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:6.4.1.1 (pyruvate carboxylase)
1,516 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Treatment of 18 h-starved rats with dexamethasone and subsequent isolation and incubation of the hepatocytes in the presence of the steroid increased gluconeogenic flux with both 1.0 mM pyruvate and 1.0 mM lactate plus 0.2 mM pyruvate as the substrate. The magnitude of stimulation was comparable with both substrates. The increase in glucose output was accompanied by an increased flux through pyruvate carboxylase, although the absolute flux and magnitude were considerably less in the presence of the more reduced substrate. The effect of the steroid on the flux through pyruvate dehydrogenase was substrate-dependent, an inhibition occurring with the more oxidized substrate. There was no effect of steroid treatment on [1-14C]lactate or pyruvate oxidation or on tricarboxylic-acid-cycle flux as measured by [3-14C]pyruvate oxidation. Dexamethasone treatment resulted in a parallel increase in both pyruvate kinase flux and glucose synthesis with both substrates employed, indicating that the steroid had no effect on the partitioning of phosphoenolpyruvate between pyruvate and lactate formation and gluconeogenesis. Similarly there was no effect of the steroid on either the activity ratio or the total pyruvate kinase activity in the cells. It is suggested that the acute effect of the dexamethasone to increase gluconeogenesis resides at the level of phosphoenolpyruvate formation, i.e. pyruvate carboxylase and possibly phosphoenolpyruvate carboxykinase.
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PMID:Effect of dexamethasone on gluconeogenesis, pyruvate kinase, pyruvate carboxylase and pyruvate dehydrogenase flux in isolated hepatocytes. 843 80

Gluconeogenesis from isotopically substituted (3-13C)alanine (Ala) was demonstrated in the last larval instar of an insect, Manduca sexta, when maintained on low carbohydrate diets. 13C was incorporated into all carbons of the blood sugar trehalose (Tre), but enrichments of C1 and C6, and C2 and C5 were greatest. Relative to the amount of [3-13C]Ala metabolized, larvae maintained on a low carbohydrate diet supplemented with casein displayed the greatest enrichment of Tre. Very little de novo synthesis of Tre was observed in larvae maintained on a complete-balanced diet containing calorically equivalent amounts of sucrose and casein. Starvation failed to induce gluconeogenesis and 13C was not incorporated into Tre in starved insects. Activity of the TCA cycle contributed approximately 10% of the 13C incorporated into Tre in larvae on low carbohydrate diets, while the TCA cycle contribution in larvae on the complete diet approached 70%. The pattern of 13C enrichment of glucose in larvae on the low carbohydrate diets indicated that cytoplasmic carboxylation, possibly due to 'malic enzyme'-like activity, contributed significantly to the synthesis of Tre. The pentose phosphate pathway was evidenced in insects on all diets. Glucose labelling ratios indicated a pentose cycling flux of 10 to 20% in insects on the low carbohydrate diets and 50% in larvae on the complete diet. Glutamine together with lesser amounts of glutamate and glutathione were also products of the labelled Ala. The distribution of label in these products under different dietary conditions demonstrated shifts in the relative contribution of pyruvate carboxylase and pyruvate dehydrogenase activities for providing substrate to the TCA cycle. In the expected fashion starved insects and insects on the low carbohydrate diets incorporated a greater proportion of 13C into the TCA cycle via carboxylation while incorporation by the two pathways was similar in insects on the complete diet. The significance of these findings with regard to the regulation of gluconeogenesis in M. sexta and comparison of the present results with those obtained from studies of hepatic gluconeogenesis are discussed.
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PMID:Gluconeogenesis and effect of nutritional status on TCA cycle activity in the insect Manduca sexta. 854 15

