Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: EC:2.3.3.1 (citrate synthase)
 4,488 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Citrate synthase activity of Saccharomyces cerevisiae was determined by a radioactive assay procedure and the reaction product, 14C-citric acid, was identified by chromatographic techniques. ATP, d-ATP, GTP and NADH were most inhibitory to the citrate synthase invitro. The activity was inhibited to a lesser extent by ADP, UTP, and NADP whereas, AMP and CTP were much less inhibitory. NADH, like NAD, glutamic acid, glutamine, arginine, ornithine, proline, aspartic acid and alpha-ketoglutarate exhibited no inhibition. These results have been discussed in the light of the role of citrate synthase for the energy metabolism and glutamic acid biosynthesis.
 ...
PMID:Regulation of citrate synthase activity of Saccharomyces cerevisiae. 0

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.
 ...
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

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.
 ...
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.
 ...
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 mechanism of the massive extracellular production of citric and isocitric acids by Saccharomycopsis lipolytica grown on n-paraffins has been studied. When growth stops, because of nitrogen limitation, the intracellular concentration of ATP sharply rises whereas that of AMP and ADP decreases to a low level. At the same time production of acids begins. The activity of the NAD-dependent isocitrate dehydrogenase which requires AMP for activity becomes very low and prevents the oxidative function of the citric acid cycle whereas isocitrate lyase is not inhibited. As citrate synthase inhibition by ATP appears to be insufficient to stop n-paraffin degradation, citric and isocitric acids accumulation can take place. Massive excretion of these acids, however, probably still involves other physiological changes brought about by nitrogen limitation, possibly some permeabilization of the cell to these acids.
 ...
PMID:Regulation of the central metabolism in relation to citric acid production in Saccharomycopsis lipolytica. 88 90

Alkylation of ATP with iodoacetic acid at pH 6.5 yielded 1-carboxymethyl-ATP which, after alkaline rearrangement, gave N-6-carboxymethyl-ATP. Condensation of this analogue with 1,6-diaminohexane in the presence of a water-soluble carbodiimide generated N-6-[(6-aminohexyl)carbamoylmethyl]-ATP in an overall yield of 40% based on the parent nucleotide ATP. The coenzymic activities of both N-6-adenine-substituted derivatives of ATP were tested with three kinases. Both derivatives showed coenzymic function against hexokinase with the "long" derivative having highest activity (95%) relative to unsubstituted ATP. Their activities towards the other two kinases tested was negligible except with the "long" analogue against glycerokinase (20%). The latter ATP analogue, when bound to Sepharose through its terminal amino group, could be dephosphorylated to the corresponding ADP analogue with soluble hexokinase yielding glucose 6-phosphate in an enzymic "solidphase" fashion. The Sepharose-bound ADP formed could subsequently be phosphorylated back to ATP using soluble acetate kinase. Sepharose-ATP preparations were also used in preliminary affinity chromatography studies using citrate synthase. Alkylation of ADP following the above procedure yielded the corresponding ADP analogue, N-6-[(6-aminohexyl)carbamoylmethyl]-ADP in an overall yield of 40%. Alkylation of AMP yielded the corresponding N-6-[(6-aminohexyl)carbamoylmethyl]-AMP in an overall yield of 45%.
 ...
PMID:Preparation of analogues of ATP, ADP and AMP suitable for binding to matrices and the enzymic interconversion of ATP and ADP in solid phase. 114 Jan 97

The steady state mitochondrial content of coenzyme A-SH (CoA), acetyl-CoA, succinyl-CoA, and long chain acyl-CoA has been determined during the oxidation of palmitoylcarnitine by rabbit heart mitochondria. Variation of the substrate concentration during ADP-stimulated (state 3) respiration varies the mitochondrial content of long chain acyl-CoA and the rate of O2 uptake, and permits the conclusion that the Km of beta oxidation for intramitochondrial long chain acyl-CoA is approximately 1 nmol/mg of mitochondrial protein. At near saturating concentrations of palmitoylcarnitine, plus L-malate, the addition of ADP causes a decrease in acetyl-CoA, an increase in CoA and succinyl-CoA, and no clear change in long chain acyl-CoA content. These changes reverse upon the depletion of ADP (state 3 leads to 4 transition). Similar changes in CoA, acetyl-CoA, and succinyl-CoA are seen during state 4 leads to 3 leads to 4 transitions with pyruvate plus L-malate and octanoate plus L-malate as substrates. These results suggest a limitation of flux by citrate synthase during the controlled oxidation of these three substrates. The ratio acetyl-CoA/succinyl-CoA was determined not only during state 3 and state 4 oxidation of palmitoylcarnitine plus L-malate and pyruvate plus L-malate, but also during intermediate respiratory states (state 3 1/2) generated by adding glucose and varying amounts of hexokinase. These intermediate states are characterized by a high succinyl-CoA content, relative to either state 3 or state 4, and a suboptimal flux through citrate synthase, estimated either by pyruvate disappearance or by O2 uptake.
 ...
PMID:The steady state concentrations of coenzyme A-SH and coenzyme A thioester, citrate, and isocitrate during tricarboxylate cycle oxidations in rabbit heart mitochondria. 119 59

