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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)

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

Burton, Sheril D. (Institute of Marine Science, University of Alaska, College), Richard Y. Morita, and Wayne Miller. Utilization of acetate by Beggiatoa. J. Bacteriol. 91:1192-1200. 1966.-A proposed system which would permit acetate incorporation into four-carbon compounds without the presence of key enzymes of the citric acid cycle or glyoxylate cycle is described. In this system, acetyl-coenzyme A (CoA) is condensed with glyoxylate to form malate, which, in turn, is converted to oxaloacetate. Oxaloacetate then reacts with glutamate to produce alpha-ketoglutarate, which is subsequently converted to isocitrate. Cleavage of isocitrate produces glyoxylate and succinate. Thus, the proposed system is similar to the glyoxylate bypass in that malate is produced from glyoxylate and acetyl-CoA, but differs from both the citric acid cycle and the glyoxylate bypass, since citrate and fumarate are not involved. Fumarase, aconitase, catalase, citritase, pyruvate kinase, enolase, phosphoenolpyruvate carboxylase, lactic dehydrogenase, alpha-ketoglutarate dehydrogenase, and condensing enzyme were not detectable in crude extracts of Beggiatoa. Succinate was oxidized by a soluble enzyme not associated with an electron-transport particle. Isocitrate was identified as the sole compound labeled when C(14)O(2) was added to a reduced nicotinamide adenine dinucleotide, CO(2) generating system (crystalline glucose-6-phosphate dehydrogenase and glucose-6-phosphate) in the presence of alpha-ketoglutarate.
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PMID:Utilization of acetate by Beggiatoa. 592 51

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

Strain SF22, a glutamine-requiring (Gln-) mutant of Bacillus subtilis SMY, is likely to have a mutation in the structural gene for glutamine synthetase, since this strain synthesized 22 to 55% as much glutamine synthetase antigen as did wild-type cells in a 10-min period but had less than 3% of wild-type glutamine synthetase enzymatic activity. The expression of several genes subject to glucose catabolite repression was altered in the Gln- mutant. The induced levels of alpha-glucosidase, histidase, and aconitase were 3.5- to 4-fold higher in SF22 cells than in wild-type cells grown in glucose-glutamine medium, and citrate synthase levels were 8-fold higher in the Gln- mutant than in wild-type cells. The relief of glucose catabolite repression in the Gln- mutant may result from poor utilization of glucose. Examination of the intracellular metabolite pools of cells grown in glucose-glutamine medium showed that the glucose-6-phosphate pool was 2.5-fold lower, the pyruvate pool was 4-fold lower, and the 2-ketoglutarate pool was 2.5-fold lower in the Gln- cells than they were in wild-type cells. Intracellular levels of glutamine were sixfold higher in the Gln- mutant than in wild-type cells. Measurements of enzymes involved in glutamine transport and utilization showed that the elevated pools of glutamine in the Gln- mutant resulted from a threefold increase in glutamine permease and a fivefold decrease in glutamate synthase. The pleiotropic effect of the gln-22 mutation on the expression of several genes suggests that either the glutamine synthetase protein or its enzymatic product, glutamine, is involved in the regulation of several metabolic pathways in B. subtilis.
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PMID:Bacillus subtilis glutamine synthetase mutants pleiotropically altered in glucose catabolite repression. 614 Nov 56

The interaction of a novel fluorinated analogue of citrate, 3-fluoro-3-deoxycitrate (3-fluorocitrate), with the four known citrate-processing enzymes is described in this report. Three of the citrate-processing enzymes, citrate synthase, ATP citrate lyase, and citrate lyase, catalyze reversible aldol-type condensations. The fate of 3-fluorocitrate with each enzyme is uniquely related to their mechanisms of action. For citrate synthase, 3-fluorocitrate is a competitive inhibitor. 3-Fluorocitrate is a substrate for the carboxylate activation half-reaction catalyzed by ATP citrate lyase and induces a net ATPase action during conversion to 3-fluorocitryl-S-coenzyme A. Because of the unusual mechanism of citrate cleavage catalyzed by bacterial citrate lyase, 3-fluorocitrate is a mechanism-based inhibitor, acting at two points during turnover of the acetyl enzyme. The fourth citrate-processing enzyme, aconitase, does turn over 3-fluorocitrate catalytically. This enzyme, catalyzing a dehydration and rehydration of citrate, also catalyzes the elimination of HF from 3-fluorocitrate, yielding cis-aconitate and fluoride.
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PMID:3-fluoro-3-deoxycitrate: a probe for mechanistic study of citrate-utilizing enzymes. 621 36

