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)

Mitochondrial damage may be a major cause of cellular aging. So far, this hypothesis had only been tested using isolated mitochondria. The aim of this study was to investigate the involvement of mitochondria in aging using whole liver cells and not isolated mitochondria only. Using flow cytometry, we found that age is associated with a decrease in mitochondrial membrane potential (30%), an increase in mitochondrial size, and an increase in mitochondrial peroxide generation (23%). Intracellular peroxide levels were also increased. The number of mitochondria per cell and inner mitochondrial membrane mass did not change. Gluconeogenesis from glycerol or fructose (mitochondrial-independent) did not change with age, whereas it did from lactate (mitochondrial-dependent). The change in the rate of gluconeogenesis was not accompanied by changes in any of the following parameters: phosphoenolpyruvate carboxykinase or pyruvate carboxylase activities or mitochondrial ATP/ADP or cytosolic NADH/NAD+ ratios. This was caused by a decreased rate of malate export (to 20% of the controls) from mitochondria. The impairment of the mitochondrial malate transporter is posttranscriptional because its expression in Xenopus oocytes using polyadenylated RNA from livers of young or old animals did not change. Ketogenesis from oleate also fell in hepatocytes from old rats. Our results show, for the first time in intact cells, a correlation between age-associated impairment of cell metabolism and specific changes in mitochondrial function and morphology, supporting the hypothesis that mitochondrial damage plays a key role in aging.
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PMID:Aging of the liver: age-associated mitochondrial damage in intact hepatocytes. 890 98

We have cloned and characterized a gene encoding pyruvate carboxylase from the methylotrophic yeast Pichia pastoris. Disruption of this gene produced inability to grow in minimal medium with glucose as carbon source and ammonium as nitrogen source. Growth was possible with aspartate or glutamate as nitrogen source. The gene PpPYC1 expressed from its own promoter was able to rescue the phenotype of Saccharomyces cerevisiae mutants devoid of pyruvate carboxylase. In a P. pastoris strain carrying a disrupted PpPYC1 gene we have isolated spontaneous mutants able to grow in non-permissive conditions. In a mutant strain grown in glucose several enzymes sensitive to catabolite repression were derepressed. The strain also had elevated levels of glutamate dehydrogenase (NAD) both in repressed and derepressed conditions.
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PMID:Isolation of the Pichia pastoris PYC1 gene encoding pyruvate carboxylase and identification of a suppressor of the pyc phenotype. 963 11

The hypothesis proposing that anaplerosis and cataplerosis play an important role in fuel signaling by providing mitochondrially derived coupling factors for stimulation of insulin secretion was tested. A rise in citrate coincided with the initiation of insulin secretion in response to glucose in INS-1 beta-cells. The dose dependence of glucose-stimulated insulin release correlated closely with those of the cellular contents of citrate, malate, and citrate-derived malonyl-CoA. The glucose-induced elevations in citrate, alpha-ketoglutarate, malonyl-CoA, and the 3-[4,5-dimethylthiazol-2yl]-2,5-diphenyltetrazolium reduction state, an index of beta-cell metabolic activity, were unaffected by the Ca2+ chelator EGTA. Glucose induced a rise in both mitochondrial and cytosolic citrate and promoted efflux of citrate from the cells. The latter amounted to approximately 20% of glucose carbons entering the glycolytic pathway. Phenylacetic acid, a pyruvate carboxylase inhibitor, reduced the glucose-induced rise in citrate in INS-1 cells and insulin secretion in both INS-1 cells and rat islets. The results indicate the feasibility of a pyruvate/citrate shuttle in INS-1 beta-cells, allowing the regeneration of NAD+ in the cytosol and the formation of cytosolic acetyl-CoA, malonyl-CoA, and NADPH. The data suggest that anaplerosis and cataplerosis are early signaling events in beta-cell activation that do not require a rise in Ca2+. It is proposed that citrate is a signal of fuel abundance that contributes to beta-cell activation in both the mitochondrial and cytosolic compartments and that a major fate of anaplerotic glucose carbons is external citrate.
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PMID:Glucose-regulated anaplerosis and cataplerosis in pancreatic beta-cells: possible implication of a pyruvate/citrate shuttle in insulin secretion. 1090 79