The synthesis of ketone bodies by intact isolated rat-liver mitochondria has been studied at varying rates of acetyl-CoA production and of acetyl-CoA utilization in the Krebs cycle. Factors which enhanced the rate of acetyl-CoA production caused an increase in the fraction of acetyl-CoA which was incorporated into ketone bodies. On the other hand, it was found that factors which stimulated the formation of citrate lowered the relative rate of ketogenesis. It is concluded that acetyl-CoA is preferentially used for citrate synthesis, if the level of oxaloacetate in the mitochondrial matrix space is adequate. The intramitochondrial level of oxaloacetate, which is determined by the malate concentration and the ratio of NADH over NAD+, is the main factor controlling the rate of citrate synthesis. The ATP/ADP ratio per se does not affect the activity of citrate synthase in this in vitro system. Ketogenesis can be described as an overflow of acetyl-groups: Ketone-body formation is stimulated only when the rate of acetyl-CoA production increases beyond the capacity for citrate synthesis. The interaction between fatty acid oxidation and pyruvate metabolism and the effects of long-chain acyl-CoA on mitochondrial metabolism are discussed. Ketone bodies which were generated during the oxidation of [1-14C] fatty acids were preferentially labelled in their carboxyl group. This carboxyl group had the same specific activity as the acetyl-CoA pool, whereas the specific activity of the acetone moiety of acetoacetate was much lower, especially at low rates of ketone-body formation. The activities of acetoacetyl-CoA deacylase and the hydroxymethylglutaryl-CoA (HMG-CoA) pathway were compared in soluble and mitochondrial fractions of rat- and cow-liver in different ketotic states. In rat-liver mitochondria, both pathways of acetoacetate synthesis were stimulated upon starvation or in alloxan diabetes. In cow liver, only the HMG-CoA pathway was increased during ketosis in the mitochondrial as well as in the soluble fraction.
 ...
PMID:Aspects of ketogenesis: control and mechanism of ketone-body formation in isolated rat-liver mitochondria. 119 5

The structural gene coding for citrate synthase from the gram-positive soil isolate Bacillus sp. strain C4 (ATCC 55182) capable of secreting acetic acid at pH 5.0 to 7.0 in the presence of dolime has been cloned from a genomic library by complementation of an Escherichia coli auxotrophic mutant lacking citrate synthase. The nucleotide sequence of the entire 3.1-kb HindIII fragment has been determined, and one major open reading frame was found coding for citrate synthase (ctsA). Citrate synthase from Bacillus sp. strain C4 was found to be a dimer (Mr, 84,500) with a subunit with an Mr of 42,000. The N-terminal sequence was found to be identical with that predicted from the gene sequence. The kinetics were best fit to a bisubstrate enzyme with an ordered mechanism. Bacillus sp. strain C4 citrate synthase was not activated by potassium chloride and was not inhibited by NADH, ATP, ADP, or AMP at levels up to 1 mM. The predicted amino acid sequence was compared with that of the E. coli, Acinetobacter anitratum, Pseudomonas aeruginosa, Rickettsia prowazekii, porcine heart, and Saccharomyces cerevisiae cytoplasmic and mitochondrial enzymes.
 ...
PMID:Cloning and nucleotide sequence of the gene coding for citrate synthase from a thermotolerant Bacillus sp. 131 44

In order to evaluate the age dependency of enzymes involved in the energy-generating system, skeletal muscle specimens from rats of different ages were investigated for several mitochondrial enzymes. [1-14C]pyruvate (+/- ADP) oxidation rates and pyruvate dehydrogenase complex (PDHC) activity increased significantly from low early values during the neonatal period to nearly adult values at the end of the suckling period. Other enzymes of the pyruvate oxidation route such as citrate synthase and cytochrome c oxidase showed similar patterns of development. Immunoblot studies of PDHC detected a clear increase in the intensity of the bands of the alpha subunits of E1 (pyruvate dehydrogenase) and E2 (dihydrolipoyl transacetylase) within the first 3 weeks of life. The ratio between the individual PDHC proteins indicated that E1 alpha, the regulatory subunit of the multienzyme complex, is the most rapidly increasing protein with age.
 ...
PMID:Postnatal development of pyruvate oxidation in quadriceps muscle of the rat. 131 16


1 2 3 4 5 6 7 8 9 10 Next >>