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)

Azotobacter beijerinckii was grown in ammonia-free glucose/mineral salts media in chemostat culture under oxygen or nitrogen limitation. Selected enzymes of the tricarboxylic acid cycle and poly-beta-hydroxybutyrate metabolism were monitored in relation to oxygen supply for both steady and transition states. Two dissolved oxygen concentrations were used for the nitrogen-limited steady state to investigate the possible effects of respiratory protection of nitrogenase on these enzymes. The levels of NADH oxidase, isocitrate dehydrogenase and 2-oxoglutarate dehydrogenase increased markedly on relaxation of oxygen limitation while pyruvate dehydrogenase and citrate synthase were relatively unaffected. beta-Ketothiolase and acetoacetyl-CoA reductase levels decreased as oxygen limitation was relaxed. Respiratory activity, as measured by the QO2 value, increased with oxygen supply rate. Imposition of oxygen limitation on a nitrogen-limited culture caused an immediate increase in the NADH/NAD ratio but this rapidly readjusted to its previous steady-state value. These changes are discussed in relation to respiratory protection of nitrogenase and poly-beta-hydroxybutyrate metabolism in A. beijerinckii.
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PMID:Regulation of the tricarboxylic acid cycle and poly-beta-hydroxybutyrate metabolism in Azotobacter beijerinckii grown under nitrogen or oxygen limitation. 1 43

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

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

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 mitochondrial matrix subfractions from rat liver, kidney cortex, brain, heart, and skeletal muscle were isolated and their protein components were resolved by two-dimensional polyacrylamide gel electrophoresis, revealing between 120 and 150 components for each matrix subfraction. Excellent resolution was obtained utilizing a pH 5 to 8 gradient in the first dimension and in 8 to 13% exponential acrylamide gradient in the second dimension, increasing the number of mitochondrial matrix proteins observed 3-fold over one-dimensional systems. Protein components tentatively identified by co-migration with pure enzymes and by known tissue distributions are carbamoyl-phosphate synthetase (EC 2.7.2.5), ornithine transcarbamylase (EC 2.1.3.3), glutamate dehydrogenase (EC 1.4.1.3), pyruvate carboxylase (EC 6.4.1.1), citrate synthase (EC 4.1.3.7), fumarase (EC 4.2.1.2), aconitase (EC 4.2.1.3), alpha-ketoglutarate dehydrogenase (EC 1.2.4.2), dihydrolipoyl transsuccinylase (EC 2.3.1.12), lipoamide dehydrogenase (EC 1.6.4.3), glutamate-aspartate aminotransferase (EC 2.6.1.1), and the two subunits of pyruvate dehydrogenase (EC 1.2.4.1). Protein components unambiguously identified by peptide mapping are citrate synthase, aconitase, and pyruvate carboxylase. The inner membrane subfraction from rat liver mitochondria was also resolved two dimensionally; the alpha and beta subunits of ATPase (F1) (EC 3.6.1.3) were identified by peptide mapping.
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PMID:Resolution of rat mitochondrial matrix proteins by two-dimensional polyacrylamide gel electrophoresis. 44 63

alpha-Ketoglutarate: glyoxylate carboligase activity has been reported by other laboratories to be present in mitochondria and in the cytosol of mammalian tissues; the mitochondrial activity is associated with the alpha-ketoglutarate decarboxylase moiety of the alpha-ketoglutarate dehydrogenase complex. The cellular distribution of the carboligase has been re-examined here using marker enzymes of known localization in order to monitor the composition of subcellular fractions prepared by differential centrifugation. Carboligase activity paralleled the activity of the mitochondrial matrix enzyme citrate synthase in subcellular fractions prepared from rat liver, heart and brain as well as from rabbit liver. Whole rat liver mitochondria upon lysis released both carboligase and citrate synthase. The activity patterns of several other extramitochondrial marker enzymes differed significantly from that of carboligase in rat liver. In addition, the distribution pattern of carboligase was similar to that of alpha-ketoglutarate decarboxylase and of alpha-ketoglutarate dehydrogenase complex. The data indicate that alpha-ketoglutarate: glyoxylate carboligase activity is located exclusively within the mitochondria of the rat and rabbit tissues investigated. There is no evidence for a cytosolic form of the enzyme. Thus the report from other laboratory that the molecular etiology of the human genetic disorder hyperoxaluria type I is a deficiency of cytosolic carboligase must be questioned.
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PMID:Cellular localization of alpha-ketoglutarate: glyoxylate carboligase in rat tissues. 91 88

