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

1. The activities of citrate synthase and NAD+-linked and NADP+-linked isocitrate dehydrogenases were measured in nervous tissue from different animals in an attempt to provide more information about the citric acid cycle in this tissue. In higher animals the activities of citrate synthase are greater than the sum of activities of the isocitrate dehydrogenases, whereas they are similar in nervous tissues from the lower animals. This suggests that in higher animals the isocitrate dehydrogenase reaction is far-removed from equilibrium. If it is assumed that isocitrate dehydrogenase activities provide an indication of the maximum flux through the citric acid cycle, the maximum glycolytic capacity in nervous tissue is considerably greater than that of the cycle. This suggest that glycolysis can provide energy in excess of the aerobic capacity of the tissue. 2. The activities of glutamate dehydrogenase are high in most nervous tissues and the activities of aspartate aminotransferase are high in all nervous tissue investigated. However, the activities of alanine aminotransferase are low in all tissues except the ganglia of the waterbug and cockroach. In these insect tissues, anaerobic glycolysis may result in the formation of alanine rather than lactate.
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PMID:Activities of citrate synthase, NAD+-linked and NADP+-linked isocitrate dehydrogenases, glutamate dehydrogenase, aspartate aminotransferase and alanine aminotransferase in nervous tissues from vertebrates and invertebrates. 0 Oct 3

A 10 month old female infant was evaluated for severe lactic acidosis. Clinically she was well nourished and had a substantial amount of adipose tissue despite recurrent episodes of acidosis. Her psychomotor development was retarded, her movements were dystonic and generalized seizures punctuated her course. Metabolic abnormalities included elevated blood concentrations of lactate, pyruvate, beta-hydroxybutyrate, acetoacetate, alanine, proline and glycine, decreased blood concentrations of glutamine, aspartate, valine and citrate, and intermittent elevations of serum cholesterol. A trial on a high-fat diet worsened the clinical condition and intensified the ketoacidosis and hyperalaninemia. Analysis of hepatic tissue obtained by open biopsy revealed increased concentrations of lactate, alanine, acetyl-CoA and other short-chain acyl-CoA esters, and decreased concentrations of oxaloacetate, citrate, alpha-ketoglutarate, malate and aspartate. The blood and tissue metabolic perturbations reflected a deficiency of hepatic pyruvate carboxylase. The apparent Km of hepatic citrate synthase for oxaloacetate was 4.6 micrometer. Calculated tissue oxaloacetate concentrations were 0.50--0.84 micrometer suggesting that tricarboxylic acid cycle activity was severely limited by the decreased availability of this substrate. An iv glucose tolerance test resulted in the paradoxical synthesis of ketone bodies. This observation, coupled with the intermittent hypercholesterolemia and the increased tissue acetyl-CoA concentrations, suggests that pyruvate carboxylase is important in modulating the fractional distribution of intracellular acetyl-CoA between the tricarboxylic acid cycle, the beta-hydroxy-beta-methyl-glutaryl-CoA cycle (and the synthesis of cholesterol and ketone bodies), and fatty acid synthesis. Treatment in future cases might be directed toward increasing tissue concentrations of oxaloacetate.
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PMID:The clinical and biochemical implications of pyruvate carboxylase deficiency. 41 60

