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

1. The activities of citrate synthase, NAD+-linked and NADP+-linked isocitrate dehydrogenase were measured in muscles from a large number of animals, in order to provide some indication of the importance of the citric acid cycle in these muscles. According to the differences in enzyme activities, the muscles can be divided into three classes. First, in a number of both vertebrate and invertebrate muscles, the activities of all three enzymes are very low. It is suggested that either the muscles use energy at a very low rate or they rely largely on anaerobic glycolysis for higher rates of energy formation. Second, most insect flight muscles contain high activities of citrate synthase and NAD+-linked isocitrate dehydrogenase, but the activities of the NADP+-linked enzyme are very low. The high activities indicate the dependence of insect flight on energy generated via the citric acid cycle. The flight muscles of the beetles investigated contain high activities of both isocitrate dehydrogenases. Third, other muscles of both vertebrates and invertebrates contain high activities of citrate synthase and NADP+-liniked isocitrate dehydrogenase. Many, if not all, of these muscles are capable of sustained periods of mechanical activity (e.g. heart muscle, pectoral muscles of some birds). Consequently, to support this activity fuel must be supplied continually to the muscle via the circulatory system which, in most animals, also transports oxygen so that energy can be generated by complete oxidation of the fuel. It is suggested that the low activities of NAD+-linked isocitrate dehydrogenase in these muscles may be involved in oxidation of isocitrate in the cycle when the muscles are at rest. 2. A comparison of the maximal activities of the enzymes with the maximal flux through the cycle suggests that, in insect flight muscle, NAD+-linked isocitrate dehydrogenase catalyses a non-equilibrium reaction and citrate synthease catalyses a near-equilibrium reaction. In other muscles, the enzyme-activity data suggest that both citrate synthase and the isocitrate dehydrogenase reactions are near-equilibrium.
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PMID:Activities of citrate synthase and NAD+-linked and NADP+-linked isocitrate dehydrogenase in muscle from vertebrates and invertebrates. 0 36

A protease from Tetrahymena pyriformis inactivated eight of nine commercially available enzymes tested, including lactate deyhdrogenase, isocitrate dehydrogenase (TPN-specific), glucose-6 phosphate dehydrogenase, D-amino acid oxidase, fumarase, pyruvate kinase, hexokinase, and citrate synthase. Urate oxidase was not inactivated. Inactivation occurred at neutral pH, was prevented by inhibitors of the protease, and followed first order kinetics. In those cases tested, inactivation was enhanced by mercaptoethanol. Most of the enzyme-inactivating activity was due to a protease of molecular weight 25,000 that eluted from DEAE-Sephadex at 0.3 M KCl. A second protease of this molecular weight, which was not retained by the gel, inactivated only isocitrate dehydrogenase and D-amino acid oxidase. These two proteases could also be distinguished by temperature and inhibitor sensitivity. Two other protease peaks obtained by DEAE-Sephadex chromatography had little or no no enzyme inactivating activity, while another attacked only D-amino acid oxidase. At least six of the enzymes could be protected from proteolytic inactivation by various ligands. Isocitrates dehydrogenase was protected by isocitrate, TPN, or TPNH, glucose-6-dehydrogenase by glucose-6-P or TPN, pyruvate kinase by phosphoenolypyruvate or ADP, hexokinase by glucose, and fumarase by a mixture of fumarate and malate. Lactate dehdrogenase was not protected by either of its substrates of coenzymes. Citrate synthase was probably protected by oxalacetate. Our data suggest that the protease or proteases discussed here may participate in the inactivation or degradation of a least some enzymes in Tetrahymena. Since the inactivation occurs at neutral pH, this process could be regulated by variations in the cellular levels of substrates, coenzymes, or allosteric regulators resulting form changes in growth conditions or growth state. Such a mechanism would permit the selective retention of enzymes of metabolically active pathways.
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PMID:Enzyme inactivation by a cellular neutral protease: enzyme specificity, effects of ligands on inactivation, and implications for the regulation of enzyme degradation. 1 68

Aconitase and NAD linked isocitrate dehydrogenase were present in Ascaris lumbricoides muscle at only very low activities, whilst there were significant levels of citrate synthase, NADP linked isocitrate dehydrogenase, 2-oxoglutarate dehydrogenase and succinic thiokinase. Pyruvate dehydrogenase was present in A. lumbricoides muscle at levels comparable with mammalian tissues and results suggest that it is modulated via a phosphotransferase/phosphatase system. The tricarboxylic acid cycle intermediates, citrate, isocitrate and 2-oxoglutarate were all detected in freeze clamped muscle, but their steady state levels were considerably lower than those found in mammalian tissues.
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PMID:Pyruvate and citrate metabolism in the muscle tissue of Ascaris lumbricoides. 2 88

