Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: EC:6.4.1.1 (pyruvate carboxylase)
 1,516 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Mechanisms have been examined by which hyperosmotic blood plasma might elevate the levels of aspartate and glutamate in the brain of the toad Bufo boreas. CO2 fixation was assessed by two in vivo methods using [2-14 C]glucose injected intracisternally. Thirty minutes after injection, the 14C labeling of glutamate and aspartate was more than 100 times greater in brain than in liver. In brain tissues, 40 + % of 14C atoms appeared to be incorporated into aspartate via the pyruvate carboxylase pathway. Brain tissues of control toads and toads adapting or adapted to hyperosmotic plasma osmolality revealed no differences in the rate of CO2 fixation as related to glucose utilization or tissue pool sizes of glutamate and aspartate. Elevated levels of these amino acids in blood plasma preceded increases in brain tissues. Carbon atoms required during hyperosmotic adaptation for expansion of amino acid pools in brain tissues may, in part, originate from amino acids in blood but apparently not from CO2 fixation in brain.
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PMID:Role of carbon dioxide fixation, blood aspartate and glutamate in the adaptation of amphibian brain tissues to a hyperosmotic internal environment. 678 98

1. The metabolism of L-alanine was studied in isolated guinea-pig kidney-cortex tubules. 2. In contrast with previous conclusions of Krebs [(1935) Biochem. J. 29, 1951-1969], glutamine was found to be the main carbon and nitrogenous product of the metabolism of alanine (at 1 and 5 mM). Glutamate and ammonia were only minor products. 3. At neither concentration of alanine was there accumulation of glucose, glycogen, pyruvate, lactate, aspartate or tricarboxylic acid-cycle intermediates. 4. Carbon-balance calculations and the release of 14CO2 from [U-14C]alanine indicate that oxidation of the alanine carbon skeleton occurred at both substrate concentrations. 5. A pathway involving alanine aminotransferase, glutamate dehydrogenase, glutamine synthetase, pyruvate dehydrogenase, pyruvate carboxylase and enzymes of the tricarboxylic acid cycle is proposed for the conversion of alanine into glutamine. 6. Strong evidence for this pathway was obtained by: (i) suppressing alanine removal by amino-oxyacetate, and inhibitor of transaminases, (ii) measuring the release of 14CO2 from [1-14C]alanine, (iii) the use of L-methionine DL-sulphoximine, an inhibitor of glutamine synthetase, which induced a large increase in ammonia release from alanine, and (iv) the use of fluoroacetate, an inhibitor of aconitase, which inhibited glutamine synthesis with concomitant accumulation of citrate from alanine. 7. In this pathway, the central role of pyruvate carboxylase, which explains the discrepancy between our results and those of Krebs (1935), was also demonstrated.
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PMID:The conversion of alanine into glutamine in guinea-pig renal cortex. Essential role of pyruvate carboxylase. 733 38

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

Carbon-13 NMR spectroscopy was used to study the effects of the peroxisome proliferator perfluoro-n-decanoic acid (PFDA) on hepatic carbohydrate metabolism in male Fischer-344 rats. The data indicate that PFDA-treated rats display an inhibition in hepatic [1-13C]glucose and [3-13C]alanine utilization on day 5 posttreatment. PFDA rats show hepatic mean glucose and alanine intensities which are significantly greater (ca. 10-100%) than controls. With [1-13C]-glucose as substrate, PFDA rats show severe to complete inhibition in glycogenesis on days 3 and 5 posttreatment. With [3-13C]alanine as substrate, both groups show functional gluconeogenesis and glycogenesis; however, treated rats show a more transient and less intense C1-glycogen resonance relative to control. These data suggest that PFDA inhibits either the hepatocellular transport of glucose and/or its phosphorylation by glucokinase. The effect of PFDA on TCA cycle activity was determined by monitoring the flow of [3-13C]alanine into glutamate. The relative activity of pyruvate carboxylase (PC) versus pyruvate dehydrogenase (PDH) is represented by the ratio of the glutamate NMR signal intensities (C2 + C3)/C4. PFDA rats show a lower (C2 + C3)/C4 glutamate ratio, suggesting greater relative activity of PDH versus PC in PFDA rats relative to controls. Differences in PDH activity may arise from differences in lipolytic activity. Our data suggest a dysfunction in fatty acid metabolism in PFDA rats and corroborate other studies which show that PFDA inhibits fatty acid oxidation.
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PMID:Effects of the peroxisome proliferator perfluoro-n-decanoic acid on hepatic gluconeogenesis and glycogenesis: a 13C NMR investigation. 815 20

