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Query: EC:2.3.3.1 (citrate synthase)
 4,488 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Closed aorta working hearts perfused with 1 mM pyruvate were subjected to a 4-fold increase in work load by raising the left atrial filling pressure. Citric acid cycle flux, pyruvate uptake, and oxygen consumption rose 3-fold when cardiac output was increased. In the first 40 sec after the transition tissue glutamate and citrate fell by 22 and 45%, respectively, and there were reciprocal decreases in malate and aspartate. The ratio of creatine phosphate/creatine declined by 50% within 30 sec, with a corresponding increase in inorganic phosphate, but the fall in the ATP/ADP ratio was only 10%. During the first 10 sec the surface fluorescence from cardiac pyridine nucleotides fell by 30% and this change was synchronous with a sharp decline in the calculated adenine nucleotide phosphate potential. This suggests that heart mitochondrial respiration is controlled by the cytosolic phosphate potential, and that a state 4 to state 3 transition occurs when cardiac output is increased. Apparent disequilbrium of creatine phosphokinase can be explained by the compartmentation of most of the cardiac ADP within the mitochondria. Citric acid cycle flux was coordinated by activational interactions at citrate synthase, isocitrate dehydrogenase, and alpha-ketoglutarate dehydrogenase, but a transient imbalance between the individual cycle steps leads to a sharp peak of lactate production shortly after the work transition.
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PMID:Regulation of myocardial energy metabolism. 17 15

Electron paramagnetic resonance studies have indicated that nitrosodisulfonate binds to pig heart citrate synthase. Titration of the enzyme with nitrosodisulfonate revealed several binding sites for the probe per subunit with one site (KD approximately 0.1 mM) having a greater affinity than the others. The substrate, oxaloacetate, competed very effectively for one of the nitrosodisulfonate binding sites (KD less than 10(-2) mM) at the same time eliminating the weaker probe binding sites. Citrate and (R)- and (S)-malates also displaced the probe. Failure to resolve low- and high-field shoulder in the high gain--high modulation electron paramagnetic resonance spectra of the enzyme--nitrosodisulfonate system indicated that the bound probe was "weakly immobilized". However, the electron paramagnetic resonance spectrum of the bound probe changed to one typical of a "strongly immobilized" nitroxide upon the addition of a saturating concentration of the substrate acetyl coenzyme A (acetyl-CoA) to the enzyme--nitrosodisulfonate system, indicating the formation of a ternary acetyl-CoA-enzyme-probe complex. Titration of the acetyl-CoA saturated enzyme with the probe indicated one binding site per subunit (KD = 0.37 mM). Thus, nitrosodisulfonate may be considered as a paramagnetic analogue of oxaloacetate in its interaction with citrate synthase. These results are compared with our previous studies with this enzyme, employing a spin-labeled acyl coenzyme A (acyl-CoA) derivative [Weidman, S. W., Drysdale, G. R., & Mildvan, A. S. (1973) Biochemistry 12, 1874--1883].
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PMID:Interaction of a paramagnetic analogue of oxaloacetate with citrate synthase. 22 20

Levels of several intermediary metabolites were measured in cells grown in acetate medium in order to test the hypothesis that the glyoxylate cycle is repressed by phosphoenolpyruvate (PEP). Wild-type cells had less PEP than either isocitrate dehydrogenase - deficient cells (which had greater isocitrate lyase activity than the wild type) or isocitrate dehydrogenase - deficient, citrate synthase-deficient cells (which are poorly inducible). Thus induction of the glyoxylate cycle is more complicated than a simple function of PEP concentration. No correlation between enzyme activity and the level of oxaloacetate, pyruvate, or citrate was found either. Citrate was synthesized in citrate synthase-deficient mutants, possibly via citrate lyase.
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PMID:Acetate metabolism in Escherichia coli. 34 78

Enterobacter aerogenes was grown in continous culture with ammonia as the growth-limiting substrate, and changes in citrate lyase and citrate synthase activities were monitored after growth shifts from anaerobic growth on citrate to aerobic growth on citrate, aerobic growth on glucose, anaerobic growth on glucose, and anaerobic growth on glucose plus nitrate. Citrate lyase was inactivated during aerobic growth on glucose and during anaerobic growth with glucose plus nitrate. Inactivation did not occur during anaerobic growth on glucose, and as a result of the simultaneous presence of citrate lyase and citrate synthase, growth difficulties were observed. Citrate lyase inactivation consisted of deacetylation of the enzyme. The corresponding deacetylase could not be demonstrated in cell extracts, and it is concluded that, as in a number of other inactivations, electron transport to oxygen or nitrate was required for inactivation.
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PMID:Energy-dependent inactivation of citrate lyase in Enterobacter aerogenes. 92 71