The biochemical events associated with the onset of lipid accumulation in Mucor circinelloides and Mortierella alpina, under conditions of nitrogen-limited growth, have been elucidated; they differ in key aspects from those described in oleaginous yeasts. The NAD+:isocitrate dehydrogenases of Mc. circinelloides and Mort. alpina were not absolutely dependent on AMP for activity. Furthermore, changes in the cellular adenine nucleotide pools and energy charge were different from those reported for oleaginous yeasts. In Mc. circinelloides ATP, ADP and AMP concentrations all decreased by 50% after nitrogen limitation, leading to a constant energy charge at the expense of the size of the total adenylate pool. Pyruvate carboxylase in Mc. circinelloides was cytosolic, having implications for the organization of lipid synthesis in filamentous fungi. As a result of the data obtained, a revised and more concerted mechanism for the initiation of storage lipid accumulation is put forward for filamentous fungi.
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PMID:Biochemical events leading to the diversion of carbon into storage lipids in the oleaginous fungi Mucor circinelloides and Mortierella alpina. 1157 64

Enzymatic activities of ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) (EC 4.1.1.39), phospho(enol)pyruvate carboxylase (EC 4.1.1.31), NAD malate dehydrogenase (EC 1.1.1.37), and NADP glyceraldehydephosphate dehydrogenase complex including phosphoglycerate kinase (EC 2.7.2.3) and glyceraldehydephosphate dehydrogenase (EC 1.2.1.13) were comparatively assayed in wheat seedlings of the cultivar Lyutestsens 758 grown under normal conditions, water deficiency conditions, and subsequent rehydration. Water stress was found to decrease the activity of all enzymes tested, the effect being most pronounced in case of Rubisco. The content of Rubisco in wheat plants exposed to water deficiency was reduced less significantly than the activity of the enzyme. Preliminary treatment of plant seeds with kartolin-4 (o-isopropyl-N-2-hydroxyethyl carbamate), a preparation with cytokinin activity, reduced the dehydration-induced inhibition of enzymatic activity. Upon a subsequent rehydration, kartolin-4 facilitated rapid recovery of the photosynthetic activity, the process being based on the kartolin-induced stimulation of reparation reactions. Under conditions of water stress, a partial decrease in the activity of carbon metabolism enzymes in vitro was accompanied by complete inhibition of photosynthesis in vivo, perhaps, as a result of an abrupt increase in the stomatal resistance.
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PMID:[Activity of carbon metabolism enzymes in wheat plants treated with kartolin-4 and exposed to water stress]. 1177 26

Long-term exposure of the pancreatic beta cells to free fatty acid (FFA) reportedly inhibits glucose-stimulated insulin secretion. We here studied the impact of FFA on glucose and lipid metabolism in pancreatic beta cells with special reference to insulin secretion. Pancreatic beta-cell line MIN6 was exposed to various concentrations of palmitate for 3 days. Glucose-stimulated insulin secretion and insulin content were decreased corresponding to the concentration of the palmitate exposed. Glycolytic flux and ATP synthesis was unchanged, but pyruvate-stimulated change in NAD(P)H concentration was decreased. Pyruvate carboxylase was decreased at the protein level, which was restored by the removal of palmitate or the inhibition of beta-oxidation. Intracellular content of triglyceride and FFA were elevated, beta-oxidation was increased, and de novo lipogenesis from glucose was decreased. NADPH content and citrate output into the medium, which reflected pyruvate malate shuttle flux, were decreased, but malic enzyme activity was unaffected. The malic enzyme inhibitor alone inhibited insulin response to glucose. In conclusion, long-term exposure of FFA to beta cells inhibits glucose-stimulated insulin secretion via the decreased NADPH contents due to the inhibition of pyruvate carboxylase and malate pyruvate shuttle flux.
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PMID:Metabolic consequence of long-term exposure of pancreatic beta cells to free fatty acid with special reference to glucose insensitivity. 1178 Nov 46

The effects of benfluorex and two of its metabolites (S 422-1 and S 1475-1) on fatty acid and glucose metabolic fluxes and specific gene expression were studied in hepatocytes isolated from 24-h fasted rats. Both benfluorex and S 422-1 (0.1 or 1 mmol/l) reduced beta-oxidation rates and ketogenesis, whereas S 1475-1 had no effect. At the same concentration, benfluorex and S 422-1 were more efficient in reducing gluconeogenesis from lactate/pyruvate than S 1475-1. Benfluorex inhibited gluconeogenesis at the level of pyruvate carboxylase (45% fall in acetyl-CoA concentration) and of glyceraldehyde-3-phosphate dehydrogenase (decrease in ATP/ADP and NAD(+)/NADH ratios). Accordingly, neither benfluorex nor S 422-1 inhibited gluconeogenesis from dihydroxyacetone, but both stimulated gluconeogenesis from glycerol. In hepatocytes cultured in the presence of benfluorex or S 422-1 (10 or 100 micromol/l), the expression of genes encoding enzymes of fatty acid oxidation (carnitine palmitoyltransferase [CPT] I), ketogenesis (hydroxymethylglutaryl-CoA synthase), and gluconeogenesis (glucose-6-phosphatase, PEPCK) was decreased, whereas mRNAs encoding glucokinase and pyruvate kinase were increased. By contrast, Glut-2, acyl-CoA synthetase, and CPT II gene expression was not affected by benfluorex or S 422-1. In conclusion, this work suggests that benfluorex mainly via S 422-1 reduces gluconeogenesis by affecting gene expression and metabolic status of hepatocytes.
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PMID:Effects of benfluorex on fatty acid and glucose metabolism in isolated rat hepatocytes: from metabolic fluxes to gene expression. 1214 46

