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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)

Spheroplast membranes (spheroplast envelopes) of strain 2091 of group B Neisseria meningitidis were prepared by a procedure that included lysozyme treatment of the cells and osmotic lysis of the resulting spheroplasts. Electron microscopy revealed that the membranes consisted of two unit layers, generally parallel to each other. The membrane preparation migrated as a single component in a 40 to 70% sucrose gradient and consisted of 62% protein, 28% lipid, 9% ribonucleic acid, small amounts of carbohydrate, hexosamine, and deoxyribonucleic acid. When 1 or 10 mug (dry weight) was injected intravenously into rabbits, a mild pyrogenic reaction was elicited. In immunodiffusion tests, immune rabbit serum prepared against spheroplast membranes produced three major precipitin lines, with the homologous antigen solubilized with sodium dodecyl sulfate, and a single line with untreated antigen. The immune serum also reacted with a cell wall antigen, and to a lesser extent with some of the cytoplasmic antigens. Succinate dehydrogenase and reduced nicotinamide adenine dinucleotide (NADH) oxidase activities were found to be associated with the spheroplast membranes. NADH dehydrogenase also was associated with the membranes but was gradually released and recovered in other fractions. Glutamate-oxaloacetate transaminase, glutamate, glucose-6-phosphate, and isocitrate dehydrogenase activities were not found in the membrane preparation. About one-third of these enzymatic activities were recovered in the supernatant fluid after the sedimentation of the spheroplasts and two-thirds were recovered in the cytoplasmic fraction. N-acetylneuraminic acid (NAN)-condensing enzyme and cytidine monophosphate-NAN synthesizing enzyme also were identified in this organism. These enzymes were not associated with the membranes and were recovered from extracts from whole cells, spheroplasts, or cells exposed to osmotic shock, as well as from spheroplast supernatant and shock fluids. It is concluded that the spheroplast membranes of the strain of meningococci used in these studies are typical of those recovered from gram-negative bacteria.
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PMID:Characterization of spheroplast membranes of Neisseria meningitidis group B. 463 Jul 22

Acetohydroxy acid synthetase, which is sensitive to catabolite repression in wild-type Escherichia coli B, was relatively resistant to this control in a streptomycin-dependent mutant. The streptomycin-dependent mutant was found to be inducible for beta-galactosidase in the presence of glucose, although repression of beta-galactosidase by glucose occurred under experimental conditions where growth of the streptomycin-dependent mutant was limited. Additional glucose-sensitive enzymes of wild-type E. coli B (citrate synthase, fumarase, aconitase and isocitrate dehydrogenase) were found to be insensitive to the carbon source in streptomycin-dependent mutants: these enzymes were formed by streptomycin-dependent E. coli B in equivalent quantities when either glucose or glycerol was the carbon source. Two enzymes, glucokinase and glucose 6-phosphate dehydrogenase, that are glucose-insensitive in wild-type E. coli B were formed in equivalent quantity on glucose or glycerol in both streptomycin-sensitive and streptomycin-dependent E. coli B. The results indicate a general decrease or relaxation of catabolite repression in the streptomycin-dependent mutant. The yield of streptomycin-dependent cells from glucose was one-third less than that of the streptomycin-sensitive strain. We conclude that the decreased efficiency of glucose utilization in streptomycin-dependent E. coli B is responsible for the relaxation of catabolite repression in this mutant.
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PMID:Relaxation of catabolite repression in streptomycin-dependent Escherichia coli. 497 19