The activity of key enzymes of the citrate and glyoxylate cycles was compared in yeast cells during intensive synthesis of citric acids and in its absence in the course of growth of Candida lipolytica on glucose ("glucose" yeast cells) and on hexadecane ("hexadecane" yeast cells). Citrate and isocitrate were found to be formed by the yeast in the tricarboxylic acid cycle. The ability of the yeast for "overproduction" of citrate and isocitrate during its growth on glucose and hexadecane depends on the high activity of the key enzyme of cycle, citrate synthase, as compared with the activity of other enzymes of the tricarboxylic acid cycle. Citrate predominated among excreted acids during growth on glucose in conditions of nitrogen deficiency while isocitrate prevailed during growth on hexadecane. The predominating synthesis of citrate in the first case seems to be related to a lower activity of aconitase in the "glucose" cells as compared with the "hexadecane" cells.
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PMID:[Enzyme activity of citrate, glyoxylate and pentosephosphate cycles during synthesis of citric acids by Candida lipolytica]. 100 46

The activity of "satellite" enzymes related to gluconeogenesis has been measured in the oocytes and embryos at the early stages of loach (Misgurnus fossilis L.) embryogenesis. The activity of pyruvate dehydrogenase increase during oocyte maturation by 30%, remains constant at the cleavage and blastula stages and decreased on the onset of gastrulation. In the both oocytes and embryos pyruvate dehydrogenase has been found only in the active form. The activity of citrate synthase, malate dehydrogenase and pyruvate carboxylase remained constant during oocyte maturation and et all early stage of embrional development. Citrate lyase and "malic"-enzyme were not found, Oocyte maturation is followed by a considerable increase in the malate and oxalacetate content, the level of pyruvate and acetyl-CoA being found invariable.
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PMID:[Characteristics of the activity of "satellite" enzymes of gluconeogenesis in the oocytes and embryos of loach]. 103 Jun 40

Citrate synthases from animal tissues were found to bind to Sepharose-"ATP." A pure preparation of citrate synthase was obtained from a crude fraction of rat heart by the specific elution of the enzyme from the Sepharose-"ATP" with the dead end complex-forming substrates, oxalacetate and CoA. The proposed mechanisms of citrate synthase, obtained from steady state kinetics, were examined in light of the elution pattern of the enzyme obtained using combinations of substrates and substrate analogs.
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PMID:Purification of and mechanism studies on citrate synthase. Use of biospecific adsorption-elution techniques. 125 79

Cells of Clostridium sporosphaeroides which were grown on citrate contained citrate lyase and citrate lyase acetylating enzyme, but no detectable citrate synthase and citrate lyase deacetylase activities. Citrate lyase from C. sporosphaeroides was purified to homogeneity as judged by polyacrylamide gel electrophoresis and high performance liquid chromatography. In contrast to the enzyme from Clostridium sphenoides, the addition of L-glutamate was not necessary for activity and stabilization of the enzyme. The purified enzyme had a specific activity of 34 U/mg protein and was comparable to other citrate lyases with respect to its molecular weight and subunit composition. Electron microscopic investigations showed that similar to the lyase from C. sphenoides and in contrast to all other citrate lyases examined so far, the majority of the enzyme molecules was present in "star" form.
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PMID:Characterization of citrate lyase from Clostridium sporosphaeroides. 399 85

Citrate specimens derived from chiral acetates were converted to the CoA derivatives. These were reconverted with citrate synthase to citrates under conditions of either predominating hydrolytic burst or predominating steady-state period. The stereochemical purity of substrates and products was determined. Reversal of the synthase condensation step occurs under both conditions but is markedly increased during the steady-state period. The results indicate that citryl-CoA-derived acetyl-CoA and oxaloacetate create the steady-state conditions. The hydrolase state and the ligase/lyase state of the synthase predominate under burst and steady-state conditions, respectively. This result indicates a conversion of the hydrolase state into the ligase/lyase state during the transition.
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PMID:Hysteretic behaviour of citrate synthase. Isotopically chiral citryl-CoA reveals increased number of reversals of the synthase condensation step under steady-state conditions. 401 81

1. The fixation of CO(2) by pyruvate carboxylase in isolated rat brain mitochondria was investigated. 2. In the presence of pyruvate, ATP, inorganic phosphate and magnesium, rat brain mitochondria fixed H(14)CO(3) (-) into tricarboxylic acid-cycle intermediates at a rate of about 250nmol/30min per mg of protein. 3. Citrate and malate were the main radioactive products with citrate containing most of the radioactivity fixed. The observed rates of H(14)CO(3) (-) fixation and citrate formation correlated with the measured activities of pyruvate carboxylase and citrate synthase in the mitochondria. 4. The carboxylation of pyruvate by the mitochondria had an apparent K(m) for pyruvate of about 0.5mm. 5. Pyruvate carboxylation was inhibited by ADP and dinitrophenol. 6. Malate, succinate, fumarate and oxaloacetate inhibited the carboxylation of pyruvate whereas glutamate stimulated it. 7. The results suggest that the metabolism of pyruvate via pyruvate carboxylase in brain mitochondria is regulated, in part, by the intramitochondrial concentrations of pyruvate, oxaloacetate and the ATP:ADP ratio.
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PMID:Regulation of pyruvate metabolism via pyruvate carboxylase in rat brain mitochondria. 472 35


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