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 influence of tapering on the metabolic and performance parameters in endurance cyclists was investigated. Cyclists (n = 25) trained 5 days.week-1, 60 min.day-1, at 75-85% maximal oxygen consumption (VO2max) for 8 weeks and were then randomly assigned to a taper group: 4D (4 days; n = 7), 8D (8 days; n = 6), CON (control, 4 days rest; n = 6), NOTAPER (non-taper, continued training; n = 6). Muscle biopsy specimens taken before and after training and tapering were analysed for carnitine palmityltransferase (CPT), citrate synthase, beta-hydroxyacyl CoA dehydrogenase (HOAD), cytochrome oxidase (CYTOX), lactate dehydrogenase, glycogen and protein. Significant increases in VO2max (6%), a 60-min endurance cycle test (34.5%), oxidative enzymes (77-178%), glycogen (35%) and protein (34%) occurred following training. After the taper, HOAD and CPT decreased 25% (P less than 0.05) and 26% respectively, in the CON. Post-taper CYTOX values were different (P less than 0.05) for 4D and 8D compared with CON. Muscle glycogen levels were increased (P less than 0.05) after tapering in the 4D, 8D and CON, but decreased in NOTAPER. Similarly, power output at ventilation threshold was significantly increased in the 4D (27.4 W) and 8D (27 W) groups, but decreased (22 W) in the NOTAPER. These findings suggest that tapering elicited a physiological adaptation by altering oxidative enzymes and muscle glycogen levels. Such an adaptation may influence endurance cycling during a laboratory performance test.
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PMID:The effects of a reduced exercise duration taper programme on performance and muscle enzymes of endurance cyclists. 150 37

Addition of benzoate to the medium reservoir of glucose-limited chemostat cultures of Saccharomyces cerevisiae CBS 8066 growing at a dilution rate (D) of 0.10 h-1 resulted in a decrease in the biomass yield, and an increase in the specific oxygen uptake rate (qO2) from 2.5 to as high as 19.5 mmol g-1 h-1. Above a critical concentration, the presence of benzoate led to alcoholic fermentation and a reduction in qO2 to 13 mmol g-1 h-1. The stimulatory effect of benzoate on respiration was dependent on the dilution rate: at high dilution rates respiration was not enhanced by benzoate. Cells could only gradually adapt to growth in the presence of benzoate: a pulse of benzoate given directly to the culture resulted in wash-out. As the presence of benzoate in cultures growing at low dilution rates resulted in large changes in the catabolic glucose flux, it was of interest to study the effect of benzoate on the residual glucose concentration in the fermenter as well as on the level of some selected enzymes. At D = 0.10 h-1, the residual glucose concentration increased proportionally with increasing benzoate concentration. This suggests that modulation of the glucose flux mainly occurs via a change in the extracellular glucose concentration rather than by synthesis of an additional amount of carriers. Also various intracellular enzyme levels were not positively correlated with the rate of respiration. A notable exception was citrate synthase: its level increased with increasing respiration rate. Growth of S. cerevisiae in ethanol-limited cultures in the presence of benzoate also led to very high qO2 levels of 19-21 mmol g-1 h-1. During growth on glucose as well as on ethanol, the presence of benzoate coincided with an increase in the mitochondrial volume up to one quarter of the total cellular volume. Also with the Crabtree-negative yeasts Candida utilis, Kluyveromyces marxianus and Hansenula polymorpha, growth in the presence of benzoate resulted in an increase in qO2 and, at high concentrations of benzoate, in aerobic fermentation. In contrast to S. cerevisiae, the highest qO2 of these yeasts when growing at D = 0.10 h-1 in the presence of benzoate was equal to, or lower than the qO2 attainable at mu(max) without benzoate. Enzyme activities that were repressed by glucose in S. cerevisiae also declined in K. marxianus when the glucose flux was increased by the presence of benzoate.(ABSTRACT TRUNCATED AT 400 WORDS)
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PMID:Effect of benzoic acid on metabolic fluxes in yeasts: a continuous-culture study on the regulation of respiration and alcoholic fermentation. 152 84

