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 anaplerotic hypothesis for insulin release postulates that an increased generation of malonyl-CoA, acyl residues and diacylglycerol in nutrient-stimulated pancreatic islets may couple the catabolism of nutrient secretagogues to more distal events in the secretory sequence. In the light of this hypothesis, pyruvate carboxylase activity was measured in rat pancreatic islets using two distinct radioisotopic procedures. The first procedure is based on the conversion of oxalacetate generated from pyruvate to 14C-labelled citrate in the presence of [1-14C]acetyl-CoA and citrate synthase. The second technique involves the conversion of 14C-labelled oxalacetate generated from [1-14C]pyruvate to radioactive aspartate in the presence of L-glutamate and glutamate-oxalacetate transaminase. Pyruvate carboxylase activity amounted to 10 pmol/min per islet, was restricted to mitochondria, displayed a Km for pyruvate close to 0.4 mM, and demonstrated dependency towards ATP (apparent Ka close to 0.1 mM), Mg2+ and acetyl-CoA. It is proposed that pyruvate carboxylase activity accounts for the generation of 14C-labelled amino acids other than alanine in islets exposed to D-[3,4-14C]glucose and participates to the pyruvate/citrate shuttle for the transport of acetyl-CoA out of the mitochondria in nutrient-stimulated islets.
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PMID:Hexose metabolism in pancreatic islets: pyruvate carboxylase activity. 176 3

The effect of exercise intensity on oral glucose tolerance and hindlimb glucose uptake and transport was studied in 26 female obese Zucker rats after a treadmill training program. The rats were randomly assigned to either a low-intensity (LI) or high-intensity (HI) exercise group, with equal work being performed by the two groups. A third group of rats served as sedentary controls (SED). The trained rats demonstrated a significant improvement in oral glucose tolerance while maintaining significantly lower plasma insulin concentrations when compared with the SED rats. However, no significant differences in plasma glucose or insulin concentrations were observed between the LI and HI exercise-trained groups. During hindlimb perfusion (500 microU/ml insulin, 8 mM glucose), the rate of muscle glucose uptake for the HI rats (13.5 +/- 0.8 mumol.h-1.g-1) was significantly faster than that of the LI rats (11.4 +/- 0.8 mumol.h-1.g-1), which was significantly faster than that of the SED rats (8.3 +/- 0.6 mumol.h-1.g-1). The rates of 3-O-methyl-D-glucose (3-MG) transport were substantially greater in the fast-twitch red fibers of the HI (10.11 +/- 0.49 mumol.h-1.g-1) and LI (9.08 +/- 0.46 mumol.h-1.g-1) rats when compared with those of the SED rats (6.15 +/- 0.41 mumol.h-1.g-1). However, only the HI training resulted in a significant increase in the 3-MG transport of the fast-twitch white fibers (HI, 2.37 +/- 0.27; LI, 1.48 +/- 0.11; SED, 1.31 +/- 0.15 mumol.h-1.g-1). Only muscles with an increased citrate synthase activity demonstrated an improved insulin-stimulated glucose transport.(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:Insulin resistance of obese Zucker rats exercise trained at two different intensities. 195 86

The effects of exercise training on glucose-stimulated insulin secretion (GSIS) were studied in male Sprague-Dawley rats made mildly to severely diabetic by partial pancreatectomy. Exercise trained (10 wk treadmill; T) and untrained (Unt) rats were grouped according to posttraining fed-state hyperglycemia as follows: T less than 200 and Unt less than 200 (glucose concn less than 200 mg/dl), T 200-300 and Unt 200-300 (glucose concn 200-300 mg/dl), and T greater than 300 and Unt greater than 300 (glucose concn greater than 300 mg/dl). After exercise training, hyperglycemic glucose clamps were performed in awake rats by elevation of arterial blood glucose concentration 126 mg/dl above fasting basal levels for 90 min. Exercise training significantly increased muscle citrate synthase activity. Prevailing hyperglycemia was reduced during the 10-wk exercise training period in all T rats with fed-state glucose concentrations less than 300, and only 53% of Unt rats in these groups had reduced glycemia. GSIS was significantly higher in T less than 200 [2.4 +/- 0.7 (SD) ng/ml at 90 min] than in Unt less than 200 (1.5 +/- 0.3). A similar response was found for T 200-300 (1.1 +/- 0.3 ng/dl) vs. Unt 200-300 (0.7 +/- 0.1) but not T greater than 300 (0.36 +/- 0.2) vs Unt greater than 300 (0.44 +/- 0.05). Sham-operated control rats had insulin concentrations of 6.6 +/- 1.6 ng/ml at the 90th min of the clamp. Acute exercise reduced fed-state glycemia in rats with mild-to-moderate (less than 300 mg/dl) diabetes.(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:Changes in insulin response to glucose after exercise training in partially pancreatectomized rats. 205 37

