Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: EC:4.1.1.32 (phosphoenolpyruvate carboxykinase)
 4,204 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The activity of enzymes involved in glycolysis, gluconeogenesis, and lipoenesis in early and term human placenta was determined. A high activity of pyruvate kinase was found, indicating high glycolytic potential. The activity of this enzyme tended to decrease with gestation. The presence of phosphoenolpyruvate carboxylase activity was detected, suggesting the possibility of gluconeogenesis in the placenta. Very low activity of enzymes involved in fatty acid synthesis was found, whereas the activity of the pentose shunt pathway enzymes, glucose-6-phosphogluconate dehydrogenases, was relatively high. This suggested a role of this pathway in the synthesis of lipids other than fatty acids in the placenta. The activities of enzymes in the human placenta and their changes during gestation where compared to previous observations on enzymes in rat placenta.
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PMID:Enzymes of glucose and fatty acid metabolism in early and term human placenta. 23 82

The incorporation of 14CO into acid-stable assimilation products by Pseudomonas gazotrophia Z-1156 is characterized by a slow rate at the beginning, contrary to the rectilinear kinetics for incorporation of the bicarbonate 14C in the presence of 12CO. The assimilation of 14C-bicarbonate decelerates in the absence of CO. The relative content of 14C is the highest in phosphorylated compounds upon the shortest possible incubation of the cells of P. gazotropha Z-1156 (5 min) in the presence of 14CO and O2, and decreases in the process of incubation. The bulk of radioactivity is found in aspartate and glutamate. The composition of products formed upon the assimilation of 14CO and NaH14CO3 (in the presence of 12CO) during 15 min is similar. The key enzymes of the reductive pentose phosphate cycle have been found in the cell extracts of P. gazotropha A-1156. The specific activity of carboxylating enzymes of the Calvin cycle in the cell extracts increases in the course of proportional growth and sharply decreases when the growth of the culture decelerates. The activity of ribulose diphosphate carboxylase (EC. 4.1.1.39) is always by one-two orders lower than that of ribulose phosphate isomerase (EC. 5.3.1.6) and phosphoribulokinase (EC.2.7.1.19), but is similar to the activity of phosphoenolpyruvate carboxylase (EC. 4.1.1.31). The activity of phosphoenolpyruvate carboxykinase (EC. 4.1.1.32) has not been detected in the cells extracts of P. gazotropha Z-1156.
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PMID:[Biochemical pathways of carbon monoxide assimilation in the carboxydobacterium, Pseudomonas gazotropha]. 66 29

1. Measurements have been made of the activities of enzymes of the glycolytic route, the pentose phosphate pathway, the tricarboxylic acid cycle and lipogenesis in liver and adipose tissue from genetically obese (fa/fa) rats and their lean litter mates (fa/ --). The effect of food restriction for a period of three weeks on the enzyme profile of liver and adipose tissue of the obese rat was also studied. 2. The most striking increases in enzyme activity in livers from obese rats were: (a) among enzymes of lipogenesis; ATP-citrate lyase, acetyl-CoA carboxylase, fatty acid synthetase, malate dehydrogenase (decarboxylating) and cytoplasmic glycerolphosphate dehydrogenase; (b) within the pentose phosphate pathway; glucose-6-phosphate dehydrogenase and 6-phosphogluconate dehydrogenase; (c) within the glycolytic pathway; glucokinase, pyruvate kinase and lactate dehydrogenase. All of these enzymes showed a significant increase in activity on the basis of U/g liver and U/mg DNA. In adipose tissue all the enzymes of lipogenesis, of the glycolytic route, of the oxidative segment of the pentose phosphate pathway and of the tricarboxylic acid cycle were increased when expressed as U/2 fat pads or as U/mg DNA. 3. The restriction of the food intake of obese rats to that consumed by their lean litter mates for periods of three weeks did not produce the expected adaptive decrease in enzymes of lipogenesis; in adipose tissue, only ATP-citrate lyase and malate dehydrogenase (decarboxylating) showed a marked decrease; no significant change was found in adipose tissue or liver of the activities of acetyl-CoA carboxylase and fatty acid synthetase, when expressed on a cell basis (U/mg DNA). The non-oxidative enzymes of the pentose phosphate pathway and enzymes involved in glycerogenesis (pyruvate carboxylase, malate dehydrogenase and phosphoenolpyruvate carboxykinase) all increased in adipose tissue from limit-fed obese rats. 4. The rate of conversion of specifically labelled glucose to (14C)O2 and 14C-labelled lipid by pieces of adipose tissue and by liver slices was also measured. Insulin caused an increase in the conversion of (1-14C)glucose to (14C)O2 and 14C-labelled lipid in obese rats fed ad libitum, limit-fed rats and in their lean litter mates. 5. The results are discussed in relation to the raised insulin and hypothyroid state of the obese rat. The effect of this altered hormonal status on the activity of cyclic nucleotide phosphodiesterases and cellular levels of adenosine 3' :5'-monophosphate and guanosine 3' :5'-monophosphate and guanosine 3' :5'-monophosphate in relation to the obese syndrome is considered.
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PMID:Adaptive responses of enzymes of carbohydrate and lipid metabolism to dietary alteration in genetically obese Zucker rats (fa/fa). 71 Mar 95