Glucose and glutamine metabolism in several cultured mammalian cell lines (BHK, CHO, and hybridoma cell lines) were investigated by correlating specific utilization and formation rates with specific maximum activities of regulatory enzymes involved in glycolysis and glutaminolysis. Results were compared with data from two insect cell lines and primary liver cells. Flux distribution was measured in a representative mammalian (BHK) and an insect (Spodoptera frugiperda) cell line using radioactive substrates. A high degree of similarity in many aspects of glucose and glutamine metabolism was observed among the cultured mammalian cell lines examined. Specific glucose utilization rates were always close to specific hexokinase activities, indicating that formation of glucose-6-phosphate from glucose (catalyzed by hexokinase) is the rate limiting step of glycolysis. No activity of the key enzymes connecting glycolysis with the tricarboxylic acid cycle, such as pyruvate dehydrogenase, pyruvate carboxylase, and phosphoenolpyruvate carboxykinase, could be detected. Flux distribution in BHK cells showed glycolytic rates very similar to lactate formation rates. No glucose- or pyruvate-derived carbon entered the tricarboxylic acid cycle, indicating that glucose is mainly metabolized via glycolysis and lactate formation. About 8% of utilized glucose was metabolized via the pentose phosphate shunt, while 20 to 30% of utilized glucose followed pathways other than glycolysis, the tricarboxylic acid cycle, or the pentose phosphate shunt. About 18% of utilized glutamine was oxidized, consistent with the notion that glutamine is the major energy source for mammalian cell lines. Mammalian cells cultured in serum-free low-protein medium showed higher utilization rates, flux rates, and enzyme activities than the same cells cultured in serum-supplemented medium. Insect cells oxidized glucose and pyruvate in addition to glutamine. Furthermore, insect cells produced little or no lactate and were able to channel glycolytic intermediates into the tricarboxylic acid cycle. Metabolic profiles of the type presented here for a variety of cell lines may eventually enable one to interfere with the metabolic patterns of cells relevant to biotechnology, with the hope of improving growth rate and/or productivity.
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PMID:Comparative analysis of glucose and glutamine metabolism in transformed mammalian cell lines, insect and primary liver cells. 855 65

Isolated hepatocytes were prepared from the periportal and perivenous regions of the liver of 18-h-starved rats. These showed characteristics enzyme patterns and an enhanced rate of ureagenesis in the periportal cells; however, total cellular ATP content was unchanged in the two cell types. Measurements of pyruvate kinase flux showed no significant difference in the overall rate in the two cell types; however, the flux through phosphoenolpyruvate (PEP) carboxykinase was significantly higher in the periportal cells, such that the percentage of PEP being metabolized by pyruvate kinase was enhanced in the perivenous cells. The increase in partitioning of PEP through pyruvate kinase could account for only a small percentage of the difference in gluconeogenic flux in the two cell types, suggesting that the rate of provision of PEP was the principal limiting factor for glucose synthesis. The flux through pyruvate dehydrogenase showed no significant metabolic zonation, whereas pyruvate carboxylase flux was enhanced in the periportal zone. The partitioning of pyruvate between pyruvate carboxylase and pyruvate dehydrogenase was increase 2.8-fold in the periportal cells compared to that in the perivenous cells and it is suggested that this, together with possible alterations in phosphoenolpyruvate carboxykinase, is primarily responsible for the different gluconeogenic rates in the two zones of the liver.
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PMID:Measurement of metabolic fluxes through pyruvate kinase, phosphoenolpyruvate carboxykinase, pyruvate dehydrogenase, and pyruvate carboxylate in hepatocytes of different acinar origin. 861 Oct 24

A mathematical model of the citric acid cycle devoted to the analysis of 13C-NMR data was developed for determining the relative flux of molecules through the anaplerotic versus oxidative pathways and the relative pyruvate carboxylase versus pyruvate dehydrogenase activities. Different variants of the model were considered depending on the reversibility of the conversion of fumarate into malate and oxaloacetate. The model also included the possibility of orientation-conserved transfer of the four-carbon citric acid cycle intermediates, leading to conversion of succinyl-CoA C1 into either malate C1 or C4. It was used to analyse NMR data from glutamine isotopomers produced by cerebellar astrocytes incubated with [1-13C]glucose. Partial cycling (39%) between oxaloacetate and fumarate was evident from the analysis. Application of the model to glutamate isotopomers from granule cells incubated with [1-13C]glucose [Martin, M.. Portais, J.C.. Labouesse. J., Canioni. P, & Merle, M. (1993) Eur. J. Biochem. 217, 617-625] indicated that total cycling of oxaloacetate into fumarate was, in this case, required to get the best fit. The results emphasized some important differences in carbon metabolism between cerebellar astrocytes and granule cells concerning the sources of carbon fuelling the citric acid cycle and the carbon fluxes on different pathways.
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PMID:Mathematical modelling of the citric acid cycle for the analysis of glutamine isotopomers from cerebellar astrocytes incubated with [1(-13)C]glucose. 877 22

