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 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

The activities of various ammoniagenic, gluconeogenic, and glycolytic enzymes were measured in the renal cortex and also in the liver of rats made diabetic with streptozotocin. Five groups of animals were studied: normal, normoglycemic diabetic (insulin therapy), hyperglycemic, ketoacidotic, and ammonium chloride treated rats. Glutaminase I, glutamate dehydrogenase, glutamine synthetase, phosphoenolpyruvate carboxykinase (PEPCK), hexokinase, phosphofructokinase, fructose-1,6-diphosphatase, malate dehydrogenase, malic enzyme, and lactate dehydrogenase were measured. Renal glutaminase I activity rose during ketoacidosis and ammonium chloride acidosis. Glutamate dehydrogenase in the kidney rose only in ammonium chloride treated animals. Glutamine synthetase showed no particular variation. PEPCK rose in diabetic hyperglycemic animals and more so during ketoacidosis and ammonium chloride acidosis. It also rose in the liver of the diabetic animals. Hexokinase activity in the kidney rose in diabetic insulin-treated normoglycemic rats and also during ketoacidosis. The same pattern was observed in the liver of these diabetic rats. Renal and hepatic phosphofructokinase activities were elevated in all groups of experimental animals. Fructose-1,6-diphosphatase and malate dehydrogenase did not vary significantly in the kidney and the liver. Malic enzyme was lower in the kidney and liver of the hyperglycemic diabetic animals and also in the liver of the ketoacidotic rats. Lactate dehydrogenase fell slightly in the liver of diabetic hyperglycemic and NH4Cl acidotic animals. The present study indicates that glutaminase I is associated with the first step of increased renal ammoniagenesis during ketoacidosis. PEPCK activity is influenced both by hyperglycemia and ketoacidosis, acidosis playing an additional role. Insulin appears to prevent renal gluconeogenesis and to favour glycolysis. The latter would seem to remain operative in hyperglycemic and ketoacidotic diabetic animals.
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PMID:Renal enzymes during experimental diabetes mellitus in the rat. Role of insulin, carbohydrate metabolism, and ketoacidosis. 623 75

Renal adaptation to chronic metabolic acidosis was studies in Arbor Acre hens receiving ammonium chloride by stomach tube 0.75 g/kg/day during 6 days. During a 14-day study, it was shown that the animals could excrete as much as 60% of the acid load during ammonium chloride administration. At the same time urate excretion fell markedly but the renal contribution to urate excretion (14%) did not change. During acidosis, blood glutamine increased twofold and the tissue concentration of glutamine rose in both liver and kidney. Infusion of L-glutamine led to increased ammonia excretion and more so in acidotic animals. Glutaminase I, glutamate dehydrogenase, alanine aminotransferase (GPT), and malic enzyme activities increased in the kidney during acidosis but phosphoenolpyruvate carboxykinase (PEPCK) activity did not change. Glutaminase I was not found in the liver, but hepatic glutamine synthetase rose markedly during acidosis. Glutamine synthetase was not found in the kidney. Renal tubules incubated with glutamine and alanine were ammoniagenic and gluconeogenic to the same degree as rat tubules with the same increments in acidosis. Lactate was gluconeogenic without increment during acidosis. The present study indicates that the avian kidney adapts to chronic metabolic acidosis with similarities and differences when compared to dog and rat. Glutamine originating from the liver appears to be the major ammoniagenic substrate. Our data also support the hypothesis that hepatic urate synthesis is decreased during acidosis.
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PMID:The kidney of chicken adapts to chronic metabolic acidosis: in vivo and in vitro studies. 681 56

The effect of anisoosmolarity on the abundance of various mRNA species was examined in perfused rat liver and H4IIE rat hepatoma cells. Hyperosmotic exposure (385 mosmol/l) of isolated rat livers increased mRNA levels for tyrosine aminotransferase (TAT) by 246% and those for phosphoenolpyruvate carboxykinase (PEPCK) by 186%, whereas hypoosmotic exposure (225 mosmol/l) decreased their levels to 43% and 42%, respectively. mRNA levels for fructose-1,6-bisphosphatase (FBP), argininosuccinate lyase (ASL), argininosuccinate synthetase (ASS), glutamine synthetase (GS), glutaminase (GA) and glucokinase (GK) were largely unaffected. In H4IIE cells the modulation of TAT and PEPCK mRNA levels by anisoosmotic exposure was similar to that found in perfused rat liver. ASL and glutaminase mRNA levels were influenced in an opposite manner. The effects of anisoosmolarity on PEPCK mRNA levels in H4IIE cells were largely abolished in the presence of the protein kinase inhibitors H-7, H-89 and HA-1004. Other protein kinase inhibitors such as Go-6850, KN-62, Rp-8-CPT-cAMPS, rapamycin, wortmannin, genistein or herbimycin did not prevent the osmosensitivity of PEPCK mRNA levels. Also pertussis and cholera toxin, vanadate and colchicine did not affect the osmosensitivity of PEPCK mRNA levels. The data suggest that anisoosmotic exposure acts on the levels of some but not all mRNA species and that this action may involve changes in protein phosphorylation. They further indicate that the recently identified osmosensitive signal transduction pathway which involves a G-protein and tyrosine kinase dependent activation of mitogen-activated protein kinases is apparently not involved in the osmoregulation of PEPCK mRNA levels.
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PMID:Anisoosmotic regulation of hepatic gene expression. 892 14