The effect of human recombinant tumor necrosis factor (TNF)-alpha on enzymes of gluconeogenesis in the rat was investigated by determining the activity of glucose 6-phosphatase, fructose 1,6-diphosphatase (FDP), and phosphoenolpyruvate carboxykinase in the liver and kidney of fed and fasted rats. The activity of transaldolase in the pentose phosphate pathway was also measured. Starvation of rats for 24 hr resulted in a 1.6- to 3.1-fold increase in liver and kidney glucose 6-phosphatase and phosphoenolpyruvate carboxykinase (P less than or equal to 0.05), a decrease in liver and kidney FDP (P less than 0.002), and an increase in liver and kidney transaldolase (P = 0.0001). Injection of 50 and 100 micrograms/kg/day of TNF for 5 days resulted in a significant (P less than or equal to 0.03) decrease in kidney FDP only. Injection of 100 micrograms/kg/day of TNF for 5 days with a 24-hr fast on Day 5 resulted in a significant (P = 0.04) increase in liver transaldolase, and a significant decrease in kidney FDP and phosphoenolpyruvate carboxykinase. Comparison of the enzyme activities of rats injected with 100 micrograms/kg/day of TNF for 5 days with those of their pair-fed control partners revealed additionally a significant decrease in glucose 6-phosphatase in the liver (P less than 0.001). It is concluded that TNF administration in the rat has different effects on the enzymes of gluconeogenesis in the liver and kidney, and these effects differ from those seen in starved or tumor-bearing rats.
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PMID:Effect of tumor necrosis factor on enzymes of gluconeogenesis in the rat. 130 99

LLC-PK1 cells, derived from pig kidney, retain several properties of the proximal tubule, but are incapable of gluconeogenesis, due to the lack of fructose-1,6-bisphosphatase (FBPase) [Am. J. Physiol. 248 (Cell Physiol. 17): C181-185, 1985]. Cells incapable of gluconeogenesis require a hexose, pentose, or nucleoside to provide ribose-5-phosphate for RNA biosynthesis. To induce or select cells that express FBPase activity, we cultured LLC-PK1 cells in glucose-free medium. We obtained cells (designated LLC-PK1-FBPase+) that express FBPase activity and are capable of growing in the complete absence of sugars or nucleosides. The cells have apical membrane enzyme activities that differ from those of wildtype cells. Tests of metabolic flow through the gluconeogenic pathway, using 3-mercaptopicolinic acid, a specific inhibitor of phosphoenolpyruvate carboxykinase, confirmed that the cells are gluconeogenic. LLC-PK1-FBPase+ cells grown in medium containing 5 mM glucose for five weekly passages continued to express FBPase activity and apical membrane enzyme activities characteristic of the FBPase+ strain. When switched back to glucose-free medium, they proliferated well. The strain appears to be stable. It should provide a model for studying the relationship between gluconeogenesis and other proximal tubule functions. An incidental finding is that in both strains, the activity of lactate dehydrogenase varied directly with the concentration of glucose in the growth medium, indicating that the expression of lactate dehydrogenase may be regulated by glucose or a metabolite of glucose.
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PMID:Isolation, growth, and characterization of a gluconeogenic strain of renal cells. 303 Jan 22

