulation in a mutant strain of Acinetobacter sp., which is incapable of forming exopolysaccharides, provide a basis for refining the technology of ethapolan production, involving the use of C2 substrates.
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PMID:[Regulation of acetate metabolism in a strain of Acinetobacter sp., growing on ethanol]. 1272 51

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

The aim was to understand how interaction of the central carbon and the secondary carnitine metabolisms is affected under salt stress and its effect on the production of L-carnitine by Escherichia coli. The biotransformation of crotonobetaine into L-carnitine by resting cells of E. coli O44 K74 was improved by salt stress, a yield of nearly twofold that for the control being obtained with 0.5 M NaCl. Crotonobetaine and the L-carnitine formed acted as an osmoprotectant during cell growth and biotransformation in the presence of NaCl. The enzyme activities involved in the biotransformation process (crotonobetaine hydration reaction and crotonobetaine reduction reaction), in the synthesis of acetyl-CoA/acetate (pyruvate dehydrogenase, acetyl-CoA synthetase [ACS] and ATP/acetate phosphotransferase) and in the distribution of metabolites for the tricarboxylic acid cycle (isocitrate dehydrogenase [ICDH]) and glyoxylate shunt (isocitrate lyase [ICL]) were followed in batch with resting cells both in the presence and absence of NaCl and in perturbation experiments performed on growing cells in a high density cell recycle membrane reactor. Further, the levels of carnitine, crotonobetaine, gamma-butyrobetaine and ATP and the NADH/NAD(+) ratio were measured in order to know how the metabolic state was modified and coenzyme pools redistributed as a result of NaCl's effect on the energy content of the cell. The results provided the first experimental evidence of the important role played by salt stress during resting and growing cell biotransformation (0.5 M NaCl increased the L-carnitine production in nearly 85%), and the need for high levels of ATP to maintain metabolite transport and biotransformation. Moreover, the main metabolic pathways and carbon flow operating during cell biotransformation was that controlled by the ICDH/ICL ratio, which decreased from 8.0 to 2.5, and the phosphotransferase/ACS ratio, which increased from 2.1 to 5.2, after a NaCl pulse fivefold the steady-state level. Resting E. coli cells were seen to be made up of heterogeneous populations consisting of several types of subpopulation (intact, depolarized, and permeabilized cells) differing in viability and metabolic activity as biotransformation run-time and the NaCl concentration increased. The results are discussed in relation with the general stress response of E. coli, which alters the NADH/NAD(+) ratio, ATP content, and central carbon enzyme activities.
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PMID:Salt stress effects on the central and carnitine metabolisms of Escherichia coli. 1689 34

The aim of this work was to understand the steps controlling the biotransformation of trimethylammonium compounds into L(-)-carnitine by Escherichia coli. The high-cell density reactor steady-state levels of carbon source (glycerol), biotransformation substrate (crotonobetaine), acetate (anaerobiosis product) and fumarate (as an electron acceptor) were pulsed by increasing them fivefold. Following the pulse, the evolution of the enzyme activities involved in the biotransformation process of crotonobetaine into L(-)-carnitine (crotonobetaine hydration), in the synthesis of acetyl-CoA (ACS: acetyl-CoA synthetase and PTA: ATP: acetate phosphotransferase) and in the distribution of metabolites for the tricarboxylic acid (ICDH: isocitrate dehydrogenase) and glyoxylate (ICL: isocitrate lyase) cycles was monitored. In addition, the levels of carnitine, the cell ATP content and the NADH/NAD(+) ratio were measured in order to assess the importance and participation of these energetic coenzymes in the catabolic system. The results provided an experimental demonstration of the important role of the glyoxylate shunt during biotransformation and the need for high levels of ATP to maintain metabolite transport and biotransformation. Moreover, the results obtained for the NADH/NAD(+) pool indicated that it is correlated with the biotransformation process at the NAD(+) regeneration and ATP production level in anaerobiosis. More importantly, a linear correlation between the NADH/NAD(+) ratio and the levels of the ICDH and ICL (carbon and electron flows) and the PTA and ACS (acetate and ATP production and acetyl-CoA synthesis) activity levels was assessed. The main metabolic pathway operating during cell metabolic perturbation with a pulse of glycerol and acetate in the high-cell density membrane reactor was that related to ICDH and ICL, both regulating the carbon metabolism, together with PTA and ACS enzymes (regulating ATP production).
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PMID:Role of energetic coenzyme pools in the production of L-carnitine by Escherichia coli. 1690 59

The function of the N-terminal domain ( approximately 350 residues) of the Pta (phosphotransacetylase) enzyme of Salmonella enterica is unclear. Results from in vivo genetic and in vitro studies suggest that the N-terminal domain of Pta is a sensor for NADH and pyruvate. We isolated 10 single-amino acid variants of Pta that, unlike the wild-type protein, supported growth of a strain of S. enterica devoid of Acs (acetyl-CoA synthetase; AMP-forming) activity on 10 mm acetate. All mutations were mapped within the N-terminal domain of the protein. Kinetic analyses of the wild type and three variant Pta proteins showed that two of the variant proteins were faster enzymes (k(cat) 2.5-3-fold > k(cat) Pta(WT). Results from sedimentation equilibrium experiments are consistent with Pta(WT) being a trimer. Pta variants formed more hexamer than the Pta(WT) protein. NADH inhibited Pta(WT) activity by inducing a conformational change detectable by limited trypsin proteolysis; NADH did not inhibit variant protein Pta(R252H). Pyruvate stimulated Pta(WT) activity, and its effect was potentiated in the variants, being most pronounced on Pta(R252H).
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PMID:In vivo and in vitro analyses of single-amino acid variants of the Salmonella enterica phosphotransacetylase enzyme provide insights into the function of its N-terminal domain. 1733 19

