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)

The regional enzyme activities of glucose metabolism in the rat brain were investigated. Hexokinase (EC 2.7.1.1) and pyruvate dehydrogenase (EC 1.2.4.1), key enzymes for glucose metabolism, showed no changes in activity in all the regions studied of the aging brain as compared with the adult brain. However, the activity of D-3-hydroxybutyrate dehydrogenase (EC 1.1.1.30) is low throughout the adult brain and, in contrast with hexokinase and pyruvate dehydrogenase, its activity decreases significantly during aging. Other enzymes that showed significant decreases during aging are aldolase (EC 4.1.2.13), lactate dehydrogenase (EC 1.1.1.27), citrate synthase (EC 4.1.3.7), and NAD+-linked isocitrate dehydrogenase (EC 1.1.1.41). The catabolic enzyme in cholinergic metabolism, acetylcholinesterase (EC 3.1.1.7), selected as an example of a non-energy-metabolising enzyme, also showed significant decreases in all regions of the brain in aging, although its highest activity remained in the striatum. These results are discussed with respect to the energy metabolism in various brain regions and their status with aging.
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PMID:Energy-metabolizing enzymes in brain regions of adult and aging rats. 646 Aug 51

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

Kinetic studies of the individual reaction of pig heart pyruvate dehydrogenase complex (pyruvate dehydrogenase (pyruvate:lipoamide oxidoreductase (decarboxylating and acceptor-acetylating), EC 1.2.4.1); dihydrolipoamide reductase(NAD+) (NADH:lipoamide oxidoreductase, EC 1.6.4.3); dihydrolipoamide acetyltransferase (acetyl-CoA:dihydrolipoamide S-acetyltransferase, EC 2.3.1.12)), citrate synthase (citrate oxaloacetate-lyase (pro-3S-CH2COO- leads to acetyl-CoA), EC 4.1.3.7) and the pyruvate dehydrogenase complex-citrate synthase coupled system show that the KmCoA value of pyruvate dehydrogenase complex and KmCoASAc value of citrate synthase decrease in the coupled system when compared to those in the individual enzyme reactions. The explanation for this interaction may be an association between the two enzymes. When it was centrifuged with 150 000 x g for 140 min, 30% of the citrate synthase sedimented in the presence of the pyruvate dehydrogenase complex, while no sedimentation was observed in the absence of the pyruvate dehydrogenase complex. Sedimentation of cytoplasmic malate dehydrogenase, phosphotransacetylase, hemoglobin and Blue albumin were negligible under the same condition. In gel chromatography experiments a significant peak of citrate synthase activity co-migrated with the pyruvate dehydrogenase complex peak. This observation also suggests the possible association of two enzymes.
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PMID:Interaction between the pyruvate dehydrogenase complex and citrate synthase. 721 36

The developmental and senescent patterns of a number of heart enzyme activities linked to energy metabolism have been studied in rats aged between 4 days and 21 months. A morphometric study of mitochondrial volume fractions and numbers has been also carried out. Developmental changes result in a rise of most mitochondrial enzymes (NADP+-isocitrate dehydrogenase, malic enzyme, succinate dehydrogenase, citrate synthase) and mitochondrial volume fractions. Exceptions are NAD+-isocitrate dehydrogenase, which declines from 4 days onwards, and NAD+-malate dehydrogenase, which declines and then rises over the same period. Senescent changes follow two different trends. While pyruvate kinase and those mitochondrial enzymes lying between citrate formation and isocitrate oxidation (citrate synthase, NADP+-and NAD+-isocitrate dehydrogenases) decline to some degree, mitochondrial succinate dehydrogenase and NAD+-malate dehydrogenase activities increase over the same period. This could point towards a partial impairment of Krebs cycle function, and a reduced energy-producing capacity in the aged rat heart.
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PMID:Comparison between developmental and senescent changes in enzyme activities linked to energy metabolism in rat heart. 726 74

We investigated how NADH generated during peroxisomal beta-oxidation is reoxidized to NAD+ and how the end product of beta-oxidation, acetyl-CoA, is transported from peroxisomes to mitochondria in Saccharomyces cerevisiae. Disruption of the peroxisomal malate dehydrogenase 3 gene (MDH3) resulted in impaired beta-oxidation capacity as measured in intact cells, whereas beta-oxidation was perfectly normal in cell lysates. In addition, mdh3-disrupted cells were unable to grow on oleate whereas growth on other non-fermentable carbon sources was normal, suggesting that MDH3 is involved in the reoxidation of NADH generated during fatty acid beta-oxidation rather than functioning as part of the glyoxylate cycle. To study the transport of acetyl units from peroxisomes, we disrupted the peroxisomal citrate synthase gene (CIT2). The lack of phenotype of the cit2 mutant indicated the presence of an alternative pathway for transport of acetyl units, formed by the carnitine acetyltransferase protein (YCAT). Disruption of both the CIT2 and YCAT gene blocked the beta-oxidation in intact cells, but not in lysates. Our data strongly suggest that the peroxisomal membrane is impermeable to NAD(H) and acetyl-CoA in vivo, and predict the existence of metabolite carriers in the peroxisomal membrane to shuttle metabolites from peroxisomes to cytoplasm and vice versa.
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PMID:The membrane of peroxisomes in Saccharomyces cerevisiae is impermeable to NAD(H) and acetyl-CoA under in vivo conditions. 762 49

