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Query: EC:4.1.1.49 (phosphoenolpyruvate carboxykinase)
 4,654 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

In addition to the normal carboxylation reaction, phosphoenolpyruvate carboxylase from Zea mays catalyzes a HCO3(-)-dependent hydrolysis of phosphoenolpyruvate to pyruvate and Pi. Two independent methods were used to establish this reaction. First, the formation of pyruvate was coupled to lactate dehydrogenase in assay solutions containing high concentrations of L-glutamate and aspartate aminotransferase. Under these conditions, oxalacetic acid produced in the carboxylation reaction was efficiently transaminated, and decarboxylation to form spurious pyruvate was negligible. Second, sequential reduction of oxalacetate and pyruvate was achieved by initially running the reaction in the presence of malate dehydrogenase with NADH in excess over phosphoenolpyruvate. After the reaction was complete, lactate dehydrogenase was added, thus giving a measure of pyruvate concentration. At pH 8.0 in the presence of Mg2+, the rate of phosphoenolpyruvate hydrolysis was 3-7% of the total reaction rate. The hydrolysis reaction catalyzed by phosphoenolpyruvate carboxylase was strongly metal dependent, with rates decreasing in the order Ni2+ greater than Co2+ greater than Mn2+ greater than Mg2+ greater than Ca2+. These results suggest that the active site metal ion binds to the enolate oxygen, thus stabilizing the proposed enolate intermediate. The more stable the enolate, the less reactive it is toward carboxylation and the greater the opportunity for hydrolysis.
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PMID:Hydrolysis of phosphoenolpyruvate catalyzed by phosphoenolpyruvate carboxylase from Zea mays. 163 56

The activities of glucose-6-phosphatase (G6Pase), fructose-1,6-bisphosphatase (FBPase), phosphoenolpyruvate carboxykinase (PEPCK) and pyruvate carboxylase (PC) were determined in homogenates of adult Schistosoma mansoni worms and compared with the activities in homogenates of rat liver and rat skeletal muscle, tissues with a high and a low gluconeogenic capacity, respectively. All four gluconeogenic enzymes were present in S. mansoni. The enzymes were less active than in rat liver, but the activities of G6Pase, PEPCK and PC were at least an order of magnitude higher than in rat skeletal muscle whereas FBPase was approximately equally active in S. mansoni and in rat muscle. Experiments with 14C-labelled substrates or [14C]NaHCO3 failed to demonstrate the actual occurrence of gluconeogenesis in S. mansoni. Some possible other functions of the gluconeogenic enzymes were investigated. Experiments with inhibitors of PEPCK gave no indications that this enzyme was involved in the degradation of glucose. This was confirmed by 13C-NMR experiments which indicated that lactate was formed from phosphoenolpyruvate via the actions of pyruvate kinase and lactate dehydrogenase, and that PEPCK did not participate in the formation of lactate. Substrate cycling between fructose-6-dehydrogenase, and fructose-1,6-bisphosphate was demonstrated to occur in adult S. mansoni. This shows that FBPase participates in the glucose metabolism of this parasite.
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PMID:The enigmatic presence of all gluconeogenic enzymes in Schistosoma mansoni adults. 164 28

This study investigated the hypothesis that dehydroepiandrosterone (DHEA) functions as an antiobesity agent by promoting energy wastage via hepatic substrate cycling in prediabetic male BHE/cdb rats. Weanling BHE/cdb rats fed a 65% glucose diet were injected intraperitoneally daily with either DHEA (0.35 mol/kg body wt) or vehicle (1 mL/kg body wt) for 7 wk. The DHEA treatment significantly (P less than 0.05) reduced body weight gain. The DHEA-treated rats had epididymal and retroperitoneal fat pads that were 40% and 66% lighter, respectively, than those of control rats. The residual carcasses (i.e., minus fat pads, liver and ingesta) of DHEA-treated rats contained a significantly lower percentage of fat than those of control rats. The DHEA treatment significantly reduced fasting serum glucose and triglycerides without affecting total or HDL cholesterol. Isolated hepatocytes from DHEA-treated rats converted 2.5 times as much [U-14C]glucose to 14CO2 and one-half as much alanine to glucose as did hepatocytes from control rats. The DHEA treatment increased the specific activities of malic enzyme and lactate dehydrogenase 4.0- and 1.8-fold, respectively. Hepatocytes from DHEA-treated rats tended (P less than 0.08) to have lower phosphoenolpyruvate carboxykinase activities than hepatocytes from control rats. These data suggest that DHEA treatment exerts some of its antiobesity and antidiabetic effects in prediabetic, lipemic BHE/cdb rats by promoting hepatic glucose oxidation and reducing gluconeogenesis.
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PMID:Antiobesity effects of dehydroepiandrosterone are mediated by futile substrate cycling in hepatocytes of BHE/cdb rats. 183 18