5-Aminolevulinic acid (ALA), a heme precursor that accumulates in acute intermittent porphyria patients and lead-exposed individuals, has previously been shown to autoxidize with generation of reactive oxygen species and to cause in vitro oxidative damage to rat liver mitochondria. We now demonstrate that chronically ALA-treated rats (40 mg/kg body wt every 2 days for 15 days) exhibit decreased mitochondrial enzymatic activities (superoxide dismutase, citrate synthase) in liver and soleus (type I, red) and gastrocnemius (type IIb, white) muscle fibers. Previous adaptation of rats to endurance exercise, indicated by augmented (cytosolic) CuZn-superoxide dismutase (SOD) and (mitochondrial) Mn-SOD activities in several organs, does not protect the animals against liver and soleus mitochondrial damage promoted by intraperitoneal injections of ALA. This is suggested by loss of citrate synthase and Mn-SOD activities and elevation of serum lactate levels, concomitant to decreased glycogen content in soleus and the red portion of gastrocnemius (type IIa) fibers of both sedentary and swimming-trained ALA-treated rats. In parallel, the type IIb gastrocnemius fibers, which are known to obtain energy mainly by glycolysis, do not undergo these biochemical changes. Consistently, ALA-treated rats under swimming training reach fatigue significantly earlier than the control group. These results indicate that ALA may be an important prooxidant in vivo.
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PMID:5-aminolevulinic acid-induced alterations of oxidative metabolism in sedentary and exercise-trained rats. 153 18

Substrate and intermediate analogue inhibitors of enzymes were prepared in which the thioester oxygen of acyl-CoA substrates is replaced by hydrogen with formation of CoA-thioethers. Experiments performed with ATP citrate lyase and S-(3,4-dicarboxy-3-hydroxybutyl)-CoA are consistent with citryl-CoA but not with citryl-enzyme being the direct precursor of the products acetyl-CoA and oxaloacetate. Consistent with these results, a previously described isotopic exchange between acetyl-CoA and [3H]CoASH, indicating the formation of an acetyl-enzyme in the reaction pathway, could not be confirmed. Substrate analogue CoA-thioethers of malate synthase are inhibitors endowed with the affinity of the substrates. Acetyl carboxylase and fatty acid synthetase are not inhibited by the substrate analogue S-ethyl-CoA; S-carboxyethyl-CoA, which could substitute for malonyl-CoA, is likewise not inhibitory. An explanation is proposed. Previously suggested roles of S-carboxymethyl-CoA, an acetyl-CoA-related inhibitor of citrate synthase, are discussed in the light of new experimental data. S-Acetyl, S-propionyl and S-carboxymethyl derivatives of 1,N6-etheno-CoA loose the high affinity of their CoA-counterparts to citrate synthase, probably because the ethylene group prevents proper binding to the enzyme.
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PMID:Inhibitors of metabolic reactions. Scope and limitation of acyl-CoA-analogue CoA-thioethers. 167 5

Different point mutations of the mitochondrial genome, which all affect the ability of mitochondria to translate their own genes and lead to partial defects of mtDNA-dependent respiratory complexes, are related to distinct clinical mitochondrial disorders. A new maternally inherited disorder, characterised by a combination of adult-onset myopathy and cardiomyopathy, with no clinical involvement of the nervous system, was found in members of a single large pedigree. A heteroplasmic new mutation was identified in the mtDNA gene specifying tRNA(Leu)(UUR). This mutation segregated specifically with the disorder, and there were significant correlations between the proportion of the mtDNA that was of the mutant form and the activities (normalised for citrate synthase activity) of the two mtDNA-dependent respiratory enzymes (complex I, r = -0.71, p less than 0.005: complex IV r = -0.77, p less than 0.005) and the maximum oxygen consumption (r = -0.82, p less than 0.005), a physiological index of aerobic metabolism. These findings strongly suggest that the tRNA(Leu)(UUR) mutation is the genetic cause of this disorder, and that lesions of mtDNA should be considered in the differential diagnosis of the hereditary cardiomyopathies.
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PMID:Maternally inherited myopathy and cardiomyopathy: association with mutation in mitochondrial DNA tRNA(Leu)(UUR). 167 65