Considerable variations were found in the in vitro effect of alloxan on mouse liver enzymes associated with the citric acid cycle. The following approximative alloxan concentrations induced 50% inhibition of enzyme activity: 10(-6)M for aconitase, 10(-4)M for NAD-linked isocitrate dehydrogenase, glutamate dehydrogenase, alpha-ketoglutarate dehydrogenase, succinyl-CoA synthetase and fumarase, and 10(-3)M for citrate synthase and NADP-linked isocitrate dehydrogenase. Pyruvate dehydrogenase, succinate dehydrogenase and malate dehydrogenase were not inhibited by 10(-3)M alloxan. The inhibition of aconitase was competitive both when using mouse liver and purified porcine heart enzyme. The Ki values for the purified enzyme in the presence of 5 microM alloxan were 0.22 microM with citrate, 4.0 microM with cis-aconitate and 0.62 microM with isocitrate as substrate. The high sensitivity of aconitase for inhibition by alloxan probably plays a prominent role for the toxic effects of alloxan.
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PMID:Inhibition by alloxan of mitochondrial aconitase and other enzymes associated with the citric acid cycle. 651 May 22

In Bacillus subtilis, conditions causing partial deprivation of guanine nucleotides initiated sporulation and caused the synthesis of citrate synthase, aconitase, and alpha-ketoglutarate dehydrogenase. Alpha-ketoglutarate dehydrogenase could also be induced by acetate, and the specific activity of this enzyme was elevated in mutants that had high intracellular acetyl coenzyme A concentrations because they lacked citrate synthase activity. After deprivation of guanine nucleotides, the intracellular concentration of acetyl coenzyme A also increased, which explained the induction of alpha-ketoglutarate dehydrogenase. Furthermore, the decreases in alpha-ketoglutarate and L-malate concentrations observed during this deprivation accounted for the observed increases in citrate synthase activity (which was repressed by alpha-ketoglutarate and malate) and aconitase activity (which was repressed by alpha-ketoglutarate).
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PMID:Induction of citric acid cycle enzymes during initiation of sporulation by guanine nucleotide deprivation. 678 18

The connection between the kinetics of citrate-isocitrate overproduction by Saccharomycopsis lipolytica in glucose media and the specific activities of the enzymes being related to overproduction has been investigated. The specific activities of citrate synthase, aconitate hydratase, NAD+-linked and NADP+-linked isocitrate dehydrogenase decline significantly after exhaustion of the nitrogen source, whereas the activity of the pyruvate carboxylase remains relatively constant and corresponds to changes of the production rate. The results are compared with those obtained by fermentations in n-alkane media and discussed in relation to mechanisms of overproduction.
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PMID:[Enzymatic study of citrate-isocitrate accumulation in yeast with glucose as the carbon source]. 686 52

The activity of enzymes of the citrate and glyoxylate cycles was comparatively assayed in the parent strain of Candida lipolytica producing citric and isocitric acids in a medium with hexadecane and in its two mutants one of which produced citrate and the other synthesized isocitrate. The enzyme activities were determined in the dynamics of the yeast growth: (a) in the exponential growth phase (no production of the acids); (b) in the lag phase (the beginning of the acid production); and (c) in the stationary phase (active production of the acids). All of the strains had a high activity of citrate synthase. The mutant producing citrate exhibited a high activity of isocitrate lyase and a low activity of aconitate hydratase, whereas the mutant producing isocitrate manifested a high activity of aconitate hydrase and a low activity of isocitrate dehydrogenase and isocitrate lyase. The data pertinent to a change in the enzyme activities due to the growth limitation with a nitrogen source and the production of the acids are considered for explaining the mechanism of overproduction of citric and isocitric acids from n-alkanes by yeast organisms.
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PMID:[Citrate and glyoxylate cycle enzyme activity in citric and isocitric acid synthesis by different strains of Candida lipolytica]. 707 Mar 6

Activities of citrate synthase, aconitase, NAD- and NADP-dependent isocitrate dehydrogenases were studied in mitochondria of heart and skeletal muscles of embryos and adult rabbits. Activity of these enzymes was some times lower in embryonal skeletal muscles as compared with the muscles of adult animals. Differences in activities of citrate synthase, aconitase and NADP-dependent isocitrate dehydrogenase were unsignificant in heart muscles of embryos and adult animals. Activity of NAD-dependent isocitrate dehydrogenase was distinctly higher in embryonal heart than in adult rabbits. The kinetic parameters enabled to conclude that in vitro regulation of NAD-dependent oxidation of isocitrate by substrate and activator ADP, characteristic for the enzyme from tissues of adult animals, was also found in embryos.
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PMID:[Enzymes of citrate and isocitrate conversion in the heart and skeletal muscle mitochondria of embryos and adult rabbits]. 742 88


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