The literature concerning the metabolism of carbon and nitrogen compounds in ectomycorrhizal associations of trees is reviewed. The absorption and translocation of mineral ions by the mycelia require an energy source and a reductant which are both supplied by respiratory catabolism of carbohydrates produced by the host plant. Photosynthates are also required to generate the carbon skeletons for amino acid and carbohydrate syntheses during the growth of the mycelia. Competition for photosynthates occurs between the fungal cells and the various vegetative sinks in the host tree. The nature of carbon compounds involved in these processes, their routes of metabolism, the mechanisms of control and the partitioning of metabolites between the various sites of utilization are only poorly understood. Both ascomycetous and basidiomycetous ectomycorrhizal fungi synthesize and some, if not all, accumulate mannitol, trehalose and triglycerides. The fungal strains employ the Embden--Meyerhof pathway of glucose catabolism and the key enzymes of the pentose phosphate pathway (6-phosphogluconate dehydrogenase, glucose-6-phosphate dehydrogenase, transaldolase and transketolase). Anaplerotic CO2 fixation, via pyruvate carboxylase and/or phosphoenolpyruvate carboxykinase, provides high pools of amino acids. This process could be important in the recapture and assimilation of respired CO2 in the rhizosphere. The ectomycorrhizas are thought to contain the Embden--Meyerhof pathway, the pentose phosphate pathway and the tricarboxylic acid cycle, which provide the carbon skeletons for the assimilation of ammonia into amino acids. The main route of assimilation of ammonia appears to be through the glutamine synthetase-glutamate synthase cycle in the ectomycorrhizas. Glutamate dehydrogenase plays a minor role in this process. Glutamate dehydrogenase and glutamine synthetase are present in free-living ectomycorrhizal fungi and they participate in the assimilation of ammonia and the synthesis of amino acids through the glutamate dehydrogenase/glutamine synthetase sequence. In both in vitro cultures of fungi and ectomycorrhizas, the assimilated nitrogen accumulates in glutamine. Glutamine, but also ammonia, are thought to be exported from the fungal tissues to the host cells. Studies on the metabolism of ectomycorrhizas and ectomycorrhizal fungi have focused on the metabolic pathways and compounds which accumulate in the symbiotic tissues. Studies on regulation of the overall process, and the control of enzyme activity in particular, are still fragmentary.(ABSTRACT TRUNCATED AT 400 WORDS)
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PMID:Carbon and nitrogen metabolism in ectomycorrhizal fungi and ectomycorrhizas. 312 Jul 92

Hepatocytes were isolated from the livers of fed rats and incubated, in the presence and absence of 100 nM-glucagon, with a substrate mixture containing glucose (10 mM), fructose (4 mM), alanine (3.5 mM), acetate (1.25 mM), and ribose (1 mM). In any given incubation one substrate was labelled with 14C. Incorporation of 14C into glucose, glycogen, CO2, lactate, alanine, glutamate, lipid glycerol and fatty acids was measured after 20 and 40 min of incubation under quasi-steady-state conditions [Borowitz, Stein & Blum (1977) J. Biol. Chem. 252, 1589-1605]. These data and the measured O2 consumption were analysed with the aid of a structural metabolic model incorporating all reactions of the glycolytic, gluconeogenic, and pentose phosphate pathways, and associated mitochondrial and cytosolic reactions. A considerable excess of experimental measurements over independent flux parameters and a number of independent measurements of changes in metabolite concentrations allowed for a stringent test of the model. A satisfactory fit to the data was obtained for each condition. Significant findings included: control cells were glycogenic and glucagon-treated cells glycogenolytic during the second interval; an ordered (last in, first out) model of glycogen degradation [Devos & Hers (1979) Eur. J. Biochem. 99, 161-167] was required in order to fit the experimental data; the pentose shunt contributed approx. 15% of the carbon for gluconeogenesis in both control and glucagon-treated cells; net flux through the lower Embden-Meyerhof pathway was in the glycolytic direction except during the 20-40 min interval in glucagon-treated cells; the increased gluconeogenesis in response to glucagon was correlated with a decreased pyruvate kinase flux and lactate output; fluxes through pyruvate kinase, pyruvate carboxylase, and phosphoenolpyruvate carboxykinase were not coordinately controlled; Krebs cycle activity did not change with glucagon treatment; flux through the malic enzyme was towards pyruvate formation except for control cells during interval II; and 'futile' cycling at each of the five substrate cycles examined (including a previously undescribed cycle at acetate/acetyl-CoA) consumed about 26% of cellular ATP production in control hepatocytes and 21% in glucagon-treated cells.
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PMID:Quantitative analysis of intermediary metabolism in hepatocytes incubated in the presence and absence of glucagon with a substrate mixture containing glucose, ribose, fructose, alanine and acetate. 391 12

Metabolic alterations in ventromedial hypothalamus (VMH)-lesioned rats were investigated by examining daily changes of enzyme activities and urea concentrations three weeks after the operation. VMH-lesions in female adult rats caused a significant elevation in the activity of acetyl-CoA carboxylase in the liver and parametrial adipose tissue. These changes suggest an increased lipogenesis. VMH-lesions also elicited an increase in activities of glucokinase (GK), pyruvate kinase (PK) and fructose 1,6-bisphosphatase (FBPase), and a decrease in activities of phosphofructokinase (PFK), glucose-6-phosphatase (G6Pase) and phosphoenolpyruvate carboxykinase (PEPCK) in the liver. The apparently inconsistent changes in activities of key glycolytic enzymes, GK, PK and PFK, and key gluconeogenic enzymes, G6Pase, PEPCK and FBPase in the liver may be explained by the fact that they were favorable for glucose oxidation through pentose phosphate cycle and provide NADPH for lipogenesis in the liver. Furthermore, VMH-lesions induced an increase in urea contents of the liver and serum, and elicited an increase in activity of liver tyrosine aminotransferase (TAT) and a decrease in activity of liver histidase. These changes suggest an accelerated amino acid and protein catabolism, and favor an increment in the supply of the substrate for lipogenesis. Daily rhythms of TAT, histidase activities and serum urea concentration observed in the control rats were abolished by VMH-lesions. These findings suggest that VMH-lesions elicit the loss of these daily rhythms, probably through the disturbance of the circadian rhythm of feeding behavior at this dynamic phase (three weeks after operation) of obesity.
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PMID:Shift of metabolism in rats with ventromedial hypothalamic lesions with respect to changes in daily rhythms of enzyme activity. 614 67