1. The contents of some intermediates of glycolysis, the citric acid cycle and adenine nucleotides have been measured in the freeze-clamped locust flight muscle at rest and after 10s and 3min flight. The contents of glucose 6-phosphate, pyruvate, alanine and especially fructose bisphosphate and triose phosphates increased markedly upon flight. The content of acetyl-CoA is decreased after 3min flight whereas that of acetylcarnitine is decreased markedly after 10s flight, but returns towards the resting value after 3min flight. The content of citrate is markedly decreased after both 10s and 3min flight, whereas that of isocitrate is changed very little after 10s and is increased by 50% after 3min. The content of oxaloacetate is very low in insect flight muscle and hence it was measured by a sensitive radiochemical assay. The content of oxaloacetate increased about 2-fold after 3min flight. A similar change was observed in the content of malate. The content of ATP decreased about 15%, whereas those of ADP and AMP increased about 2-fold after 3min flight. 2. Calculations based on O(2) uptake of the intact insect indicate that the rate of the citric acid cycle must be increased >100-fold during flight. Consequently, if citrate synthase catalyses a non-equilibrium reaction, the activity of the enzyme must increase >100-fold during flight. However, changes in the concentrations of possible regulators of citrate synthase, oxaloacetate, acetyl-CoA and citrate (which is an allosteric inhibitor), are not sufficient to account for this change in activity. It is concluded that there may be much larger changes in the free concentration of oxaloacetate than are indicated by the changes in the total content of this metabolite or that other unknown factors must play an additional role in the regulation of citrate synthase activity. 3. The increased content of oxaloacetate could be produced via pyruvate carboxylase, which may be stimulated during the early stages of flight by the increased concentration of pyruvate. 4. The decreases in the concentrations of citrate and alpha-oxoglutarate indicate that isocitrate dehydrogenase and oxoglutarate dehydrogenase may be stimulated by factors other than their pathway substrates during the early stages of flight. 5. Calculated mitochondrial and cytosolic NAD(+)/NADH ratios are both increased upon flight. The change in the mitochondrial ratio indicates the importance of the intramitochondrial ATP/ADP concentration ratio in the regulation of the rate of electron transfer in this muscle.
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PMID:Changes in the contents of adenine nucleotides and intermediates of glycolysis and the citric acid cycle in flight muscle of the locust upon flight and their relationship to the control of the cycle. 43 78

In isolated hepatocytes from normal fed rats, the subcellular distribution of malate, citrate, 2-oxoglutarate, glutamate, aspartate, oxaloacetate, acetyl-CoA and CoASH has been determined by a modified digitonin method. Incubation with various substrates (lactate, pyruvate, alanine, oleate, oleate plus lactate, ethanol and aspartate) markedly changed the total cellular amounts of metabolites, but their distribution between the cytosolic and mitochondrial compartments was kept fairly constant. In the presence of lactate, pyruvate or alanine, about 90% of cellular aspartate, malate and oxaloacetate, and 50% of citrate was located in the cytosol. The changes in acetyl-CoA in the cytosol were opposite to those in the mitochondrial space, the sum of both remaining nearly constant. The mitochondrial acetyl-CoA/CoASH ratio ranged from 0.3-0.9 and was positively correlated with the rate of ketone body formation. The mitochondrial/cytosolic (m/c) concentration gradients for malate, citrate, 2-oxoglutarate, glutamate, aspartate, oxaloacetate, acetyl-CoA and CoASH averaged from hepatocytes under different substrate conditions were determined to be 1.0, 8.8, 1.6, 2.2, 0.5, 0.7, 13 and 40, respectively. From the distribution of citrate, a pH difference of 0.3 across the inner mitochondrial membrane was calculated, yet lower values resulted from the m/c gradients of 2-oxoglutarate, glutamate and malate. The mass action ratios for citrate synthase and mitochondrial aspartate aminotransferase have been calculated from the metabolite concentrations measured in the mitochondrial pellet fraction. A comparison with the respective equilibrium constants indicates that in intact hepatocytes, neither enzyme maintains its reactants at equilibrium. On the assumption that mitochondrial malate dehydrogenase and 3-hydroxybutyrate dehydrogenase operate near equilibrium, the concentration of free oxaloacetate appears to be 0.3-2 micron, depending on the substrate used. Plotting the calculated free mitochondrial oxaloacetate concentration against the citrate concentration measured in the mitochondrial pellet yielded a hyperbolic saturation curve, from which an apparent Km of citrate synthase for oxaloacetate in the intact cells of 2 micron can be derived, which is comparable to the value determined with purified rat liver citrate synthase. The results are discussed with respect to the supply of substrates and effectors of anion carriers and of key enzymes of the tricarboxylic acid cycle and fatty acid biosynthesis.
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PMID:Distribution of metabolites between the cytosolic and mitochondrial compartments of hepatocytes isolated from fed rats. 68 Jun 39