In rat hepatocytes exposed to [2-13C]pyruvate, newly formed glucose was more efficiently labeled in the carbon C5 than C2, as well as in the carbon C6 than C1, suggesting enzyme-to-enzyme channeling of D-glyceraldehyde 3-phosphate between glyceraldehyde-3-phosphate dehydrogenase and phosphofructoaldolase. Likewise the C1/C2 and C6/C5 ratios for 13C abundance in newly formed glucose, which largely exceeded the C3/C2 ratio of lactate or alanine and could reflect reversibility in the fumarase reaction, were compatible with the enzyme-to-enzyme tunneling of symmetrical Krebs cycle intermediates in the sequence of reactions catalyzed by succinyl-CoA synthetase, succinate dehydrogenase, and fumarase. This study further indicates that the major fraction of pyruvate is metabolized via pyruvate carboxylase rather than pyruvate dehydrogenase.
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PMID:D-glucose generation from [2-13C]pyruvate in rat hepatocytes: implications in terms of enzyme-to-enzyme channelling. 880 44

To gain insight into the regulation of pancreatic beta-cell mitochondrial metabolism, the direct effects on respiration of different mitochondrial substrates, variations in the ATP/ADP ratio and free Ca2+ were examined using isolated mitochondria and permeabilized clonal pancreatic beta-cells (HIT). Respiration from pyruvate was high and not influenced by Ca2+ in State 3 or under various redox states and fixed values of the ATP/ADP ratio; nevertheless, high Ca2+ elevated pyridine nucleotide fluorescence, indicating activation of pyruvate dehydrogenase by Ca2+. Furthermore, in the presence of pyruvate, elevated Ca2+ stimulated CO2 production from pyruvate, increased citrate production and efflux from the mitochondria and inhibited CO2 production from palmitate. The latter observation suggests that beta-cell fatty acid oxidation is not regulated exclusively by malonyl-CoA but also by the mitochondrial redox state. alpha-Glycerophosphate (alpha-GP) oxidation was Ca(2+)-dependent with a half-maximal rate observed at around 300 nM Ca2+. We have recently demonstrated that increases in respiration precede increases in Ca2+ in glucose-stimulated clonal pancreatic beta-cells (HIT), indicating that Ca2+ is not responsible for the initial stimulation of respiration [Civelek, Deeney, Kubik, Schultz, Tornheim and Corkey (1996) Biochem. J. 315, 1015-1019]. It is suggested that respiration is stimulated by increased substrate (alpha-GP and pyruvate) supply together with oscillatory increases in ADP [Nilsson, Schultz, Berggren, Corkey and Tornheim (1996) Biochem. J. 314, 91-94]. The rise in Ca2+, which in itself may not significantly increase net respiration, could have the important functions of (1) activating the alpha-GP shuttle, to maintain an oxidized cytosol and high glycolytic flux; (2) activating pyruvate dehydrogenase, and indirectly pyruvate carboxylase, to sustain production of citrate and hence the putative signal coupling factors, malonyl-CoA and acyl-CoA; and (3) increasing mitochondrial redox state to implement the switch from fatty acid to pyruvate oxidation.
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PMID:Regulation of pancreatic beta-cell mitochondrial metabolism: influence of Ca2+, substrate and ADP. 880 55