Previous studies indicated that in pancreatic islets the amount of glucose-derived pyruvate that enters mitochondrial metabolism via carboxylation is approximately equal to that entering via decarboxylation and that both carboxylation and decarboxylation are correlated with capacitation of glucose metabolism and insulin release. The relatively high rate of carboxylation is consistent with the current study's finding that pyruvate carboxylase is as abundant in pancreatic islets as it is in liver and kidney. Since islets do not contain phosphoenolpyruvate carboxykinase and, therefore, cannot carry out glyconeogenesis from pyruvate, the carboxylase might be present in the islet to participate in novel anaplerotic reactions. This idea was first explored by incubating mitochondria from various tissues with pyruvate. Mitochondria from tissues, such as pancreatic islets, liver, and kidney, in which pyruvate carboxylase is abundant, exported a large amount of malate and little or no citrate, isocitrate, and aspartate to the medium. The amount of malate within the mitochondria was < 1% that in the medium. When pancreatic islet mitochondria were incubated with [1-14C]pyruvate, radioactive carbon appeared in the medium primarily in malate. Very little radioactivity appeared in amino acids, and little or no radioactivity appeared in citrate and isocitrate. Carbon 1 of pyruvate can be incorporated into malate and other citric acid cycle intermediates only via carboxylation, as this carbon would be lost via decarboxylation when pyruvate enters the citric acid cycle as acetyl-CoA via the pyruvate dehydrogenase reaction. The amount of malate formed equaled the 14CO2 formed and the radioactivity from C-1 of pyruvate recovered in malate slightly exceeded the formation of 14CO2 in agreement with our previous studies that reported a high rate of carboxylation of pyruvate in intact islets. When intact pancreatic islets were incubated with methyl [U-14C]succinate as a mitochondrial source of four-carbon dicarboxylic acids, radioactivity appeared in pyruvate and lactate. Taken together with previous studies, the current results suggest that during glucose-induced insulin secretion there is a shuttle operating across the mitochondrial membrane in which glucose-derived pyruvate is taken up by mitochondria and carboxylated to oxaloacetate by pyruvate carboxylase. The oxaloacetate is converted to malate which exits the mitochondrion, where, in the cytosol, it is decarboxylated to pyruvate in the reaction catalyzed by malic enzyme. This pyruvate re-enters mitochondrial pools. Such a cycle produces NADPH in the cytosol. Since it is a cycle, this shuttle can produce far more NADPH than the pentose phosphate pathway, which is known to be a very minor route of glucose metabolism in the islet.(ABSTRACT TRUNCATED AT 400 WORDS)
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PMID:Feasibility of a mitochondrial pyruvate malate shuttle in pancreatic islets. Further implication of cytosolic NADPH in insulin secretion. 765 22

Coryneform bacteria are widely used to produce amino acids, in particularly glutamic acid, by fermentation. To study the metabolic fate of glucose as the carbon source, we developed a method to analyze intracellular extracts by NMR and HPLC. The intracellular metabolites represent the metabolic state of the cells. Glutamic acid was the major metabolic intermediate found in the extracts and its 13C isotopic enrichment reflected that of pyruvic acid. Thus, it was possible to determine the respective contributions of the two major glucose catabolic pathways during the exponential growth phase; glycolysis (55%) and the pentose phosphate pathway (45%). Absolute glutamate 13C enrichments resulting from the incorporation of [1-13C]glucose were determined to quantify the contribution of several metabolic pathways such as anaplerotic pathways (61%; phosphoenolpyruvate carboxylase, pyruvate carboxylase, malic enzyme), a single turn (32%) or multiple turns of the Krebs cycle and the glyoxylate shunt, to oxaloacetate synthesis. A previously described model was adapted to C. melassecola for these calculations. The Krebs cycle was active, whereas the glyoxylate shunt was inactive in exponentially growing cells of C. melassecola with glucose as the sole carbon source. The contributions of anaplerotic enzymes and pyruvate dehydrogenase to replenishing the Krebs' cycle were determined to be 38% and 62%, respectively.
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PMID:13C-NMR studies of Corynebacterium melassecola metabolic pathways. 785 27


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