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 purposes of the present study were to characterize the histochemical and enzymatic profiles of various hindlimb skeletal muscles, as well as to determine maximal O2 consumption (VO2max) and respiratory exchange ratios (R) during steady-state exercise in the obese Zucker rat. The changes that occurred in these parameters in response to a 6-wk training program were then assessed. Obese rats were randomly assigned to a sedentary or training group. Lean littermates served as a second control. Training consisted of treadmill running at 18 m/min up an 8% grade, 1.5 h/day, 5 day/wk for 6 wk. During week 6, VO2max and R during a steady-state run (74% max) were determined. After 2 days of inactivity, hindlimb muscles were excised, stained for fiber type and capillaries, and assayed for hexokinase, citrate synthase, cytochrome oxidase, and beta-hydroxyacetyl-CoA dehydrogenase. The obese sedentary rats demonstrated greater oxidative enzyme activities per gram of muscle tissue than their lean littermates, greater R values during submaximal exercise of the same relative intensity, and greater absolute VO2max values. Training resulted in a 20-56% increase in oxidative enzymes, a 10% increase in VO2max, and an increase in capillary density in the soleus and plantaris. There was no alteration in R values during exercise at 74% VO2max or in fiber type composition in response to exercise training. Results suggest that the muscle of the obese Zucker rat manifests a greater oxidative capacity than the muscle of its lean littermates. The apparent inability of the obese rat to increase its use of fat during submaximal exercise of the same relative intensity in response to training remains to be elucidated.
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PMID:Muscle morphological and biochemical adaptations to training in obese Zucker rats. 255 20

Experiments are presented which show that oxaloacetate and analogs thereof with (R)-malate substructure, on interaction with citrate synthase linked to synthase 8-anilinonaphthalene 1-sulfonate (ANS), induce identical conformational changes of a characteristic magnitude. A conformational change of lower magnitude is also produced on binding of CoASH or ATP to citrate synthase.ANS and is completed on addition of oxaloacetate. The significance of these ligand-dependent conformational changes is discussed.
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PMID:Ligand-induced conformational changes of citrate synthase studied with the fluorescent probe 8-anilinonaphthalene 1-sulfonate. 258 90

The rate of utilization of pyruvate (at various concentrations) was measured in lymphocytes prepared from rat mesenteric lymph nodes. The quantitative contribution of pyruvate to CO2, lactate, aspartate, alanine, citrate, acetate, acetyl-CoA and ketone bodies accounted for the pyruvate metabolized. Pyruvate utilization was depressed by increasing concentrations of pyruvate. The maximum catalytic activities and selected intracellular distributions of the following enzymes of pyruvate, citrate and acetyl-CoA metabolism were measured: citrate synthase, ATP-citrate lyase, lactate dehydrogenase, acetyl-CoA hydrolase, acetylcarnitine transferase, NAD+- and NADP+- isocitrate dehydrogenases, HMG-CoA lyase, HMG-CoA synthase, Pyruvate dehydrogenase, acetoacetyl-CoA thiolase, 3-oxoacid-CoA transferase, 3-hydroxybutyrate dehydrogenase and pyruvate carboxylase. Acetyl-CoA formed from pyruvate did not contribute to the respiratory energy metabolism of resting lymphocytes. Instead acetyl-CoA was converted to acetoacetate by reactions which may favour the pathway catalyzed by acetoacetyl-CoA thiolase and 3-oxoacid-CoA transferase. Acetate, acetyl- and palmitoyl-carnitine inhibited the decarboxylation of [1-14C] pyruvate. These observations may be connected with the suppression of pyruvate utilization by increased pyruvate substrate concentration. Only very small amounts of either pyruvate or acetate were incorporated into lipids in resting lymphocytes. The amounts incorporated were partitioned in approximately the same pattern into FFA, T.G., cholesterol and cholesterol esters. Taken together the data show that pyruvate metabolism is directed inter alia at the formation of acetoacetate which may serve as a lipid synthesis precursor. When pyruvate utilization and metabolism was enhanced by concanavalin A, then acetoacetate formation was not favoured and from this it is proposed that the acetyl units may then be directed into lipid synthesis and may also make a contribution to the energy metabolism of the activated lymphocyte.
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PMID:Pyruvate metabolism by lymphocytes: evidence for an additional ketogenic tissue. 261 47

Insulin action was assessed in thighs of five healthy young males who had one knee immobilized for 7 days by a splint. The splint was not worn in bed. Subjects also used crutches to prevent weight bearing of the immobilized leg. Immobilization decreased the activity of citrate synthase and 3-OH-acyl-CoA-dehydrogenase in the vastus lateralis muscle by 9 and 14%, respectively, and thigh volume by 5%. After 7 days of immobilization, a two-step euglycemic hyperinsulinemic clamp procedure combined with arterial and bilateral femoral venous catheterization was performed. Insulin action on glucose uptake and tyrosine release of the thighs at mean plasma insulin concentrations of 67 (clamp step I) and 447 microU/ml (clamp step II) was decreased by immobilization, whereas immobilization did not affect insulin action on thigh exchange of free fatty acids, glycerol, O2, or potassium. Before and during the clamp step I, lactate release was significantly higher in the immobilized than in the control thigh. Seven days of one-legged immobilization causes local decreased insulin action on thigh glucose uptake and net protein degradation.
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PMID:Insulin action in human thighs after one-legged immobilization. 266 54