2-Methylcitrate was tested in vitro on enzymes which interact with citrate and isocitrate. It was found to inhibit citrate synthase, aconitase, the NAD+- and NADP+-linked isocitrate dehydrogenase. This inhibition was competitive in nature except in the case of aconitase, and the Ki for all the enzymes was in the range of 1.5-7.6 mM. Phosphofructokinase was also inhibited by 2-methylcitrate with 50% inhibition achieved at 1 mM. ATP-citrate lyase and acetyl-CoA carboxylase were not inhibited by this compound. 2-Methylcitrate was not a substrate for ATP-citrate lyase. Acetyl-CoA carboxylase was activated by 2-methylcitrate with a Ka of 2.8 mM. The apparent Km (3.3 mM) for 2-methylcitrate for the mitochondrial citrate transporter was about 10-fold higher than the apparent Km (0.26 mM) for citrate. The tricarboxylase carrier can also be inhibited by low concentrations (0.2 mM) of 2-methylcitrate when the concentration of citrate is close to the apparent Km. Accumulation of 2-methylcitrate inside the mitochondrion, therefore, might lead to inhibition of enzymes in the citric acid cycle and thereby contribute to the ketogenesis and hypoglycemia seen under these conditions.
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PMID:Effect of 2-methylcitrate on citrate metabolism: implications for the management of patients with propionic acidemia and methylmalonic aciduria. 12 73

Peroxisomes were isolated form derepressed (lactose grown) Saccharomyces cerevisiae cells following homogenization with a "Merkenschlager" cell mill (at 0 degrees C using glass beads). Catalase and urate oxidase, along with low activities of D-amino acid oxidase and L-alpha-hydroxyacid oxidase (glycollate oxidase), were associated with the peroxisomes. No catalase activity was present in glucose repressed cells. When protoplasts prepared from derepressed cells were used for peroxisome isolation, catalase activity was not sedimentable through gradients. Apparently peroxisomes were destroyed as the cells became fermentative during protoplast preparation. The distribution of glyoxylate cycle enzymes was examined. Isocitrate lyase was not sedimentable, suggesting that, if the enzyme is peroxisome-associated, it is either readily released of present in a labile second class of peroxisomes. Low activities of malate dehydrogenase and citrate synthetase were found in peroxisome fractions from gradients, but may represent mitochondrial contamination. Citrate synthetase was not found associated with a low-density particle as had been previously reported.
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PMID:The isolation and characterization of peroxisomes (microbodies) from baker's yeast, Saccharomyces cerevisiae. 24 96

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

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

Cultures of isocitrate dehydrogenase-deficient (icd) mutants were overgrown by double mutants (icd glt) lacking citrate synthase activity also. The icd mutants grew more slowly than wild-type cells or the double mutants because they accumulated an inhibitory metabolite (possibly citrate). Intracellular citrate levels were several hundred-fold higher in icd cells than in wild-type or icd glt cells. Final growth yields of the wild type and the icd mutant on limiting glucose were equivalent and greater than the growth yield of icd glt double mutants. The icd gene mapped between 60 and 74 min. icd mutants were resistant to nalidixic acid, but glt and icd glt mutants and wild-type cells were sensitive, indicating that resistance results from accumulation of isocitrate, citrate, or a derivative of these compounds.
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PMID:Selection for citrate synthase deficiency in icd mutants of Escherichia coli. 77 50

Cell-free extracts of Rickettsia typhi were tested for activities of enzymes of the tricarboxylic acid cycle, of glutamate catabolism, and of glycolysis. The organisms were grown in the yolk sacs of chicken embryos, harvested shortly before the time of embryo death, purified by Renografin density gradient centrifugation, and ruptured in a French pressure cell. The following enzymatic activities were demonstrated: high levels of malate dehydrogenase (MDH), moderate levels of glutamate-oxaloacetate transaminase, glutamate, succinate, and isocitrate dehydrogenases, and citrate synthase, and low levels of glutamate-pyruvate transaminase. The specific activities of some of these enzymes were higher when the rickettsiae were harvested at a time of active proliferation, 3 to 4 days prior to embryo death. Rickettsial MDH was differentiated from host MDH by its migration pattern on polyacrylamide gel electrophoresis. The activities of MDH and two other dehydrogenases, demonstrable after the cells had been disrupted, were absent from purified, intact rickettsial preparations. No activity was detected for glucose-6-phosphate, 6-phosphogluconate, glyceraldehyde-3-phosphate, lactate dehydrogenases, phosphoglucose isomerase, fructoaldolase, or pyruvate kinase. Our results suggest that extracts of R. typhi that contain demonstrable enzymes involved in the catabolism of glutamate and tricarboxylic acid cycle intermediates, unlike Coxiella burnetti, lack detectable glycolytic activity.
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PMID:Enzymatic activities of cell-free extracts of Rickettsia typhi. 82 Jun 44


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