The most common defect associated with deficiency of the pyruvate dehydrogenase (PDH) complex occurs in the E1 component, specifically due to mutations in the X-linked E1 alpha gene. Clinical sequelae of these mutations, which range from severe neonatal lactic acidosis to carbohydrate-sensitive ataxia, can be different in males and females depending on the nature of the mutation and, in the case of females, on the X-inactivation pattern in different tissues. Males have a high representation of missense mutations among the patient cohort, while females are much more likely to have DNA rearrangements, particularly toward the 3' end of the coding sequence of the gene. Missplicing mutations involving exon 6 deletion have been reported, as has a missense mutation conferring true thiamin-responsiveness of the enzyme and the patient's clinical symptoms. Pyruvate carboxylase deficiency, on the other hand, is a true autosomal recessive disease, though it has high occurrences in particular ethnic groups, especially in Algonkian-speaking Amerindians and in Arabs. In the former group the defect is a simple type in which material cross-reactive to pyruvate carboxylase antibody is present in cultured cells (CRM+ve). In the latter group, cross-reacting material is rarely present (CRM-ve). The CRM+ve patients can survive into teenage years with careful supervision, while the CRM-ve patients have complications due to hyperammonaemia and dysfunction of the urea cycle and rarely survive beyond 3 months of life.
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PMID:Disorders of pyruvate carboxylase and the pyruvate dehydrogenase complex. 888 69

A number of acquired conditions including infections, severe catabolic states, tissue anoxia, severe dehydration and poisoning can give rise to hyperlactacidaemia. All these causes should be ruled out before considering inborn errors of metabolism. Carefully collected samples are necessary if artefacts that result in spuriously increased lactate/pyruvate (L/P) and 3-hydroxybutyrate/acetoacetate (B/A) ratios are to be avoided. When properly performed, 24-h studies of L/P and B/A ratios provide a useful tool in making a diagnosis. A few metabolic profiles when present are specific or highly suggestive of a given disorder. When the L/P ratio is normal or low, pyruvate dehydrogenase (PDH) deficiency is highly probable whatever the lactate concentration, which is often only moderately elevated after meal, may be. When the L/P ratio is very high in association with post-prandial hyperketonaemia and in contrast to a normal or low B/A ratio, pyruvate carboxylase (PC) deficiency and alpha-ketoglutarate dehydrogenase (KGDH) deficiency are the most likely diagnoses. The distinction between the two disorders relies upon amino acid and organic acid profiles (glutamate and alpha-ketoglutarate accumulations in KGDH deficiency and hyperammonaemia and hypercitrullinaemia in PC deficiency). When both L/P and B/A ratios are elevated and associated with significant post-prandial hyperketonaemia, respiratory-chain disorders should first be suspected. All other profiles, especially a high L/P ratio without hyperketonaemia, are compatible with respiratory-chain disorders but are not specific; all acquired anoxic conditions should also be ruled out. Clearly, the clinical utility of these profiles needs to be interpreted cautiously in very ill patients in relation to the cardiocirculatory condition and to therapy. Finally, a normal profile, even after stress and loading, does not rule out an inborn error of lactate/pyruvate oxidation.
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PMID:Metabolic intermediates in lactic acidosis: compounds, samples and interpretation. 888 72

We analyzed the glutamine isotopomers released into the extracellular medium by cerebellar astrocytes incubated with [1-13C]glucose. We developed a mathematical model of the tricarboxylic acid (TCA) cycle to determine the relative flux of molecules through the anaplerotic versus oxidative pathways and the relative pyruvate carboxylase versus pyruvate dehydrogenase activities. As glutamine C2 and C3 exhibited unequivalent enrichments, we examined the possibility of: (1) both the entry of the label into the TCA cycle from pyruvate and the conversion of the oxaloacetate into citrate before equilibration with fumarate, and (2) the occurrence of an orientation-conserved transfer of the symmetrical 4-carbon intermediates. The best fit required partial cycling between oxaloacetate and fumarate, whereas the occurrence of any orientation-conserved transfer was rejected. On the other hand, the analysis of glutamate isotopomers from perchloric acid extracts of granule cells incubated with [1-13C]glucose indicated that total cycling of oxaloacetate into fumarate occurred in these cells.
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PMID:[1-13C]glucose metabolism in brain cells: isotopomer analysis of glutamine from cerebellar astrocytes and glutamate from granule cells. 894 Jun 19


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