Carbon metabolism was investigated in cerebellar and cortical astrocytes cultured for 15 or 35 days. The consumption rates of exogenous carbon sources--amino acids and glucose--and the production rates of exported metabolites--citrate, lactate, alanine and glutamine--were determined. The specific 13C-enrichment of lactate and glutamine carbons were determined after cell incubation with [1-13C]glucose. These data were used to evaluate the fluxes through metabolic pathways using a monocompartmental model of the cell metabolism including glycolysis and tricarboxylic acid cycle related pathways. The model concluded to a very large contribution of fatty acids as an endogenous carbon source of acetyl-CoA. As a consequence of the high fatty acid turn-over, there was an important recycling (via pyruvate) of the oxaloacetate molecules generated by citrate lyase activity. This recycling represented in fact the major part of the pyruvate carboxylase activity, which therefore was not directly related to metabolite export. Comparing the data from cerebellar and cortical astrocytes evidenced, on the other hand, some differences in metabolite contents which could be related to different cell maturation stages linked to their different tissular origins.
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PMID:Analysis of carbon metabolism in cultured cerebellar and cortical astrocytes. 929 87

Nuclear magnetic resonance spectroscopy was utilized to study the metabolism of [1-(13)C]glucose in mycelia of the ectomycorrhizal ascomycete Sphaerosporella brunnea. The main purpose was to assess the biochemical pathways for the assimilation of glucose and to identify the compounds accumulated during glucose assimilation. The majority of the (13)C label was incorporated into mannitol, while glycogen, trehalose and free amino acids were labeled to a much lesser extent. The high enrichment of the C1/C6 position of mannitol indicated that the polyol was formed via a direct route from absorbed glucose. Randomization of the (13)C label was observed to occur in glucose and trehalose leading to the accumulation of [1,6-(13)C]trehalose and [1,6-(13)C]glucose. This suggests that the majority of the glucose carbon used to form trehalose was cycled through the metabolically active mannitol pool. The proportion of label entering the free amino acids represented 38% of the soluble (13)C after 6 hours of continuous glucose labeling. Therefore, amino acid biosynthesis is an important sink of assimilated carbon. Carbon-13 was incorporated into [3-(13)C]alanine and [2-(13)C]-, [3-(13)C]-, and [4-(13)C]glutamate and glutamine. From the analysis of the intramolecular (13)C enrichment of these amino acids, it is concluded that [3-(13)C]pyruvate, arising from [1-(13)C]glucose catabolism, was used by alanine aminotransferase, pyruvate dehydrogenase, and pyruvate carboxylase (or phosphoenolpyruvate carboxykinase). Intramolecular (13)C labeling patterns of glutamate and glutamine were similar and are consistent with the operation of the Krebs cycle. There is strong evidence for (a) randomization of the label on C2 and C3 positions of oxaloacetate via malate dehydrogenase and fumarase, and (b) the dual biosynthetic and respiratory role of the citrate synthase, aconitase, and isocitrate dehydrogenase reactions. The high flux of carbon through the carboxylation (presumably pyruvate carboxylase) step indicates that CO(2) fixation is an important component of the carbon metabolism in S. brunnea, and it is likely that this anaplerotic role is particularly prevalent during NH(4) (+) assimilation. The most relevant information resulting from this investigation is (a) the occurrence of the mannitol cycle, (b) a large part of the trehalose pool is synthesized after the cycling of glucose-carbon through the mannitol cycle, and (c) pyruvate (or phosphoenolpyruvate) carboxylation plays an important role in the primary metabolism of glucose-fed mycelia.
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PMID:Carbohydrate and Amino Acid Metabolism in the Ectomycorrhizal Ascomycete Sphaerosporella brunnea during Glucose Utilization : A C NMR Study. 1666 12