The activities of selected enzymes of carbohydrate metabolism were measured in tetrathyridia of Mesocestoides corti and in adult females and males of Heterakis spumosa. When the species were compared, only lactate dehydrogenase and phosphoenolpyruvate carboxykinase activities were considerably higher in M. corti. Activities of other enzymes were higher in H. spumosa, with malate dehydrogenase activity being considerably so. In H. spumosa, enzyme activity was higher, and succinate dehydrogenase markedly so in males, when compared with females. Tetrathyridia aged 170 and 210 days show relatively stable malate and lactate dehydrogenase activities, and mice of ICR and BALB/c strains are suitable for the maintenance of tetrathyridia.
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PMID:Some enzymes of carbohydrate metabolism in Mesocestoides corti and Heterakis spumosa. 194 Feb 48

Treatment of rats with diazinon (40 mg/kg, i.p.) resulted in hyperglycaemia and depletion of glycogen from the brain and peripheral tissues two hours after administration. The activities of glycogen phosphorylase and phosphoglucomutase were significantly higher in the brain and liver; that of glucose-6-phosphatase was not altered. The activities of the glycolytic enzymes hexokinase and lactate dehydrogenase were increased only in the brain. The cholinesterase activity in the brain was reduced by treatment with diazinon. The activities of the hepatic gluconeogenic enzymes fructose 1,6-diphosphatase and phosphoenolpyruvate carboxykinase were significantly increased. The lactate level was increased in the brain and blood, whereas that of pyruvate was not changed. The activity of glucose-6-phosphate dehydrogenase was not changed to any major extent. Cholesterol and ascorbic acid contents of adrenals were depleted in diazinon-treated animals. The changes were pronounced after intraperitoneal administration of 40 mg/kg diazinon, they were slight but significant after 20 mg/kg, and absent after 10 mg/kg. Hyperglycaemia and changes in carbohydrate metabolism were abolished by adrenalectomy suggesting possible involvement of adrenals.
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PMID:The role of adrenals in diazinon-induced changes in carbohydrate metabolism in rats. 209 50

Treatment with diazinon (40 mg/kg, i.p.) resulted in hyperglycemia and depletion of glycogen from cerebral and peripheral tissues 2 hr after its administration in rats. The activities of the glycogenolytic enzymes glycogen phosphorylase and phosphoglucomutase were increased significantly in brain and liver, whereas that of glucose-6-phosphatase was not altered. The activities of the glycolytic enzymes hexokinase and lactate dehydrogenase were increased only in the brain. The cholinesterase activity of the brain was reduced by treatment with diazinon. The activities of the hepatic gluconeogenic enzymes fructose 1,6-diphosphatase and phosphoenolpyruvate carboxykinase were also increased significantly in diazinon-treated animals. The level of lactate was increased in brain and blood, whereas that of pyruvate was not changed. The activity of glucose-6-phosphate dehydrogenase was not changed significantly. The cholesterol and ascorbic acid contents of adrenals were depleted in diazinon-treated animals. The hyperglycemia and changes in carbohydrate metabolism were abolished by adrenalectomy, suggesting the possible involvement of the adrenals in the induced changes in diazinon-treated animals.
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PMID:Modification of diazinon-induced changes in carbohydrate metabolism by adrenalectomy in rats. 234 75

Renal proximal tubular epithelia were used to assess the factors responsible for the induction of glycolysis in cultured cells. Primary cultures of rabbit proximal tubules, which achieved confluency at 6 days, exhibited hormonal responsiveness and brush-border characteristics typical of proximal tubular cells. Beginning at day 4, these cultured cells exhibited increased glycolytic metabolism reflected by enhanced glucose uptake and lactate production, along with parallel increases in activity of the glycolytic enzymes, pyruvate kinase and lactate dehydrogenase. The gluconeogenic enzymes, phosphoenolpyruvate carboxykinase (PEPCK) and fructose-1,6-bisphosphatase (FDP), were downregulated, and the cultured cells exhibited lower oxygen consumption rates than fresh tubules. Cells grown on a rocker, to mitigate hypoxia, exhibited a metabolic and enzymatic profile similar to cells grown under still conditions. ATP levels in cultured cells were higher than in fresh tubules. Furthermore, pyruvate kinase activity was higher in cells grown in media containing 0.5 as contrasted with 25 mM glucose. The enhanced glycolytic metabolism exhibited by cultured proximal tubular cells appears to be a characteristic of proliferation and is not a response to hypoxia, the Pasteur effect, or environmental glucose.
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PMID:Carbohydrate metabolism by primary cultures of rabbit proximal tubules. 253 63