Glutamate-auxotrophic mutants lacking phosphoenolpyruvate carboxylase(PC), citrate synthase (CS) or glutamate dehydrogenase (GD), an aspartate auxotroph lacking aspartate aminotransferase (TA), and a glutamate-aspartate double auxotroph lacking both aconitase (AH) and TA were obtained from Brevibacterium flavum No. 2247, a glutamate-producing bacterium. Prototrophic revertants further derived from the CS- and GD-lacking auxotrophs concomitantly recovered the enzyme activities that their parents had lost. These results indicate involvement of the tricarboxylic acid (TCA) cycle and GD in glutamate biosynthesis, that of PC in the biosynthesis of the TCA cycle intermediates and that of TA in aspartate biosynthesis. The CS-deficient mutants accumulated large amounts of acetate and small amounts of pyruvate, aspartate and alanine, while the GD-deficient strains accumulated large amounts of 2-oxo-glutarate and small amounts of citrate. Synthesis of PC was repressed by either glutamate or aspartate and those of CS and GD were repressed by glutamate, whereas those of pyruvate dehydrogenase (PD), AH, and isocitrate dehydrogenase were not affected significantly by glutamate; that of TA was also not affected by aspartate or by glutamate. The specific activities of PD and AH gave peaks during the cellular cultivation, related to the temporary accumulation of their substrates, pyruvate and citrate, respectively. These and previous results on the regulation of the enzymatic activities provide a definite regulatory mechanism for glutamate and aspartate syntheses.
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PMID:Enzymes of the glutamate and aspartate synthetic pathways in a glutamate-producing bacterium, Brevibacterium flavum. 72 99

The pathway of acetate assimilation in Methanosarcina barkeri was determined from analysis of the position of label in alanine, aspartate, and glutamate formed in cells grown in the presence of [14C]acetate and by measurement of enzyme activities in cell extracts. The specific radioactivity of glutamate from cells grown on [1-14C]- or [2-14C]acetate was approximately twice that of aspartate. The methyl and carboxyl carbons of acetate were incorporated into aspartate and glutamate to similar extents. Degradation studies revealed that acetate was not significantly incorporated into the C1 of alanine, C1 or C4 of aspartate, or C1 of glutamate. The C5 of glutamate, however, was partially derived from the carboxyl carbon of acetate. Cell extracts were found to contain the following enzyme activities, in nanomoles per minute per milligram of protein at 37 degrees C: F420-linked pyruvate synthase, 170; citrate synthase, 0.7; aconitase, 55; oxidized nicotinamide adenine dinucleotide phosphate-linked isocitrate dehydrogenase, 75; and oxidized nicotinamide adenine dinucleotide-linked malate dehydrogenase, 76. The results indicate that M. barkeri assimilates acetate into alanine and aspartate via pyruvate and oxaloacetate and into glutamate via citrate, isocitrate, and alpha-ketoglutarate. The data reveal differences in the metabolism of M. barkeri and Methanobacterium thermoautotrophicum and similarities in the assimilation of acetate between M. barkeri and other anaerobic bacteria, such as Clostridium kluyveri.
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PMID:Acetate assimilation pathway of Methanosarcina barkeri. 76 16

beta-Ketoacyl-acyl carrier protein (ACP) synthase III catalyzes the condensation of acetyl-CoA with malonyl-ACP in dissociated (Type II) fatty acid synthase systems. A synthase III mutant was used to localize the structural gene to the 24.5-min region of the Escherichia coli chromosome, and the defective synthase III allele was designated fabH1. The fabH gene was identified on a 1.3-kilobase NruI-HindIII chromosomal DNA fragment (plasmid pWO114) that complemented the enzymatic defect in fabH1 strains. The NruI-HindIII fragment was sequenced and contained a single open reading frame predicted to encode a 33,517-dalton protein with an isoelectric point of 4.85. The fabH sequence contained an Ala-Cys-Ala tripeptide characteristic of condensing enzyme active sites. A T7 expression system showed that the NruI-HindIII fragment directed the synthesis of a single 34,800-dalton protein. This protein was purified and the order of the amino-terminal 30 residues of the protein corresponded exactly to the amino acid structure predicted from the DNA sequence. The purified protein possessed both acetoacetyl-ACP synthase and acetyl-CoA:ACP transacylase activities, and cells harboring plasmid pWO114 overproduced the two activities, supporting the conclusion that a single protein carries out both reactions. Overproduction of synthase III resulted in a significant increase in shorter-chain fatty acids in the membrane phospholipids. These catalytic properties are consistent with the proposed role of synthase III in the initiation of fatty acid synthesis.
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PMID:Isolation and characterization of the beta-ketoacyl-acyl carrier protein synthase III gene (fabH) from Escherichia coli K-12. 155 88