The rabbit kidney does not readily metabolize but synthesizes glutamine at high rates by pathways that remain poorly defined. Therefore, the metabolism of variously labeled [13C]- and [14C]glutamates has been studied in isolated rabbit kidney tubules with and without acetate. CO2, glutamine, and alanine were the main carbon and nitrogenous end products of glutamate metabolism but no ammonia accumulated. Absolute fluxes through enzymes involved in glutamate metabolism, including enzymes of four different cycles operating simultaneously, were assessed by combining mainly the 13C NMR data with a new model of glutamate metabolism. In contrast to a previous conclusion of Klahr et al. (Klahr, S., Schoolwerth, A. C., and Bourgoignie, J. J. (1972) Am. J. Physiol. 222, 813-820), glutamate metabolism was found to be initiated by glutamate dehydrogenase at high rates. Glutamate dehydrogenase also operated at high rates in the reverse direction; this, together with the operation of the glutamine synthetase reaction, masked the release of ammonia. Addition of acetate stimulated the operation of the "glutamate --> alpha-ketoglutarate --> glutamate" cycle and the accumulation of glucose but reduced both the net oxidative deamination of glutamate and glutamine synthesis. Acetate considerably increased flux through alpha-ketoglutarate dehydrogenase and citrate synthase at the expense of flux through phosphoenolpyruvate carboxykinase; acetate also caused a large decrease in flux through alanine aminotransferase, pyruvate dehydrogenase, and the "substrate cycle" involving oxaloacetate, phosphoenolpyruvate, and pyruvate.
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PMID:The rabbit kidney tubule simultaneously degrades and synthesizes glutamate. A 13C NMR study. 903 May 22

Sea raven (Hemitripterus americanus) given intraperitoneal implants of coconut oil containing cortisol (50 mg kg-1) and sampled 5 days later had plasma cortisol, glucose and urea concentrations higher than in a sham-implanted group. No differences in plasma ammonia, free amino acid or fatty acid concentrations were apparent between the cortisol- and sham-treated groups. There was no change in hepatic glycogen content, whereas glutamine synthetase, allantoicase, arginase, aspartate aminotransferase, tyrosine aminotransferase, alanine aminotransferase, glutamate dehydrogenase, phosphoenolpyruvate carboxykinase and 3-hydroxyacyl-coenzyme A dehydrogenase activities were higher in the cortisol-treated fish liver compared with the sham-implanted fish. On the basis of these general increases in enzyme activities, our results suggest that cortisol stimulates nitrogen metabolism in the sea raven. Amino acid catabolism may be a major source of substrate for gluconeogenesis and/or oxidation, while fatty acid mobilization may provide the fuel for endogenous use by the liver in cortisol-treated sea raven. These results further support the hypothesis that cortisol plays a role in the regulation of glucose production in stressed fish.
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PMID:Metabolic effects of cortisol treatment in a marine teleost, the sea raven 931 10

We have isolated a conditionally transformed liver progenitor cell line with phenotypic similarities to both hepatoblasts (bipotent embryonic liver cells that give rise to hepatocytes and intrahepatic biliary epithelial cells) and liver epithelial cells (primitive hepatic cells isolated from adult livers capable of generating both hepatocytic and biliary lineages). Cell line L2039 was derived from E14 fetal mouse liver after transformation with temperature-sensitive SV-40 large T antigen. At 33 degrees C, these cells have an epithelial morphology with a high nucleocytoplasmic ratio and express both hepatocytic and biliary genes, including albumin, alpha-fetoprotein, glutamine synthetase, insulinlike growth factor II receptor, fibronectin and laminin, and cytokeratins 8 and 19, a set of markers characteristic for hepatoblasts. The presence of cytokeratin 14, vimentin, and several oval-cell antigens link cell line L2039 to nonparenchymal liver epithelial cell populations thought to contain progenitor cells. Serum-free, hormonally defined media conditions and extracellular matrix requirements were determined for growth and differentiation of this cell line. During culture on type IV collagen at 39 degrees C, L2039 cells cease dividing and demonstrate hepatocytic differentiation with the assumption of a hepatocytelike morphology and glucocorticoid-dependent regulation of liver-specific genes, including albumin, alpha-fetoprotein, phosphoenolpyruvate carboxykinase, and liver-enriched transcription factors. The number of albumin-positive cells increases during culture at 39 degrees C, indicating that L2039 cells convert from a prehepatocytic to a hepatocytic phenotype. Under conditions specific for hepatocytic differentiation, C/EBPs were expressed and differentially regulated, with C/EBPbeta and C/EBPdelta upregulated early and C/EBPalpha only slightly expressed after 7 d, indicating that C/EBPalpha may not be a crucial factor in commitment to the hepatocytic phenotype.
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PMID:Maturation-dependent gene expression in a conditionally transformed liver progenitor cell line. 955 43