The hepatic microsomal fatty acid chain elongation of palmitoyl-CoA and gamma-linolenoyl-CoA was diminished by 40-50% in male Sprague-Dawley rats made diabetic for 2 and 4 weeks following the intravenous administration of a single dose (65 mg/kg) of streptozotocin. Analysis of the activities of the four enzymatic components showed that only one enzyme, the condensing enzyme, which catalyzes the initial and rate-limiting step in chain elongation, was altered by the diabetic state. Both chain elongation and condensation activities were depressed to the same extent, whereas beta-ketoacyl-CoA reductase, beta-hydroxyacyl-CoA dehydrase and trans-2-enoyl-CoA reductase activities were the same as the values obtained with non-diabetic controls. 2 week administration of 10 units of insulin per day to rats which were diabetic for a 2-week period resulted in the reversal of the reduced palmitoyl-CoA elongation and condensation activities to control values. However, neither the condensation nor the elongation of gamma-linolenoyl was reversed by the insulin treatment. These results support the notion of multiple condensing enzymes or chain elongation systems.
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PMID:Enzyme site-specific changes in hepatic microsomal fatty acid chain elongation in streptozotocin-induced diabetic rats. 229 24

The chromatographic separation of amino acids for compositional analysis of peptides and proteins is commonly performed by reverse-phase high-performance liquid chromatography of amino acid residues that have been derivatized with phenylisothiocyanate. The present report describes an extension of this method, which employs thermospray liquid chromatography/mass spectrometry to confirm the identification of the resulting phenylthiocarbamyl (PTC) amino acids. A standard HPLC separation method has been adapted for use with the thermospray technique, and on-column mass spectra of standard synthetic PTC-amino acids have been acquired. These spectra show characteristic fragmentation patterns not seen in the corresponding cyclic phenylthiohydantoin amino acid derivatives. The LC/MS method has been tested on hydrolysates of bovine serum albumin, porcine insulin, and human placental collagen. In each case, the mass spectra of components eluting with the same retention times as the standard PTC-amino acids are similar to those observed in the standard amino acid mixture. Other components display mass spectra that can be interpreted in terms of known in vivo or in vitro modifications to amino acid side chains in these proteins. The LC/MS method has assisted in the identification of by-products of the derivatization reaction. It has also been applied to a study in which an enzyme, citrate synthase, isolated from porcine heart, was compared to the protein expressed by a recombinant porcine citrate synthase gene in Escherichia coli. The data showed that the recombinant protein lacks a modified residue, trimethyllysine, which is present in the enzyme expressed in mammalian tissues.
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PMID:Identification of phenylthiocarbamyl amino acids for compositional analysis by thermospray liquid chromatography/mass spectrometry. 266 8

The early stages of insulin-dependent diabetes mellitus are characterized by a selective inability to secrete insulin in response to glucose, coupled to a better response to nonnutrient secretagogues. The deficient glucose response may be a result of the autoimmune process directed toward the beta-cells. Interleukin-1 (IL-1) has been suggested to be one possible mediator of immunological damage of the beta-cells. In the present study we characterized the sensitivity of beta-cells to different secretagogues after human recombinant IL-1 beta (rIL-1 beta) exposure. Furthermore, experiments were performed to clarify the biochemical mechanisms behind the defective insulin response observed in these islets. Rat pancreatic islets were isolated and kept in tissue culture (medium RPMI-1640 plus 10% calf serum) for 5 days. The islets were subsequently exposed to 60 pM human recombinant IL-1 beta during 48 h in the same culture conditions as above and examined immediately after IL-1 exposure. The rIL-1 beta-treated islets showed a marked reduction of glucose-stimulated insulin release. Stimulation with arginine plus different glucose concentrations, and leucine plus glutamine partially counteracted the rIL-1 beta-induced reduction of insulin release. The activities of the glycolytic enzymes hexokinase, glucokinase, and glyceraldehyde 3-phosphate dehydrogenase, were similar in control and IL-1-exposed islets. Treatment with IL-1 also did not impair the activities of NADH+- and NADPH+-dependent glutamate dehydrogenase, glutamate-aspartate transaminase, glutamate-alanine transaminase, citrate synthase, and NAD+-linked isocitrate dehydrogenase. The oxidation of D-[6-14C]glucose and L-[U-14C]leucine were decreased by 50% in IL-1-treated islets. Furthermore, there was a significant decrease in the ratios of [2-14C]pyruvate oxidation/[1-14C]pyruvate decarboxylation and L-[U-14C]leucine oxidation/L-[1-14C]leucine decarboxylation, indicating that IL-1 decreases the proportion of generated acetyl-coenzyme-A residues undergoing oxidation. However, in the presence of IL-1 there was a significant increase in L-[U-14C]glutamate oxidation. These combined observations suggest that exposure to IL-1 induces a preferential decrease in glucose-mediated insulin release and mitochondrial glucose metabolism. This mitochondrial dysfunction seems to reflect an impairment in proximal steps of the Krebs cycle. It is conceivable that the IL-1-induced suppression and shift in islet metabolism can be an explanation for the beta-cell insensitivity to glucose observed in the early phases of human and experimental insulin-dependent diabetes mellitus.
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PMID:Differential sensitivity to beta-cell secretagogues in cultured rat pancreatic islets exposed to human interleukin-1 beta. 266 6