1. The metabolism of glucose and glutamine was studied in the small intestine and the colon of rats after 4-5 weeks of hypothyroidism. 2. Hypothyroidism resulted in increases in the plasma concentrations of ketone bodies (P less than 0.05), cholesterol (P less than 0.001) and urea (P less than 0.001), but decreases in the plasma concentrations of free fatty acids (P less than 0.05) and triacylglycerol (P less than 0.001). These changes were associated with decreases in the plasma concentrations of total tri-iodothyronine, free tri-iodothyronine, total thyroxine and free thyroxine. 3. Hypothyroidism decreased both the DNA content (by 30.5%) and the protein content (by 23.6%) of intestinal mucosa, with the protein/DNA ratio remaining unchanged. The villi in the jejunum were shorter (P less than 0.05) and the crypt depth was decreased by about 26.5% in hypothyroid rats. 4. Portal-drained visceral blood flow showed no marked change in response to hypothyroidism, but was accompanied by decreased rates of extraction of glucose, lactate and glutamine and release of glutamate, alanine and ammonia. 5. Enterocytes and colonocytes isolated from hypothyroid rats showed decreased rates of utilization and metabolism of glucose and glutamine. 6. The maximal activities of hexokinase (EC 2.7.1.1), 6-phosphofructokinase (EC 2.7.1.11), pyruvate kinase (EC 2.7.1.40), citrate synthase (EC 4.1.3.28), oxoglutarate dehydrogenase (EC 1.2.4.2) and phosphate-dependent glutaminase (EC 3.5.1.2) were decreased in intestinal mucosal scrapings from hypothyroid rats. Similar decreases were obtained in colonic mucosal scrapings (except for citrate synthase and oxoglutarate dehydrogenase) from hypothyroid rats.(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:Effects of hypothyroidism on glucose and glutamine metabolism by the gut of the rat. 165 36

We describe a mutant of Escherichia coli citrate synthase, CS R319L, in which the arginine residue at position 319 of the sequence has been replaced by leucine. In this mutant, saturation by the substrate acetyl-CoA is changed from sigmoid (Hill parameter = 1.75 +/- 0.2) to hyperbolic (Hill parameter = 1.0 +/- 0.1) and dependence on the activator KCl is greatly reduced. Further mutations at this site and at position 343 (which model building predicts is close enough to allow a side-chain interaction with position 319) are also described. In the wild-type enzyme, the model suggests the possibility of a salt-bridge interaction between Arg-319 (located on the P helix in the small domain) and Glu-343 (in the Q helix in the same domain), but mutation of Glu-343 to Ala (CS E343A) produced a much smaller difference in the kinetic properties than the ARg-319 to Leu mutation did. Small changes in kinetic properties were also obtained with an Arg-319----Glu (CS R319E) mutation. In CS R319L, oxaloacetate, the first substrate to bind, induces an ultraviolet difference spectrum which is obtained with wild-type enzyme only in the presence of KCl. To account for these observations we postulate that wild-type E. coli citrate synthase exists in two conformational states, T and R, which are equilibrium; T state binds NADH, the allosteric inhibitor, while R state binds substrates and can be converted to another substrate-binding state, R', by KCl.(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:A mutant of Escherichia coli citrate synthase that affects the allosteric equilibrium. 167 60

The anaplerotic hypothesis for insulin release postulates that an increased generation of malonyl-CoA, acyl residues and diacylglycerol in nutrient-stimulated pancreatic islets may couple the catabolism of nutrient secretagogues to more distal events in the secretory sequence. In the light of this hypothesis, pyruvate carboxylase activity was measured in rat pancreatic islets using two distinct radioisotopic procedures. The first procedure is based on the conversion of oxalacetate generated from pyruvate to 14C-labelled citrate in the presence of [1-14C]acetyl-CoA and citrate synthase. The second technique involves the conversion of 14C-labelled oxalacetate generated from [1-14C]pyruvate to radioactive aspartate in the presence of L-glutamate and glutamate-oxalacetate transaminase. Pyruvate carboxylase activity amounted to 10 pmol/min per islet, was restricted to mitochondria, displayed a Km for pyruvate close to 0.4 mM, and demonstrated dependency towards ATP (apparent Ka close to 0.1 mM), Mg2+ and acetyl-CoA. It is proposed that pyruvate carboxylase activity accounts for the generation of 14C-labelled amino acids other than alanine in islets exposed to D-[3,4-14C]glucose and participates to the pyruvate/citrate shuttle for the transport of acetyl-CoA out of the mitochondria in nutrient-stimulated islets.
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PMID:Hexose metabolism in pancreatic islets: pyruvate carboxylase activity. 176 3


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