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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)

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

The enzyme complement of two different mitochondrial preparations from adult rat brain has been studied. One population of mitochondria (synaptic) is prepared by the lysis of synaptosomes, the other (non-synaptic or free) by separation from homogenates. These populations have been prepared from distinct regions of the brain: cortex, striatum, and pons and medulla oblongata. The following enzymes have been measured: pyruvate dehydrogenase (EC 1.2.4.1), citrate synthase (EC 4.1.3.7), NAD-linked isocitrate dehydrogenase (EC 1.1.1.41), NADP-linked isocitrate dehydrogenase (EC 1.1.1.42), fumarase (EC 4.2.1.2), NAD-linked malate dehydrogenase (EC 1.1.1.37), D-3-hydroxybutyrate dehydrogenase (EC 1.1.1.30), and mitochondrially bound hexokinase (EC 2.7.1.1) and creatine kinase (EC 2.7.3.2). The nonsynaptic (free) mitochondria show higher enzyme specific activities in the regions studied than the corresponding values recorded for the synaptic mitochondria. The significance of these observations is discussed in the light of the different metabolic activities of the two populations of mitochondria and the compartmentation of the metabolic activities of the brain.
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PMID:The activities of some energy-metabolising enzymes in nonsynaptic (free) and synaptic mitochondria derived from selected brain regions. 670 35

The development of several key enzymes of pyruvate and 3-hydroxybutyrate metabolism and of the tricarboxylic acid cycle was studied in six regions (cerebellum, medulla oblongata and pons, hypothalamus, striatum, mid-brain and cortex) of the neonatal, suckling and adult rat brain (2 days before birth to 60 days after birth). The enzymes whose developmental patterns were studied were: pyruvate dehydrogenase (EC 1.2.4.1), 3-hydroxybutyrate dehydrogenase (EC 1.1.1.30), citrate synthase (EC 4.1.3.7), NAD-linked isocitrate dehydrogenase (EC 1.1.1.41) and fumarase (EC 4.2.1.2). Citrate synthase, isocitrate dehydrogenase and pyruvate dehydrogenase develop as a cluster in each region, although the pyruvate dehydrogenase appears to lag slightly behind the others. As with the glycolytic-enzyme cluster [Leong & Clark (1984) Biochem. J. 218, 131-138] the timing of the development of the activity of this group of enzymes varies from region to region; 50% of the adult activity developed first in the medulla oblongata, followed by the hypothalamus, striatum and mid-brain, and then in the cortex and cerebellum respectively. The 3-hydroxybutyrate dehydrogenase activity also develops earlier in the medulla oblongata than in the other regions. The results are discussed with respect to the neurophylogenetic development of the brain regions studied and the importance of the development of the enzymes of aerobic glycolysis in relationship to the development of neurological maturation.
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PMID:Regional enzyme development in rat brain. Enzymes of energy metabolism. 671 10

meso-Tartrate inhibited the growth of non-meso-tartrate-utilizing strains of Salmonella typhimurium in peptone water media and mineral salts media with some, but not all, carbon sources. C-R intermediates of the tricarboxylic acid cycle or compounds readily converted to them and substrates metabolized independently of the C-6 part of the cycle spared bacteria from the inhibitory effects of meso-tartrate when added to cultures along with meso-tartrate. Experiments with cell-free extracts of non-meso-tartrate-utilizing strains from batch and continuous cultures showed that meso-tartrate was a competitive inhibitor of isocitrate dehydrogenase and isocitrate lyase activities and also inhibited citrate synthase and malate synthase activities. The synthesis of these enzymes was not inhibited by meso-tartrate. The isocitrate enzymes of meso-tartrate-utilizing strains of S. typhimurium were similarly inhibited by meso-tartrate, but inhibition of the growth of meso-tartrate-utilizing strains was demonstrable only in uninduced cultures in which the intracellular concentrations of meso-tartrate were high.
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PMID:Physiological basis for meso-tartrate sensitivity in some strains of Salmonella typhimurium. 699 76

The activity of 22 enzymes of energy metabolism was determined in m. vastus lateralis quadricipitis of 14 adolescents aged 13-15 years (7 girls) and 14 adults aged 22 to 42 years (7 female subjects). The measurements were performed kinetically, at 37 degrees C, using optimal or near-to-optimal procedures. With the exception of one enzyme, enolase, no differences between sexes were observed in the two age groups. Glycolytic enzymes, including fructose-6-phosphate kinase, showed no significant differences in their activity in adults as compared to adolescents. The activity of enolase was lower in females of both age groups, but no difference due to age was found in this respect. Of the oxidative enzymes studied, only citrate synthase showed no significant difference in adults vs adolescents, whereas the activities of lipoamide dehydrogenase (+ 40%), NADP-isocitrate dehydrogenase (+ 44%), fumarase (+ 24.5%), total malate dehydrogenase (+ 42.2%) and NADH-dehydrogenase (+ 39%) were all significantly higher in the latter group. Aspartate aminotransferase was also 44% higher in adolescents. The possible physiological importance of these observations is discussed with regard to the functional capacity of the skeletal muscle. The hypothesis was considered that adolescents of this age may have a glycolytic capacity comparable to adults, but that they may oxidize pyruvate at a rate higher than adults.
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PMID:Enzyme activities in skeletal muscle of 13-15 years old adolescents. 705 78