We isolated and characterized mutants defective in nuo, encoding NADH dehydrogenase I, the multisubunit complex homologous to eucaryotic mitochondrial complex I. By Southern hybridization and/or sequence analysis, we characterized three distinct mutations: a polar insertion designated nuoG::Tn10-1, a nonpolar insertion designated nuoF::Km-1, and a large deletion designated delta(nuoFGHIJKL)-1. Cells carrying any of these three mutations exhibited identical phenotypes. Each mutant exhibited reduced NADH oxidase activity, grew poorly on minimal salts medium containing acetate as the sole carbon source, and failed to produce the inner, L-aspartate chemotactic band on tryptone swarm plates. During exponential growth in tryptone broth, nuo mutants grew as rapidly as wild-type cells and excreted similar amounts of acetate into the medium. As they began the transition to stationary phase, in contrast to wild-type cells, the mutant cells abruptly slowed their growth and continued to excrete acetate. The growth defect was entirely suppressed by L-serine or D-pyruvate, partially suppressed by alpha-ketoglutarate or acetate, and not suppressed by L-aspartate or L-glutamate. We extended these studies, analyzing the sequential consumption of amino acids by both wild-type and nuo mutant cells growing in tryptone broth. During the lag and exponential phases, both wild-type and mutant cells consumed, in order, L-serine and L-aspartate. As they began the transition to stationary phase, both cell types consumed L-tryptophan. Whereas wild-type cells then consumed L-glutamate, glycine, L-threonine, and L-alanine, mutant cells utilized these amino acids poorly. We propose that cells defective for NADH dehydrogenase I exhibit all these phenotypes, because large NADH/NAD+ ratios inhibit certain tricarboxylic acid cycle enzymes, e.g., citrate synthase and malate dehydrogenase.
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PMID:Mutations in NADH:ubiquinone oxidoreductase of Escherichia coli affect growth on mixed amino acids. 815 82

The activities of enzymes related to energy metabolism in the gastrocnemius and soleus muscles in young-adult (4 months), mature (12 months) and senescent (24 months) rats were compared after 72 h of continuous exposure to normobaric hypoxia or normoxia after alpha-adrenergic antagonist nicergoline or saline solution had been given intraperitoneally for 30 consecutive days. The maximum rates (Vmax) of the following enzyme activities in the crude extract and/or the mitochondrial fraction of each muscle specimen were evaluated: (1) for the anaerobic glycolytic pathway: hexokinase, phosphofructokinase, pyruvate kinase and lactate dehydrogenase; (2) for the tricarboxylic acid cycle; citrate synthase and malate dehydrogenase; (3) for the electron transfer chain; cytochrome oxidase; and (4) for the NAD+/NADH redox state: total NADH cytochrome c reductase. The significant differences between the enzyme activities at different ages or under different experimental conditions in the two tissue preparations of the two muscles were determined by ANOVA. MCA and ETA were used to evaluate the net effects of the experimental conditions. Ageing did not seem to affect the soleus and gastrocnemius muscles in the same way. Changes were seen only in the glycolytic pathway enzymes in the crude extract from the gastrocnemius muscle. In the soleus muscle changes in enzyme activities as a function of ageing were also found in the mitochondrial fraction. We also found that hypoxia caused greater changes in 12-month-old rats than in those of other ages (especially in the enzyme activities of the gastrocnemius muscle). Finally out data show that only in certain cases was the pharmacological treatment able to modify the influence of hypoxic conditions on the levels of enzyme activities, regardless of the age of animals.
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PMID:Effects of hypoxia on enzyme activities in skeletal muscle of rats of different ages. An attempt at pharmacological treatment. 873 89