The maximum activities of some key enzymes of metabolism were studied in lungs of fed and 48-h-starved rats. The maximum activity of hexokinase in the lung is similar to that of other tissues of the body, but lower than that of phosphorylase and 6-phosphofructokinase. High activities of glucose-6-phosphate dehydrogenase and 6-phosphogluconate dehydrogenase were found in lung tissue, suggesting the importance of the pentose phosphate pathway in the lung. The activities of hexokinase and 6-phosphofructokinase were decreased whereas that of phosphorylase increased in response to starvation. Of the enzymes of the tricarboxylic acid cycle whose activities were measured, that of oxoglutarate dehydrogenase was the lowest, yet its activity (approximately 4.2 nmol/min per mg protein at 37 degrees C) was considerably greater than the flux through the cycle (0.46 nmol/min per mg protein at 37 degrees C; calculated from oxygen consumption by incubated lung slices). The activities of both oxoglutarate dehydrogenase and citrate synthase were decreased by starvation. The activities of 3-oxoacid CoA-transferase and acetoacetyl-CoA thiolase were low in lung tissue compared to those of other tissues (eg kidney, brain) and that of 3-hydroxybutyrate dehydrogenase was very low. The activity of carnitine palmitoyl transferase is higher in the lung, suggesting that fatty acids (and possibly acetoacetate) could provide acetyl-CoA as substrate for the tricarboxylic acid cycle. Very low rates of utilization of 3-hydroxybutyrate were observed during incubation of lung slices, but that of oleate was 1.2 nmol/h per mg of protein.(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:Metabolism of glucose, glutamine, long-chain fatty acids and ketone bodies by lungs of the rat. 176

The development of oxidative metabolism was studied from the late fetal to adult stages in mitochondria isolated from rat kidney. We used the oxygen consumption rate, as an index of inner membrane activity and citrate synthase and fumarase activities as an index of matrix activity and cytochrome c oxidase activity as an index of the number of mitochondria. Fumarase and citrate synthase activities displayed different developmental patterns, suggesting that these Krebs cycle enzymes did not mature synchronously. In fetal mitochondria, net oxygen consumption measured in the presence of succinate or glutamate as substrate, was low; it increased during the day after birth and reached adult level between days 10 and 15. During this period, the levels of citrate synthase and cytochrome c oxidase activity did not change significantly in the isolated mitochondrial fraction. However, in fetal and adult kidney homogenates, these levels increased four-fold, suggesting a corresponding increase in the number of mitochondria. Most of these increases occurred during the 15 days after birth. These results suggest that in rat kidney, mitochondrial maturation precedes the maturation of reabsorptive ion transport and does not limit its development.
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PMID:Mitochondrial activity of rat kidney during ontogeny. 196 37