The growth response of Listeria monocytogenes strains A4413 and 9037-7 to carbohydrates was determined in a defined medium. Neither pyruvate, acetate, citrate, isocitrate, alpha-ketoglutarate, succinate, fumarate, nor malate supported growth. Furthermore, inclusion of any of these carbohydrates in the growth medium with glucose did not increase the growth of Listeria over that observed on glucose alone. Resting cell suspensions of strain A4413 oxidized pyruvate but not acetate, citrate, isocitrate, alpha-ketoglutarate, succinate, fumarate, or malate. Cell-free extracts of strain A4413 contained active citrate synthase, aconitate hydratase, isocitrate dehydrogenase, malate dehydrogenase, fumarate hydratase, fumarate reductase, pyruvate dehydrogenase system, and oxidases for reduced nicotinamide adenine dinucleotide and reduced nicotinamide adenine dinucleotide phosphate. The alpha-ketoglutarate oxidation system, succinate dehydrogenase, isocitrate lyase, and malate synthase were not detected. Cytochromes were not detected. The data suggest that strain A4413, under these conditions, utilizes a split noncyclic citrate pathway which has an oxidative portion (citrate synthase, aconitate hydratase, and isocitrate dehydrogenase) and a reductive portion (malate dehydrogenase, fumarate hydratase, and fumarate reductase). This pathway is probably important in biosynthesis but not for a net gain in energy.
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PMID:Citrate cycle and related metabolism of Listeria monocytogenes. 499 14

1. Transient and steady-state changes caused by acetate utilization were studied in perfused rat heart. The transient period occupied 6min and steady-state changes were followed in a further 6min of perfusion. 2. In control perfusions glucose oxidation accounted for 75% of oxygen utilization; the remaining 25% was assumed to represent oxidation of glyceride fatty acids. With acetate in the steady state, acetate oxidation accounted for 80% of oxygen utilization, which increased by 20%; glucose oxidation was almost totally suppressed. The rate of tricarboxylate-cycle turnover increased by 67% with acetate perfusion. The net yield of ATP in the steady state was not altered by acetate. 3. Acetate oxidation increased muscle concentrations of acetyl-CoA, citrate, isocitrate, 2-oxoglutarate, glutamate, alanine, AMP and glucose 6-phosphate, and lowered those of CoA and aspartate; the concentrations of pyruvate, ATP and ADP showed no detectable change. The times for maximum changes were 1min, acetyl-CoA, CoA, alanine and AMP; 6min, citrate, isocitrate, glutamate and aspartate; 2-4min, 2-oxoglutarate. Malate concentration fell in the first minute and rose to a value somewhat greater than in the control by 6min. There was a transient and rapid rise in glucose 6-phosphate concentration in the first minute superimposed on the slower rise over 6min. 4. Acetate perfusion decreased the output of lactate, the muscle concentration of lactate and the [lactate]/[pyruvate] ratio in perfusion medium and muscle in the first minute; these returned to control values by 6min. 5. During the first minute acetate decreased oxygen consumption and lowered the net yield of ATP by 30% without any significant change in muscle ATP or ADP concentrations. 6. The specific radioactivities of cycle metabolites were measured during and after a 1min pulse of [1-(14)C]acetate delivered in the first and twelfth minutes of acetate perfusion. A model based on the known flow rates and concentrations of cycle metabolites was analysed by computer simulation. The model, which assumed single pools of cycle metabolites, fitted the data well with the inclusion of an isotope-exchange reaction between isocitrate and 2-oxoglutarate+bicarbonate. The exchange was verified by perfusions with [(14)C]bicarbonate. There was no evidence for isotope exchange between citrate and acetyl-CoA or between 2-oxoglutarate and malate. There was rapid isotope equilibration between 2-oxoglutarate and glutamate, but relatively poor isotope equilibration between malate and aspartate. 7. It is concluded that the citrate synthase reaction is displaced from equilibrium in rat heart, that isocitrate dehydrogenase and aconitate hydratase may approximate to equilibrium, that alanine aminotransferase is close to equilibrium, but that aspartate transamination is slow for reasons that have yet to be investigated. 8. The slow rise in citrate concentration as compared with the rapid rise in that of acetyl-CoA is attributed to the slow generation of oxaloacetate by aspartate aminotransferase. 9. It is proposed that the tricarboxylate cycle may operate as two spans: acetyl-CoA-->2-oxoglutarate, controlled by citrate synthase, and 2-oxoglutarate-->oxaloacetate, controlled by 2-oxoglutarate dehydrogenase; a scheme for cycle control during acetate oxidation is outlined. The initiating factors are considered to be changes in acetyl-CoA, CoA and AMP concentrations brought about by acetyl-CoA synthetase. 10. Evidence is presented for a transient inhibition of phosphofructokinase during the first minute of acetate perfusion that was not due to a rise in whole-tissue citrate concentration. The probable importance of metabolite compartmentation is stressed.
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PMID:Control of the tricarboxylate cycle and its interactions with glycolysis during acetate utilization in rat heart. 544 22