1. The activities of phosphoenolpyruvate carboxykinase, malic enzyme, NAD+ and NADP+ isocitrate isocitrate dehydrogenase, glucose-6-phosphate dehydrogenase, lactate dehydrogenase and pyruvate kinase were assayed in homogenate of camel hump and sheep tail tissues. 2. In addition the levels of glucose, cholesterol, total protein and total lipids in these tissues were measured. 3. Results obtained were utilized to compare the state of metabolism of adipose tissue of camel hump to that of sheep tail, and to shed some light on possible contribution of these tissues toward blood glucose level.
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PMID:A comparative study of enzyme profile of camel (Camelus dromedarius) hump and sheep (Ovis aries) tail tissues. 280 43

Cell-free extracts of two strictly anaerobic mollicutes, Anaeroplasma intermedium 5LA and Asteroleplasma anaerobium 161T, were tested for enzymic activities of intracellular carbohydrate metabolism. Asteroleplasma anaerobium was also tested for enzymes of purine and pyrimidine metabolism. Both organisms had enzymic activities associated with the nonoxidative portion of the pentose phosphate pathway, and with the Embden-Meyerhoff-Parnas pathway. The 6-phosphofructokinase (PFK) of Asteroleplasma anaerobium was ATP-dependent, whereas the PFK of Anaeroplasma intermedium was PPi-dependent. The two anaerobic mollicutes also differed with respect to the enzymes that converted phosphoenolpyruvate (PEP) to pyruvate; Anaeroplasma intermedium had pyruvate kinase activity, but Asteroleplasma anaerobium had pyruvate, orthophosphate dikinase activity (PPi-dependent). Both organisms had lactate dehydrogenase activity which was activated by fructose 1,6-bisphosphate (Fru-1,6-P2). Anaeroplasma intermedium had activity for PEP carboxykinase (activated by Fru-1,6-P2), but Asteroleplasma anaerobium did not. PEP carboxytransphosphorylase activity was not detected in either organism. Anaeroplasma intermedium had malate dehydrogenase and isocitrate dehydrogenase activities, but it had no activities for the three other tricarboxylic acid cycle enzymes examined; Asteroleplasma anaerobium had malate dehydrogenase activity only. Asteroleplasma anaerobium had enzymic activities for the interconversion of purine nucleobases, (deoxy)ribonucleosides, and (deoxy)ribomononucleotides, including PPi-dependent nucleoside kinase, reported heretofore only in some other mollicutes. Asteroleplasma anaerobium could synthesize dTDP by the thymine salvage pathway if deoxyribose 1-phosphate was provided, and it had dUTPase, ATPase, and dCMP kinase activities. It lacked (deoxy)cytidine deaminase, dCMP deaminase, and deoxycytidine kinase activities.
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PMID:Enzymic activities of carbohydrate, purine, and pyrimidine metabolism in the Anaeroplasmataceae (class Mollicutes). 281 26

Treatment with diazinon resulted in hyperglycaemia and depletion of glycogen from cerebral and peripheral tissues 2 h after its administration in rats; the changes were maximal after 40 mg/kg diazinon, administered intraperitoneally. The activities of glycogen phosphorylase and phosphoglucomutase were significantly increased in brain and liver, while that of glucose-6-phosphatase was not altered. The activities of the glycolytic enzymes hexokinase and lactate dehydrogenase were increased only in brain. The cholinesterase activity of the brain was reduced by treatment with diazinon. The activities of hepatic gluconeogenic enzymes (fructose 1,6 diphosphatase and phosphoenolpyruvate carboxykinase) were also significantly increased in diazinon-treated animals. The level of lactate was increased in brain and blood while that of pyruvate was not changed. The activity of glucose-6-phosphate dehydrogenase was not significantly changed. Cholesterol and ascorbic acid contents of adrenals were depleted in diazinon-treated animals. Adrenalectomy abolished the hyperglycaemia and changes in carbohydrate metabolism, suggesting the possible involvement of adrenals in the induced changes in diazinon-treated animals.
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PMID:Effect of adrenalectomy on diazinon-induced changes in carbohydrate metabolism. 281 1


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