Carbon metabolism in the rat brain was studied in animals anesthetized with a light dose of pentobarbital and in awake animals under morphine, which were infused with either [1-13C]glucose+acetate or glucose+[2-13C]acetate for various periods of time. Brain amino-acid enrichments in tissue extracts were determined by nuclear magnetic resonance (NMR) spectroscopy and their time evolution was analyzed by automatic fitting. Acetyl-coenzyme A C2 enrichment and ratio between pyruvate carboxylase and pyruvate dehydrogenase activity (PC/PDH) were determined from glutamate and glutamine labeling. The following results were obtained: (i) amino-acid enrichment patterns implied metabolic compartmentation and occurrence of the glutamate-glutamine cycle; (ii) kinetics of aspartate, GABA, and glutamate labeling from [1-13C]glucose and of glutamine labeling from [2-13C]acetate indicated a twofold higher metabolic activity in awake than in anesthetized rat brain; (iii) evaluation of the contributions of the astrocytic and neuronal metabolisms to glutamine synthesis in both groups of rats indicated a coupling between neuronal tricarboxylic acid (TCA) cycle, glutamate-glutamine cycle and glial TCA cycle; and (iv) analyzing the extrapolations back to time zero and the steady-state values of PC/PDH indicated a close coupling between PC activity and both astrocytic and neuronal TCA cycles. All these results suggest a cooperative-like behavior of astrocytic and neuronal metabolisms to fulfill the anabolic and energy needs linked to brain activation.
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PMID:Close coupling between astrocytic and neuronal metabolisms to fulfill anaplerotic and energy needs in the rat brain. 1794 May 39

Conversion of lactate to glucose was examined in myotubes, minced muscle tissue, and rats exposed to 2H2O or 13C-enriched substrates. Myotubes or minced skeletal muscle incubated with [U-(13)C3]lactate released small amounts of [1,2,3-(13)C3]- or [4,5,6-(13)C3]glucose. This labeling pattern is consistent with direct transfer from lactate to glucose without randomization in the tricarboxylic acid (TCA) cycle. After exposure of incubated muscle to 2H2O, [U-(13)C3]lactate, glucose, and glutamine, there was minimal release of synthesized glucose to the medium based on a low level of 2H enrichment in medium glucose but 50- to 100-fold greater 2H enrichment in glucosyl units from glycogen. The 13C enrichment pattern in glycogen from incubated skeletal muscle was consistent only with direct transfer of lactate to glucose without exchange in TCA cycle intermediates. 13C nuclear magnetic resonance (NMR) spectra of glutamate from the same tissue showed flux from lactate through pyruvate dehydrogenase but not flux through pyruvate carboxylase into the TCA cycle. Carbon from an alternative substrate for glucose production that requires metabolism through the TCA cycle, propionate, did not enter glycogen, suggesting that TCA cycle intermediates do not exchange with phosphoenolpyruvate. In vivo, the 13C labeling patterns in hepatic glycogen and plasma glucose after administration of [U-(13)C3]lactate did not differ significantly. However, skeletal muscle glycogen was substantially enriched in [1,2,3-(13)C3]- and [4,5,6-(13)C3]glucose units that could only occur through skeletal muscle glyconeogenesis rather than glycogenesis. Lactate serves as a substrate for glyconeogenesis in vivo without exchange into symmetric intermediates of the TCA cycle.
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PMID:Evidence for reverse flux through pyruvate kinase in skeletal muscle. 1919 Feb 56

Pyruvate carboxylation (PC) is thought to be the major anaplerotic reaction for the tricarboxylic acid cycle and is necessary for de novo synthesis of amino acid neurotransmitters. In the brain, the main enzyme involved is pyruvate carboxylase, which is predominantly located in astrocytes. Carboxylation leads to the formation of oxaloacetate, which condenses with acetyl coenzyme A to form citrate. However, oxaloacetate may also be converted to malate and fumarate before being regenerated. This pathway is termed the oxaloacetate-fumarate-flux or backflux. Carbon isotope-based methods for quantification of activity of PC lead to underestimation when backflux is not taken into account and critical errors have been made in the interpretation of results from metabolic studies. This study was conducted to establish the degree of backflux after PC in cerebellar and neocortical astrocytes. Astrocyte cultures from cerebellum or neocortex were incubated with either [3-(13) C] or [2-(13) C]glucose, and extracts were analyzed using mass spectrometry or nuclear magnetic resonance spectroscopy. Substantial PC compared with pyruvate dehydrogenase activity was observed, and extensive backflux was demonstrated in both types of astrocytes. The extent of backflux varied between the metabolites, reaffirming that metabolism is highly compartmentalized. By applying our calculations to published data, we demonstrate the existence of backflux in vivo in cat, rat, mouse, and human brain. Thus, backflux should be taken into account when calculating the magnitude of PC to allow for a more precise evaluation of cerebral metabolism.
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PMID:Direct measurement of backflux between oxaloacetate and fumarate following pyruvate carboxylation. 2205 53