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

Regional glucose uptake in perfused hearts, and the activities of several glycolytic enzymes contributing to the glucose metabolism in perfused and nonperfused hearts were studied in male and female rats after 8-9 weeks of swimming training. The left ventricular glucose uptake showed a transmural gradient in the sedentary animals, the subendocardial uptake being 30% and 12% higher than that of the subepicardial layer in the males and females, respectively. Swimming exercise abolished the left ventricular glucose uptake gradient in male rats, and in female rats an opposite gradient was found, the subepicardial uptake being 23% higher than the subendocardial uptake. The activities of phosphofructokinase and 3-phosphoglyceraldehyde dehydrogenase also showed transmural gradients in the left ventricles. Training did not abolish these gradients. Training-induced changes in the activities of phosphofructokinase, 3-phosphoglyceraldehyde dehydrogenase, pyruvate kinase, lactate dehydrogenase, glucose-6-phosphate dehydrogenase, citrate synthase, and malate dehydrogenase were found in certain sites of the myocardium. Perfusion of isolated hearts for 50 min with insulin-containing Krebs-Ringer buffer especially affected the activities of phosphofructokinase, lactate dehydrogenase, and citrate synthase, increasing these activities in the left ventricles and decreasing them in the atria. These results indicate that there are regional differences between male and female rats in the cardiac glucose uptake rate after swimming training.
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PMID:Effect of chronic exercise on glucose uptake and activities of glycolytic enzymes measured regionally in rat heart. 273 May 24

This paper describes an organ culture system that maintains frog sartorius muscles in good condition for 5 days. In the absence of serum and insulin, muscles maintained at approximately 93% of resting length atrophied with significant decreases in dry weight, protein content, and contractile force, and in the levels of activity of citrate synthase, lactate dehydrogenase, and creatine kinase. Inclusion of 1.0 mU/ml of insulin in the culture medium prevented the decreases in muscle mass, twitch tension, and citrate synthase activity and minimized the decreases in lactate dehydrogenase, creatine kinase, and tetanic tension. Inclusion of 10% serum, in addition to 1 mU/ml insulin, in the medium did not have clear cut additional benefits. Stretching muscles to 110% of resting length (L0) resulted in marked deterioration with decreases in total protein, enzyme levels, and contractile force. Keeping muscles at approximately 93% L0 was as effective as maintenance at L0 in preventing atrophy and loss of contractile force and enzyme activities. This organ culture procedure, which maintains frog sartorius muscle in good condition without serum for at least 5 days, may provide a useful model for studying the regulatory mechanisms responsible for a variety of adaptations in muscle.
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PMID:Organ culture of frog muscle: maintenance of mass, enzyme levels, and contractile force. 278 58

Muscle homogenates representing slow-twitch oxidative, fast-twitch oxidative-glycolytic, fast-twitch glycolytic, and mixed fiber types were prepared from normal, diabetic, and insulin-treated diabetic rats. Diabetes was induced by injection of 80 mg . kg-1 of streptozotocin. The activities of citrate synthase, succinate dehydrogenase, and 3-hydroxyacyl-CoA dehydrogenase were employed as markers of oxidative potential, whereas phosphorylase, hexokinase, and phosphofructokinase activities were used as an indication of glycolytic capacity. Diabetes was associated with a general decrement in the activity of oxidative marker enzymes for all fiber types except the fast-twitch glycolytic fiber. In contrast, the fast-twitch glycolytic fibers demonstrated the greatest decline in glycolytic enzymatic activity. Insulin-treated animals, either trained or untrained, exhibited enzyme activities similar to their normal counterparts. Exercise training of diabetic rats mimicked the effect of insulin treatment and caused a near normalization of the activity of the marker enzymes. These findings suggest that the enzymatic potential of all skeletal muscle fiber types of diabetic rats may be normalized by exercise training even in the absence of significant amounts of insulin.
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PMID:Influence of training on skeletal muscle enzymatic adaptations in normal and diabetic rats. 293 94


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