Escherichia coli phosphotransacetylase (Pta) catalyzes the reversible interconversion of acetyl-CoA and acetyl phosphate. Both compounds are critical in E. coli metabolism, and acetyl phosphate is also involved in the regulation of certain signal transduction pathways. Along with acetate kinase, Pta plays an important role in acetate production when E. coli grows on rich medium; alternatively, it is involved in acetate utilization at high acetate concentrations. E. coli Pta is composed of three different domains, but only the C-terminal one, called PTA_PTB, is specific for all Ptas. In the present work, the characterization of E. coli Pta and deletions from the N-terminal region were performed. E. coli Pta acetyl phosphate-forming and acetyl phosphate-consuming reactions display different maximum activities, and are differentially regulated by pyruvate and phosphoenolpyruvate. These compounds activate acetyl phosphate production, but inhibit acetyl-CoA production, thus playing a critical role in defining the rates of the two Pta reactions. The characterization of three truncated Ptas, which all display Pta activity, indicates that the substrate-binding site is located at the C-terminal PTA_PTB domain. However, the N-terminal P-loop NTPase domain is involved in expression of the maximal catalytic activity, stabilization of the hexameric native state, and Pta activity regulation by NADH, ATP, phosphoenolpyruvate, and pyruvate. The truncated protein Pta-F3 was able to complement the growth on acetate of an E. coli mutant defective in acetyl-CoA synthetase and Pta, indicating that, although not regulated by metabolites, the Pta C-terminal domain is active in vivo.
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PMID:Functional dissection of Escherichia coli phosphotransacetylase structural domains and analysis of key compounds involved in activity regulation. 2023 19

The modified electrode for electrocatalytic oxidation of NADH was developed using a pH-switchable redox interface. The operation of the modified electrode was controlled by logic operations performed by enzyme systems processing biochemical input signals. The electrocatalytic oxidation of NADH was activated upon appropriate combinations of the signals processed by the AND/OR logic operations performed by the enzymes. The modified interface was reset in a mute nonactive state by another enzyme reaction. The coupling between the enzyme logic systems and the bioelectrocatalytic interface was achieved by pH changes produced in situ by the enzyme reactions, resulting in different protonation states of the polymeric matrix associated with the electrode surface. The bioelectrocatalytic system integrated with biochemical computing systems opens the way to novel "smart" interfaces for multisignal biosensors and signal-controlled biofuel cells. In a long perspective, this approach will allow physiological control of implantable bioelectronic devices.
ACS Appl Mater Interfaces 2009 Jan
PMID:Bioelectrocatalytic system coupled with enzyme-based biocomputing ensembles performing boolean logic operations: approaching "smart" physiologically controlled biointerfaces. 2035 66

Redox-active molecular architectures are electrochemically derived on the electrode surface by Michael addition reaction of o-quinone with surface adsorbed nucleophiles. Electrogenerated o-quinone undergoes facile Michael addition reaction with nucleophile mercaptotriazole (MTz) and mercaptoimidazole (MIm) preassembled on Au electrode. The Michael addition reaction yields redox molecular architectures of 4-(3-mercapto-[1,2,4]triazol-1-yl)-benzene-1,2-diol (MTBD) and 4-(2-mercapto-imidazol-1-yl)-benzene-1,2-diol (MIBD). Solution pH controls the Michael addition reaction; the reaction of o-quinone with MTz nucleophile is more favorable in neutral pH whereas it is favorable in pH >or=9 with MIm. Michael addition of electrogenerated o-quinone with the nucleophile is quantitatively followed in real time using electrochemical quartz crystal microbalance (EQCM). The redox molecular architecture on the electrode surface is characterized by attenuated total reflection (ATR) spectral and electrochemical measurements. ATR spectral measurement confirms the Michael addition with the nucleophile. The redox molecular architecture displays reversible voltammetric response at 0.2 V corresponding to the redox reaction surface confined catechol moiety. The surface coverage of MTBD and MIBD on the electrode surface at pH 7.2 is estimated to be (5.4 +/- 0.2) x 10(-10) and (2.0 +/- 0.2) x 10(-10) mol/cm(2), respectively. Both redox molecular assemblies efficiently mediate the oxidation of reduced nicotinamide adenine dinucleotide (NADH) at a favorable potential. A large decrease in the overpotential associated with an enhancement in the voltammetric peak current with respect to the unmodified electrode is observed. Flow injection amperometric sensing of NADH is performed at the potential of 230 mV. These modified electrodes could detect NADH at micromolar level. Mixed molecular architecture of cysteamine (CYST) and MTz/MIm are developed for the interference free voltammetric sensing of NADH.
ACS Appl Mater Interfaces 2010 May
PMID:Electrochemically derived redox molecular architecture: a novel electrochemical interface for voltammetric sensing. 2042 26


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