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

1. The role of pyruvate carboxylation in the net synthesis of tricarboxylic acid-cycle intermediates during acetate metabolism was studied in isolated rat hearts perfused with [1-14C]pyruvate. 2. The incorporation of the 14C label from [1-14C]pyruvate into the tricarboxylic acid-cycle intermediates points to a carbon input from pyruvate via enzymes in addition to pyruvate dehydrogenase and citrate synthase. 3. On addition of acetate, the specific radioactivity of citrate showed an initial maximum at 2 min, with a subsequent decline in labelling. The C-6 of citrate (which is removed in the isocitrate dehydrogenase reaction) and the remainder of the molecule showed differential labelling kinetics, the specific radioactivity of C-6 declining more rapidly. Since this carbon is lost in the isocitrate dehydrogenase reaction, the results are consistent with a rapid inactivation of pyruvate dehydrogenase after the addition of acetate, which was confirmed by measuring the 14CO2 production from [1-14C]pyruvate. 4. The results can be interpreted to show that carboxylation of pyruvate to the C4 compounds of the tricarboxylic acid cycle occurs under conditions necessitating anaplerosis in rat myocardium, although the results do not identify the enzyme involved. 5. The specific radioactivity of tissue lactate was too low to allow it to be used as an indicator of the specific radioactivity of the intracellular pyruvate pool. The specific radioactivity of alanine was three times that of lactate. When the hearts were perfused with [1-14C]lactate, the specific radioactivity of alanine was 70% of that of pyruvate. The results suggest that a subcompartmentation of lactate and pyruvate occurs in the cytosol.
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PMID:Pyruvate carboxylation as an anaplerotic mechanism in the isolated perfused rat heart. 708 18

The activities of enzymes of the tricarboxylic acid cycle were measured in order to compare the respiratory capacity in different parts of the nephron of the rat. Oxoglutarate dehydrogenase, citrate synthase and isocitrate dehydrogenase were assayed in single nephron segments dissected out of freeze-dried cryostat sections. The activities of the three enzymes per unit weight are higher in the distal segments (thick ascending limb and distal convoluted tubule) than in the proximal tubule. The distal vs. proximal ratios of activities are about 1.5, 2.5 and 2 for oxoglutarate dehydrogenase, citrate synthase and isocitrate dehydrogenase, respectively. Oxoglutarate dehydrogenase shows the lowest activities along the whole nephron and appears to catalyze the rate-limiting step of the tricarboxylic acid cycle. The possibility to estimate the respiratory capacity in the different segments of the nephron on the basis of the activity of oxoglutarate dehydrogenase is discussed. The capacity calculated for the proximal tubule (between 44 and 66 mumol O X min-1 X g-1, depending on the substrate) is in agreement with direct measurements of oxygen consumption as well as with calculations made on the basis of morphometrical data.
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PMID:Activities of enzymes of the tricarboxylic acid cycle in segments of the rat nephron. 715 97

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

Rhodopseudomonas capsulata can grow in a number of alternative modes, including (i) photosynthetic, defined here as anaerobic growth with light as the energy source, and (ii) heterotrophic, referring to aerobic heterotrophic growth in darkness. The functions of citric acid cycle sequences in these growth modes were investigated using wild-type and appropriate mutant strains. Results of growth tests and O(2) utilization experiments showed that in the heterotrophic mode, energy conversion is dependent on operation of the classical citric acid cycle. Alpha-ketoglutarate dehydrogenase (KGD) activity in wild-type strain B10 is substantially higher in cells grown heterotrophically than in cells grown photosynthetically. Molecular oxygen, even at low concentration, appears to be important in regulation of KGD synthesis and, thus, in expression of citric acid cycle activity. Extracts of (photosynthetically grown) mutant strain KGD11 lack demonstrable KGD activity, and in contrast to the wild type, KGD11 is unable to grow heterotrophically on succinate, malate, or pyruvate owing to failure of the energy conversion function of the citric acid cycle. KGD11, however, grows well photosynthetically on malate or on CO(2) + H(2). The KGD activity level required to support the bioenergetic function of the citric acid cycle is evidently much higher than that necessary to satisfy biosynthetic demands; thus, a very low rate of succinyl-coenzyme A formation (needed for biosynthesis) in the mutant would suffice for growth under photosynthetic conditions. In wild-type R. capsulata, the alpha-ketoglutarate required for glutamate synthesis is ordinarily generated via citric acid cycle reactions, which include the conversions catalyzed by citrate synthase and isocitrate dehydrogenase. Mutants blocked in the former or both of these enzymes can grow photosynthetically if provided with an exogenous source of alpha-ketoglutarate or glutamate, but grow very poorly (if at all) as heterotrophs since the energy supply under these conditions depends on operation of the complete citric acid cycle.
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PMID:Biosynthetic and bioenergetic functions of citric acid cycle reactions in Rhodopseudomonas capsulata. 729 78


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