The occurrence and levels of activity of various enzymes of carbohydrate catabolism in culture forms (promastigotes) of 4 human species of Leishmania (L. brasiliensis, L. donovani, L. mexicana, and L. tropica) were compared. These organisms possess enzymes of the Embden-Meyerhof pathway but lack lactate dehydrogenase. No evidence could be found for the production of lactic acid by growing cultures and lactic acid could not be detected either in cell-free preparations or after incubation of cell-free extracts with pyruvate and NADH under appropriate conditions. All 4 species possess alpha-glycerophosphate dehydrogenase and alpha-glycerophosphate phosphatase which together could regenerate NAD, thus compensating for the absence of lactate dehydrogenase. The oxidative and nonoxidative reactions of the hexose monophosphate pathway are present in all 4 species. Cell-free extracts have pyruvate dehydrogenase activity which allows the entry of pyruvate into and its subsequent oxidation through the tricarboxylic acid cycle. All enzymes of this cycle, including a thiamine pyrophosphate dependent alpha-ketoglutarate dehydrogenase, are present. Both NAD and NADP-linked malate dehydrogenase activities are present. The isocitrate dehydrogenase is NADP specific. There is an active glutamate dehydrogenase which could compete with alpha-ketoglutarate dehydrogenase for the common substrate (alpha-ketoglutarate). Replenishment of C4 acids is accomplished by heterotrophic CO2 fixation catalyzed by pyruvate carboxylase. All 4 species have high levels of NADH oxidase activity. Several enzymes thus far not found in any species of Leishmania have been demonstrated. These are: phosphoglucose isomerase, triose phosphate isomerase, fructose-1, 6-diphosphatase, 3-phosphoglycerate kinase, enolase, alpha-glycerophosphate dehydrogenase, alpha-glycerophosphate phosphatase, pyruvate dehydrogenase complex, citrate synthase, aconitase, alpha-ketoglutarate dehydrogenase, glutamate dehydrogenase, and NADH oxidase.
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PMID:Enzymes of carbohydrate metabolism in four human species of Leishmania: a comparative survey. 100 46

Carbon-14 was incorporated into oxalate and CO2 from either citrate-1,5-14C, succinate-1,4-14C, or fumarate-1,4-14C by cultures of Aspergillus niger pregrown on a medium which contained glucose as the sole carbon source and which did not allow citrate accumulation. In cell-free extracts of mycelium forming oxalate and CO2 from added citrate the following enzymes of the tricarboxylic acid (TCA) cycle were identified: citrate synthase CE 4.1.3.7), aconitate hydratase (EC4.2.1.3), NAD and NADP-dependent isocitrate dehydrogenase (EC 1.1.1.41, 1.1.1.42), (alpha-oxoglutarate dehydrogenase (EC 1.2.4.2), succinate dehydrogenase (EC 1.3.99.1), fumarate hydratase (EC 4.2.1.2), and malate dehydrogenase (EC 1.1.1.37). The in vitro activity of aconitate hydratase and of NADP-dependent isocitrate dehydrogenase was shown to be almost identical to the rate of in vivo degradation of citrate or to exceed this rate. The degradation of citrate to oxalate was inhibited completely by 9 mM fluoroacetate. It is concluded that the TCA cycle is involved in the formation of oxalate from citrate.
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PMID:Oxalate accumulation from citrate by Aspergillus niger. II. Involvement of the tricarboxylic acid cyclase. 115

Feedback control between flux through the phosphorylating electron transport chain and the coordination of flux through individual steps of the citric acid cycle have been investigated under a number of different conditions of substrate availability and workloads in the isolated perfused rat heart. The transition from substrate-free perfusion to perfusion with glucose and insulin with no change of workload was associated with increases in the pool sizes of citric acid cycle intermediates except for oxaloacetate, but with an initial imbalance of flux through individual steps in the cycle and transport of anions of the malate-aspartate cycle across the mitochondrial membrane. Flux through citrate synthase initially increased while that through alpha-ketoglutarate dehydrogenase decreased. Of the components of the malate-aspartate cycle, flux through the malate-alpha-ketoglutarate exchange was increased prior to that through the glutamate-aspartate exchange and intramitochondrial aspartate aminotransferase. These changes can be accounted for on the basis of known kinetic controls of the enzyme and transport steps in response to increased pyruvate, acetyl-CoA, and NADH delivery at an approximately constant rate of ATP turnover.
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PMID:Coordination of citric acid cycle activity with electron transport flux. 126 91

The level of aspartate aminotransferase in liver mitochondria was found to be approximately 140 microM, or 2-3 orders of magnitude higher than its dissociation constant in complexes with the inner mitochondrial membrane and the high molecular weight enzymes (M(r) = 1.6 x 10(5) to 2.7 x 10(6)) carbamyl-phosphate synthase I, glutamate dehydrogenase, and the alpha-ketoglutarate dehydrogenase complex. The total concentration of aminotransferase-binding sites on these structures in liver mitochondria was more than sufficient to accommodate all of the aminotransferase. Therefore, in liver mitochondria, the aminotransferase could be associated with the inner mitochondrial membrane and/or these high molecular weight enzymes. The aminotransferase in these hetero-enzyme complexes could be supplied with oxalacetate because binding of aminotransferase to the high molecular weight enzymes can enhance binding of malate dehydrogenase, and binding of both malate dehydrogenase and the aminotransferase facilitated binding of fumarase. The level of malate dehydrogenase was found to be so high (140 microM) in liver mitochondria, compared with that of citrate synthase (25 microM) and the pyruvate dehydrogenase complex (0.3 microM), that there would also be a sufficient supply of oxalacetate to citrate synthase-pyruvate dehydrogenase.
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PMID:Glutamate-malate metabolism in liver mitochondria. A model constructed on the basis of mitochondrial levels of enzymes, specificity, dissociation constants, and stoichiometry of hetero-enzyme complexes. 135 Feb 79


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