In work previously reported (J. A. Gutierrez, P. J. Crowley, D. P. Brown, J. D. Hillman, P. Youngman, and A. S. Bleiweis, J. Bacteriol. 178:4166-4175, 1996), a Tn917 transposon-generated mutant of Streptococcus mutans JH1005 unable to synthesize glutamate anaerobically was isolated and the insertion point of the transposon was determined to be in the icd gene encoding isocitrate dehydrogenase (ICDH). The intact icd gene of S. mutans has now been isolated from an S. mutans genomic plasmid library by complementation of an icd mutation in Escherichia coli host strain EB106. Genetic analysis of the complementing plasmid pJG400 revealed an open reading frame (ORF) of 1,182 nucleotides which encoded an enzyme of 393 amino acids with a predicted molecular mass of 43 kDa. The nucleotide sequence contained regions of high (60 to 72%) homology with icd genes from three other bacterial species. Immediately 5' of the icd gene, we discovered an ORF of 1,119 nucleotides in length, designated citZ, encoding a homolog of known citrate synthase genes from other bacteria. This ORF encoded a predicted protein of 372 amino acids with a molecular mass of 43 kDa. Furthermore, plasmid pJG400 was also able to complement a citrate synthase (gltA) mutation of E. coli W620. The enzyme activities of both ICDH, found to be NAD+ dependent, and citrate synthase were measured in cell extracts of wild-type S. mutans and E. coli mutants harboring plasmid pJG400. The region 5' from the citZ gene also revealed a partial ORF encoding 264 carboxy-terminal amino acids of a putative aconitase gene. The genetic and biochemical evidence indicates that S. mutans possesses the enzymes required to convert acetyl coenzyme A and oxalacetate to alpha-ketoglutarate, which is necessary for the synthesis of glutamic acid. Indeed, S. mutans JH1005 was shown to assimilate ammonia as a sole source of nitrogen in minimal medium devoid of organic nitrogen sources.
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PMID:Role of the citrate pathway in glutamate biosynthesis by Streptococcus mutans. 900 16

A substrate cycle between citric acid cycle (CAC) intermediates isocitrate and 2-oxoglutarate, involving NAD+- and NADP+-linked isocitrate dehydrogenase (NAD-IDH and NADP-IDH, respectively) and mitochondrial transhydrogenase (H+-Thase), has recently been proposed. This cycle has been hypothesized to enhance mitochondrial respiratory control by increasing the sensitivity of NAD-IDH to its modulators and allowing for enhanced increases in flux through this step of the CAC during periods of increased ATP demand. The activities of the enzymes comprising the substrate cycle: NAD-IDH, forward and reverse NADP-IDH, and forward and reverse H+-Thase, along with the activity of a marker of mitochondrial content, citrate synthase (CS) were measured in mitochondria isolated from rabbit Type I and Type IIb muscles and in whole muscle homogenates, representing the various fiber types, from rats. In isolated rabbit muscle mitochondria, NAD-IDH had significantly higher (1.6 x ) activity in white muscle while forward NADP-IDH, forward and reverse H+-Thase, and CS all had significantly higher (1.2-1.6 x ) activities in red muscle. There was no difference in reverse NADP-IDH between fiber types. Similarly, in rat whole muscle enzyme activities normalized to CS, NAD-IDH had significantly higher activity in fast-twitch glycolytic (FG) fibers, while forward NADP-IDH and forward H+-Thase had significantly higher activities in slow-twitch oxidative (SO) fibers. These results suggest that differences in the activities of the substrate cycle enzymes between skeletal muscle fiber types could contribute to differences in respiratory control due to differential cycling rates and/or loci of control.
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PMID:Fiber-type-related differences in the enzymes of a proposed substrate cycle. 951 25

The eight enzymes of the tricarboxylic acid (TCA) cycle are encoded by at least 15 different nuclear genes in Saccharomyces cerevisiae. We have constructed a set of yeast strains defective in these genes as part of a comprehensive analysis of the interactions among the TCA cycle proteins. The 15 major TCA cycle genes can be sorted into five phenotypic categories on the basis of their growth on nonfermentable carbon sources. We have previously reported a novel phenotype associated with mutants defective in the IDH2 gene encoding the Idh2p subunit of the NAD+-dependent isocitrate dehydrogenase (NAD-IDH). Null and nonsense idh2 mutants grow poorly on glycerol, but growth can be enhanced by extragenic mutations, termed glycerol suppressors, in the CIT1 gene encoding the TCA cycle citrate synthase and in other genes of oxidative metabolism. The TCA cycle mutant collection was utilized to search for other genes that can suppress idh2 mutants and to identify TCA cycle genes that display a similar suppressible growth phenotype on glycerol. Mutations in 7 TCA cycle genes were capable of functioning as suppressors for growth of idh2 mutants on glycerol. The only other TCA cycle gene to display the glycerol-suppressor-accumulation phenotype was IDH1, which encodes the companion Idh1p subunit of NAD-IDH. These results provide genetic evidence that NAD-IDH plays a unique role in TCA cycle function.
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PMID:Genetic and biochemical interactions involving tricarboxylic acid cycle (TCA) function using a collection of mutants defective in all TCA cycle genes. 1022 50


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