In-vitro translation of anglerfish islet mRNA revealed three glucagon precursors (preproglucagons): one with Mr 16,000 and two with Mr 14,000. The two Mr 14,000 precursors were well separated upon isoelectric focusing gels (pI values of 7.2 and 7.3), but had identical peptide maps. Translation of hybrid-selected Mr 14,000 preproglucagon mRNA in the presence of microsomal vesicles revealed that both precursors were processed to the same proglucagon. Northern blot analysis detected two mRNA species encoding Mr 14,000 precursor. A full-length Mr 14,000 preproglucagon cDNA was subcloned into a transcription vector, and coupled in-vitro transcription-translation was performed; surprisingly, both Mr 14,000 precursors were synthesized. To test whether acetylation of the free amino terminus generated the more acidic precursor, acetylase activity was partially inactivated with the inhibitor S-acetonyl-CoA, and acetyl-CoA was depleted by addition of oxaloacetate and citrate synthetase. Under these conditions, the level of the most basic preproglucagon was greatly enhanced, but when exogenous acetyl-CoA was added, the acidic form predominated. We conclude that acetylation generates the acidic precursor, and we discuss the implications of our findings for the biogenesis of other peptide hormones.
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PMID:In-vitro biosynthesis of multiple preproglucagons results from acetylation of the primary translation products. 267 84

The purpose of this investigation was to determine how models of weightlessness, hindlimb suspension (HS), and hindlimb immobilization (HI) affect the metabolic enzyme profile in the slow oxidative (SO), fast oxidative glycolytic (FOG), and fast glycolytic (FG) fibers of rat hindlimb. After 1, 2, or 4 wk of HS or HI, single fibers were isolated from freeze-dried soleus and gastrocnemius muscles; a small section of each fiber was run on sodium dodecyl sulfate-polyacrylamide gel electrophoresis gels to identify fiber type, and the remaining piece was assayed for either lactate dehydrogenase (LDH) and citrate synthase (CS) or phosphofructokinase (PFK) and beta-hydroxyacyl-CoA dehydrogenase (beta-OH-acyl-CoA). Two weeks of HS induced an almost twofold increase in the activity of CS (2.13 +/- 0.13 vs. 3.60 +/- 0.26 mol.kg dry wt-1.h-1) in the SO fiber of the soleus, and the activity stayed high at 4 wk. Although the FOG fiber had significantly higher CS activity (3.85 +/- 0.29) than either the SO or FG (1.59 +/- 0.16 mol.kg dry wt-1.h-1) fiber, neither fast fiber type was altered by HS. The glycolytic enzymes LDH and PFK were both elevated in the SO fiber after HS. The increase in LDH occurred by 1 wk (14.80 +/- 1.51 vs. 8.83 +/- 0.78), whereas the activity of PFK was not significantly changed until 4 wk (1.16 +/- 0.13 vs. 0.68 +/- 0.05 mol.kg dry wt-1.h-1). The control FG fiber had the highest LDH (44.30 +/- 2.29) and PFK (2.40 +/- 0.16) activities, followed by the FOG fiber (LDH, 34.10 +/- 2.83; PFK, 1.62 +/- 0.17 mol.kg dry wt-1.h-1); however, the activities of these glycolytic enzymes in the fast fiber types were unaltered by HS. The activity of beta-OH-acyl-CoA was not affected by HS in either the slow or fast fiber types. HI showed qualitatively similar changes to those observed with HS; however, the enzyme shifts developed with a slower time course. In conclusion, both HS and HI shifted the SO fiber enzyme pattern toward that of the control FOG fiber; however, a complete conversion from the SO to FOG fiber did not occur within the 4-wk treatment period.
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PMID:Single muscle fiber enzyme shifts with hindlimb suspension and immobilization. 271 97