The levels of Krebs cycle, glyoxylate cycle, and certain other enzymes were measured in a wild-type strain and in seven groups of acetate-nonutilizing (acu) mutants of Neurospora crassa, both after growth on a medium containing sucrose and after a subsequent 6-hr incubation in a similar medium, containing acetate as the sole source of carbon. In the wild strain, incubation in acetate medium caused a rise in the levels of isocitrate lyase, malate synthase, phosphoenolpyruvate carboxykinase, acetyl-coenzyme A synthetase, nicotinamide adenine dinucleotide phosphate-linked isocitrate dehydrogenase, citrate synthase, and fumarate hydratase. Isocitrate lyase activity was absent in acu-3 mutants; acu-5 mutants lacked acetyl-coenzyme A synthetase activity; and no oxoglutarate dehydrogenase activity (or only low levels) could be detected in acu-2 and acu-7 mutants. In acu-6 mutants, phosphoenolpyruvate carboxykinase activity was either very low or absent. No specific biochemical deficiencies could be attributed to the acu-1 and acu-4 mutations. The role of several of these enzymes during growth on acetate is discussed.
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PMID:Acetate-nonutilizing mutants of Neurospora rassa. II. Biochemical deficiencies and the roles of certain enzymes. 564 48

The activities of the eight citric acid-cycle enzymes of rat bone-marrow cells were determined along with several other mitochondrial and non-mitochondrial enzymes. Four of the citric acid-cycle enzymes (aconitase, succinyl-CoA thiokinase, alpha-oxoglutarate dehydrogenase and succinate dehydrogenase) have closely similar low activities; two [isocitrate dehydrogenase (NAD) and citrate synthase] have intermediate activities; the remaining two (malate dehydrogenase and fumarase) have high activities. The other enzymes surveyed also exhibited a spread of three orders of magnitude, the mitochondrial enzymes showing no less variation than the others.
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PMID:The activities of the citric acid-cycle enzymes in rat bone-marrow cells. 566 55

Acetate oxidation by sulphate was studied with desulfobacter postgatei. Cell extracts of the organism were found to contain high activities of the following enzymes: citrate synthase, aconitase, isocitrate dehydrogenase, alpha-ketoglutarate dehydrogenase, succinate dehydrogenase, fumarase, malate dehydrogenase and pyruvate synthase. It is concluded that acetate oxidation with sulphate in D. postgatei proceeds via the citric acid cycle with the synthesis of pyruvate from acetyl CoA and CO2 as an anaplerotic reaction. The apparent Ks for acetate oxidation by D. postgatei as determined in vivo was near 0.2 mM. The apparent Ks for acetate fermentation to methane and CO2 by methanosarcina barkeri was 3 mM. The significantly lower ks for acetate of the sulphate reducer explains why methane formation from acetate in natural habitats is apparently inhibited by sulphate.
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PMID:Dissimilatory sulphate reduction with acetate as electron donor. 612 36