Fatty acid synthesis via the citrate cleavage pathway requires the continual replenishment of oxaloacetate within the mitochondria, probably by carboxylation of pyruvate. Malic enzyme, although present in adipose tissue, is completely localized in the cytoplasm and has insufficient activity to support lipogenesis. Pyruvate carboxylase was found to be active in both the mitochondria and cytoplasm of epididymal adipose tissue cells; it was dependent on both ATP and biotin. Alteractions in dietary conditions induced no significant changes in mitochondrial pyruvate carboxylase activity, but the soluble activity was depressed in fat-fed animals. The possible importance of the soluble activity in lipogenesis lies in its participation in a soluble malate transhydrogenation cycle with NAD malate dehydrogenase and malic enzyme, whereby a continual supply of NADPH is produced. Consequently, the pyruvate carboxylase in adipose tissue both generates mitochondrial oxaloacetate for the citrate cleavage pathway and supplies soluble NADPH for the conversion of acetyl-CoA to fatty acid.
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PMID:The citrate cleavage pathway and lipogenesis in rat adipose tissue: replenishment of oxaloacetate. 1456 11

Krebs cycle enzyme activities and levels of five metabolites were determined from livers of old mice (30 months) maintained either on control or on long-term caloric restriction (CR) diets (28 months). In CR mice, the cycle was divided into two major blocks, the first containing citrate synthase, aconitase and NAD-dependent isocitrate dehydrogenase which showed decreased activities, while the second block, containing the remaining enzymes, displayed increased activity (except for fumarase, which was unchanged). CR also resulted in decreased levels of citrate, glutamate and alpha-ketoglutarate, increased levels of malate, and unchanged levels of aspartate. The alpha-ketoglutarate/glutamate and malate/alpha-ketoglutarate ratios were higher in CR, in parallel with previously reported increases with CR in pyruvate carboxylase activity and glucagon levels, respectively. The results indicate that long-term CR induces a differential regulation of Krebs cycle in old mice and this regulation may be the result of changes in gene expression levels, as well as a complex interplay between enzymes, hormones and other effectors. Truncation of Krebs cycle by CR may be an important adaptation to utilize available substrates for the gluconeogenesis necessary to sustain glycolytic tissues, such as brain.
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PMID:Krebs cycle enzymes from livers of old mice are differentially regulated by caloric restriction. 1528 89

Lactate and succinate were produced from glucose by Corynebacterium glutamicum under oxygen deprivation conditions without growth. Addition of bicarbonate to the reaction mixture led not only to a 3.6-fold increase in succinate production rate, but also to a 2.3- and 2.5-fold increase, respectively, of the rates of lactate production and glucose consumption, compared to the control. Furthermore, when small amounts of pyruvate were added to the reaction mixture, acid production rates and the glucose consumption rate were multiplied by a factor ranging from 2 to 3. These phenomena were paralleled by an increase in the NAD(+)/NADH ratio, thus corroborating the view that the efficient regeneration of NAD(+) could be triggered by the addition of either bicarbonate or pyruvate. To investigate the global metabolism of corynebacteria under oxygen deprivation conditions, we engineered several strains where the genes coding for key metabolic enzymes had been inactivated by gene disruption and replacement. A lactate dehydrogenase (LDH)-deficient mutant was not able to produce lactate, suggesting this enzyme has no other isozyme. Although a pyruvate carboxylase (pyc) mutant exhibited similar behavior to that of the wild type, phosphoenolpyruvate carboxylase (ppc) mutants were characterized by a dramatic decrease in succinate production, which was concomitant to decreased lactate production and glucose consumption rates. This set of observations corroborates the view that in coryneform bacteria under oxygen deprivation conditions the major anaplerotic reaction is driven by the ppc gene product rather than by the pyc gene product. Moreover, intracellular NADH concentrations in C. glutamicum were observed to correlate to oxygen-deprived metabolic flows.
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PMID:Metabolic analysis of Corynebacterium glutamicum during lactate and succinate productions under oxygen deprivation conditions. 1538 16


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