Citrate synthase catalyzes the slow condensation of acetyldithio-CoA [Ac(= S)CoA] with oxalacetate to form thiocitrate [Wlassics, I.D., Stille, C., & Anderson, V.E. (1988) Biochim. Biophys. Acta 952, 269]. During the transient approach to steady state an observable amount of the dithioester absorbance disappears. The amplitude of the decrease in absorbance corresponds to 0.32, 0.03, and 0.02 enzyme equiv at pH 8.3, 7.5, and 6.6, respectively. The difference spectra from before and after the transient exhibit the dithioester lambda max at 306 nm. Acid quenching of a stiochiometric reaction between Ac(= S)CoA and citrate synthase following the transient quantitatively regenerates Ac(= S)CoA, indicating carbon-carbon bond formation had not yet occurred. The apparent first-order rate constant of the transient is independent of Ac(= S)CoA concentration and increases with decreasing pH, being 0.007, 0.016, and 0.04 s-1 at pH 8.3, 7.5, and 6.6, respectively. 2-Fluoroacetyldithio-CoA is a better inhibitor of citrate synthase, Ki = 300 nM, and substrate, Vmax = 2 X 10(-3) s-1, than Ac(= S)CoA. 1H NMR experiments indicate that citrate synthase catalyzes the exchange of the alpha-hydrogens of Ac(= S)CoA with turnover numbers of 0.13 and 0.54 s-1 at pD 7.9 and 7.2, respectively. Analysis of the proton and deuterium decoupled 13C NMR spectra of [2-13C]Ac(= S)CoA that has exchanged 37% of the alpha-hydrogens in the presence of citrate synthase indicates that the relative proportions of CH3, CH2D, CHD2, and CD3 were 0.29, 0.39, 0.25, and 0.07, respectively. This statistical distribution indicates each exchange event is independent. The data indicate that citrate synthase stabilizes the ionized form of Ac(= S)CoA by 5 kcal/mol relative to the un-ionized form, that the ionized dithioester is on the reaction pathway, and that below pH 8.3 the slow carbon-carbon bond forming reaction is responsible for the 10(6) decrease in Vmax caused by substituting sulfur for oxygen in the thioester carbonyl.
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PMID:Citrate synthase stabilizes the enethiolate of acetyldithio coenzyme A. 271 24

Arguments are presented which indicate that the low steady-state rates of citrate production governing the catalytic interaction of citrate synthase from pig heart with citryl-CoA reflect the formation of a non-productive enzyme.citryl-CoA complex. The kinetic predictions of such an extended reaction mechanism are examined and are shown to account in satisfactory detail for the complex multiphasic rate behaviour exhibited by the enzyme under a variety of conditions in reactions involving citryl-CoA as a substrate.
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PMID:Mechanism of interaction of citrate synthase with citryl-CoA. 273 46

A rapid and simple spectrophotometric method was developed to measure the activity of the condensing enzyme component of the microsomal fatty acid chain elongation system. The intermediate product of the condensation reaction is the beta-ketoacyl CoA which exists in two tautomeric forms, i.e., keto and enol. The addition of bovine serum albumin (BSA) to a cuvette cell containing a beta-ketoacyl CoA derivative resulted in the formation of a 303-nm absorbance peak, characteristic of enolate formation. The beta-ketoacyl CoAs with carbon chain length of 6 to 18 interacted with BSA to produce the 303-nm peak; acetoacetyl CoA was the only beta-keto compound tested which did not interact with BSA to produce the peak. Other compounds which were unaffected by BSA included CoA, free beta-keto acid, beta-hydroxyacyl CoA, acyl CoA, trans-2-enoyl CoA, and malonyl CoA. BSA could not be replaced by ovalbumin; furthermore, denatured (boiling) BSA could not induce the 303-nm peak. The specific activity of the condensing enzyme measured by the spectrophotometric method compares favorably with the activity obtained by the radioactive method. The apparent extinction coefficient (epsilon) for the absorbance peak generated by the beta-keto thioester varied from 5 to 30 mM-1 cm-1 depending on the beta-keto derivative. The spectrophotometric procedure can be used in the determination of the condensing enzyme activity in not only hepatic microsomes but also in kidney and brain microsomes both of which have significantly lower activity. The advantages of the novel method over the radioactive method are that (i) it does not involve the use of radioactive compounds, (ii) it is much less cumbersome and significantly less costly, and (iii) it is rapid and easy to perform.
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PMID:Spectrophotometric assay for the condensing enzyme activity of the microsomal fatty acid chain elongation system. 277 74

The activity of phosphofructokinase (PFK), citrate synthetase (CS), lactate dehydrogenase (LDH), 3-OH-CoA dehydrogenase (ACDH) and cytochrome-c-oxidase (cyt-ox) was measured in right atrial auricle and abdominal rectal muscle biopsies from 24 children, aged 3-12 years, with congenital heart malformations. Twelve children had cyanotic conditions (tetralogy of Fallot or truncus malformations) and 14 were noncyanotic (septal defects or vascular lesions). The cyt-ox activity was significantly higher in the cyanotic subgroup than in the noncyanotic (skeletal muscle: 55.71 +/- 10.4 vs 19.48 +/- 2.6 mmol/g protein/min, p less than 0.01; auricle: 93.1 +/- 11.8 vs 65.58 +/- 7.5, p less than 0.05). There were no significant differences between the activities of PFK, LDH, CS or ACDH in the cyanotic and noncyanotic groups. Within the normal range of hemoglobin and hematocrit, there was no correlation between these parameters and cyt-ox. On the other hand, above the normal range of hemoglobin and hematocrit a correlation coefficient of 0.89 (p less than 0.01) was observed which suggests the higher cyt-ox activity to be an adaptive phenomenon triggered by reduced availability of oxygen.
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PMID:Enzymatic activities in heart and skeletal muscle of children with cyanotic and noncyanotic congenital heart disease. 285 53


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