Aldosterone-dependent changes in citrate synthase (CS) activity have been used as an index of mineralocorticoid target sites. However, adrenalectomy (ADX) resulted in a fall in activity of CS and several other enzymes in rabbit heart, a tissue with glucocorticoid-but not mineralocorticoid-specific receptors. The enzymes included CS (2.03-1.36 U/mg protein, normal----ADX, P less than 0.001), isocitrate dehydrogenase-NADP+ (1.10-0.80 U/mg, P less than 0.002), isocitrate dehydrogenase-NAD+ (0.034-0.020 U/mg, P less than 0.01), and hydroxymethylglutaryl-CoA lyase (0.072 to 0.035 U/mg, P less than 0.001); in contrast, mitochondrial malate dehydrogenase levels were not significantly reduced by adrenal loss. There was also a decrease after surgery in sarcolemmal Na-K-(17.30-12.31 mumol Pi . mg protein-1 . h-1, P less than 0.002) and Mg-ATPase activities (14.16-12.11 mumol Pi . mg protein-1 . h-1, P less than 0.05). However, ADX did not result in a significant change in heart weight per kilogram body weight or recovery of mitochondrial protein per gram heart. CS was also assayed in hearts from ADX animals following acute (90 min) and chronic (3 day) steroid replacement. Although neither acute intravenous aldosterone (10 micrograms/kg) nor dexamethasone (100 micrograms/kg) increased activity, exposure to multiple subcutaneous injections of either steroid over a 3-day period significantly elevated CS above ADX values. The coordinate changes in the levels of several myocardial enzymes associated with energy metabolism is discussed in terms of an adaptation to chronic alterations in energy demands as opposed to specific mineralocorticoid or glucocorticoid receptor-mediated processes.
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PMID:Influence of adrenalectomy and steroid replacement on heart citrate synthase levels. 614 77

A mathematical model was used to study the role of various allosteric regulatory mechanisms in the oxidation of glucose and fatty acids by muscle energy metabolism. A large number of such mechanisms were shown to be involved in simultaneous oxidation of both substrates: glycolysis is regulated by the ATP/ADP ratio at the phosphofructokinase (PFK) step; the control over pyruvate dehydrogenase is exercised by the NADHm/NADm+ and CoAsAc/CoAsH ratios as well as by the level of pyruvate; the Krebs cycle is regulated by oxaloacetate and citrate concentrations in the citrate synthase reaction and by the ATP/ADP and NADHm/NADm+ ratios in the isocitrate dehydrogenase reaction. The inhibition of PFK and pyruvate dehydrogenase by excess of CoAsAcyl as well as the inhibition of PFK by citrate are additional equivalent regulatory mechanisms. When glucose alone is oxidized, the levels of citrate, CoAsAcyl, NADHm and CoAsAc decrease drastically within the whole range of physiological ATPase loads; the only regulating factors that remain efficient are the ATP/ADP ratio in glycolysis, the level of pyruvate at the pyruvate dehydrogenase step, the ATP/ADP ratio and the levels of CoAsAc, oxaloacetate and isocitrate in the Krebs cycle.
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PMID:[Mechanisms of the regulation of muscle energy metabolism on oxidation of glucose and fatty acids. A mathematical model]. 621 68

The activities of citrate synthase, NAD-isocitrate dehydrogenase and 2-oxoglutarate dehydrogenase were measured in homogenates of soleus, diaphragm and heart muscles of the rat, in an attempt to define potential tricarboxylate cycle activity and its response to aging. Activities were significantly decreased in 24-month animals versus 6-month controls in every case (except 2-oxoglutarate dehydrogenase in heart muscle). Age-linked decrements were greatest in the soleus and least in heart. Cytochrome oxidase was measured as an index of total respiratory chain activity and decreased significantly in each case, with the smallest decrease in the heart. Acyl-CoA dehydrogenase and 3-hydroxyacyl-Co-A dehydrogenase were measured as an index of beta-oxidative activity; the former decreased in soleus and diaphragm, the latter in soleus and heart, with the decrease in the soleus being the greater. Carnitine acetyl- and palmitoyltransferases were measured, together with the muscle content of carnitine and acylcarnitine, as determining the potential rate of entry of acyl groups into the mitochondria for oxidation. Carnitine acetyltransferase activity was decreased with age in each of the muscles, but to the greatest extent in the heart. Carnitine palmitoyltransferase was decreased in both soleus and diaphragm. Carnitine content was decreased most in the soleus and the heart and to a lesser extent in the diaphragm. It is concluded that there is a generalized decline in oxidative activity in all of these muscles with age, on the basis of wet weight; this occurs to the greatest extent in the soleus and to the least extent in the heart. There is, in addition, a specific deficiency in the ability to oxidize fatty acids, relative to other substrates, in heart muscle.
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PMID:Age-linked changes in the activity of enzymes of the tricarboxylate cycle and lipid oxidation, and of carnitine content, in muscles of the rat. 628 24


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