The activity patterns of enzyme linked to energy transduction are measured as an estimate of the energy potential capacity of the brain during aging. Early investigations provided information on age-related modifications in the apparent activity of these enzymes in the brain as a whole without taking into account the anatomical, morphological, and functional heterogeneity of the discrete brain regions, the metabolic compartments, and their different time course of aging processes. These considerations prompted the investigators to focus their efforts on subcellular organelles, representative of metabolic compartments, isolated from selected brain regions. In the present study, to better elucidate the role of the synaptic compartment during aging, the maximum rate (Vmax) of enzymes involved in energy metabolic pathways is evaluated in synaptosomes isolated from the cerebral cortex of rats aged 4, 12, and 24 months. The potential catalytic activity of phosphofructokinase and citrate synthase is not affected by aging. In contrast, the Vmax of pyruvate dehydrogenase and particularly of cytochrome oxidase decreases in aged rats. A marked increase is found in the Vmax of glucose-6-phosphate dehydrogenase in 24-month-old rats and could support the availability of nicotinamide adenine dinucleotide phosphate (NADPH) for antiperoxidative processes. Pretreatments of the animals with certain drugs are performed in order to check the responsiveness of the tissue and the plasticity of enzyme proteins during aging. Papaverine (acting on macrocirculation) is ineffective, but raubasine (acting on microcirculation and metabolism) and almitrine (acting on oxygen availability) both interfere with the potential activity of some of the enzymes tested. Their influence differs with the age of the animal and are in agreement with their action on brain carbohydrate and phospholipid metabolism.
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PMID:Role of synaptosomal enzymatic alterations and drug treatment in brain aging. 196 31

Functional and metabolic responses of hypothyroid skeletal muscle were evaluated during steady-state isometric contraction conditions, using an isolated perfused rat hindlimb preparation. Treating rats with propylthiouracil (PTU) for 4-5 mo resulted in a 55% decrease (P less than 0.001) in citrate synthase activity in plantaris muscle and phenotypic remodeling of the plantaris, evident by a threefold increase in type I fiber area and a 13% decrease in type II fiber area. Perfusion of PTU (n = 9) and control (n = 9) rat hindlimbs of similar size, with similar inflow (approximately 10 ml/min) and oxygen content (approximately 20 g/100 ml), resulted in similar oxygen deliveries to the contracting muscles (PTU 11.4 +/- 0.58, control 9.54 +/- 0.75 mumol.min-1.g-1; P greater than 0.05). Ten-minute tetanic contraction (100 ms at 100 Hz) periods at 4, 8, 15, 30, and 45 tetani/min were elicited in consecutive ascending order. Oxygen consumption (VO2) was lower in the PTU group at all contraction frequencies (P less than 0.005), with a decrease in peak VO2 of 44% (PTU 3.01 +/- 0.29, control 5.35 +/- 0.42 mumol.min-1.g-1; P less than 0.001). Oxygen extraction by the PTU muscle was only approximately 25% of that delivered. Developed tension was initially less (15%; P less than 0.05) in the PTU group but declined in a similar manner, as a percent of initial, to that of the control group. The slightly lower absolute tension development of the PTU muscle could not account for the large reduction in VO2.(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:Functional and metabolic consequences of skeletal muscle remodeling in hypothyroidism. 199 31

The structures of four isomorphous crystals of ternary complexes of chicken heart citrate synthase with D- or L-malate and acetyl coenzyme A or carboxymethyl coenzyme A have been determined by X-ray crystallography and fully refined at 1.9-A resolution. The structures show that both L-malate and D-malate bind in a very similar way in the presence of acetylCoA and that the enzyme conformation is "closed". Hydrogen bond geometry is suggested to account for the difference in binding constants of the two stereoisomers. The structures suggest that steric hindrance can account for the observation that proton exchange of acetyl coenzyme A with solvent is catalyzed by citrate synthase in the presence of L-malate but not D-malate. The ternary complexes with malate reveal the mode of binding of the substrate acetylCoA in the ground state. The carbonyl oxygen of the acetyl group is hydrogen bonded to a water molecule and to histidine 274, allowing unambiguous identification of the orientation of this group. The structures support the hypothesis that carboxymethyl coenzyme A is a transition-state analogue for the enolization step of the reaction (Bayer et al., 1981) and additionally support proposed mechanisms for the condensation reaction (Karpusas et al., 1990; Alter et al., 1990).
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PMID:1.9-A structures of ternary complexes of citrate synthase with D- and L-malate: mechanistic implications. 204 40


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