Unlike other lactic acid bacteria, Lactococcus lactis subsp. lactis NCDO 2118 was able to grow in a medium lacking glutamate and the amino acids of the glutamate family. Growth in such a medium proceeded after a lag phase of about 2 days and with a reduced growth rate (0.11 h-1) compared to that in the reference medium containing glutamate (0.16 h-1). The enzymatic studies showed that a phosphoenolpyruvate carboxylase activity was present, while the malic enzyme and the enzymes of the glyoxylic shunt were not detected. As in most anaerobic bacteria, no alpha-ketoglutarate dehydrogenase activity could be detected, and the citric acid cycle was restricted to a reductive pathway leading to succinate formation and an oxidative branch enabling the synthesis of alpha-ketoglutarate. The metabolic bottleneck responsible for the limited growth rate was located in this latter pathway. As regards the synthesis of glutamate from alpha-ketoglutarate, no glutamate dehydrogenase was detected. While the glutamate synthase-glutamine synthetase system was detected at a low level, high transaminase activity was measured. The conversion of alpha-ketoglutarate to glutamate by the transaminase, the reverse of the normal physiological direction, operated with different amino acids as nitrogen donor. All of the enzymes assayed were shown to be constitutive.
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PMID:Glutamate Biosynthesis in Lactococcus lactis subsp. lactis NCDO 2118 964 19

In the liver, genes are expressed along a portocentral gradient. Based on their adaptive behavior, a gradient versus compartment type, and a dynamic versus stable type of gradient have been recognized. To understand at least in principle the development and maintenance of these gradients in gene expression in relation to the limited number of signal gradients, we propose a simple and testable model. The model uses portocentral gradients of signal molecules as input, while the output depends on two gene-specific variables, viz., the affinity of the gene for its regulatory factors and the degree of cooperativity that determines the response in the signal-transduction pathways. As a preliminary validity test for its performance, the model was tested on control and hormonally induced expression patterns of phosphoenolpyruvate carboxykinase (PCK), carbamoylphosphate synthetase I (CPS), and glutamine synthetase (GS). Affinity was found to determine the overall steepness of the gradient, whereas cooperativity causes these gradients to steepen locally, as is necessary for a compartment-like expression pattern. Interaction between two or more different signal gradients is necessary to ensure a stable expression pattern under different conditions. The diversity in sequence and arrangement of related DNA-response elements of genes appears to account for the gene-specific shape of the portocentral gradients in expression. The feasibility of testing the function of hepatocyte-specific DNA-response units in vivo is demonstrated by integrating such units into a ubiquitously active promoter/enhancer and analyzing the pattern of expression of these constructs in transgenic mice.
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PMID:A mechanistic model for the development and maintenance of portocentral gradients in gene expression in the liver. 1009 63

Legumes obtain a substantial portion of their nitrogen (N) from symbiotic N2 fixation in root nodules. The glutamine synthetase (GS, EC 6.3.1.2)/glutamate synthase (GOGAT) cycle is responsible for the initial N assimilation. This report describes the analysis of a transgenic alfalfa (Medicago sativa L.) line containing an antisense NADH-GOGAT (EC 1.4.1.14) under the control of the nodule-enhanced aspartate amino-transferase (AAT-2) promoter. In one transgenic line, NADH-GOGAT enzyme activity was reduced to approximately 50%, with a corresponding reduction in protein and mRNA. The transcript abundance for cytosolic GS, ferredoxin-dependent GOGAT (EC 1.4.7.1), AAT-2 (EC 2.6.1.1), asparagine synthase (EC 6.3.5.4), and phosphoenolpyruvate carboxylase (PEPC, EC 4.1.1.31) were unaffected, as were enzyme activities for AAT, PEPC and GS. Antisense NADH-GOGAT plants grown under symbiotic conditions were moderately chlorotic and reduced in growth and N content, even though symbiotic N2 fixation was not significantly reduced. The addition of nitrate relieved the chlorosis and restored growth and N content. Surprisingly, the antisense NADH-GOGAT plants were male sterile resulting from inviable pollen. A reduction in NADH-GOGAT enzyme activity and transcript abundance in the antisense plants was measured during the early stages of flower development. Inheritance of the transgene was stable and resulted in progeny with a range of NADH-GOGAT activity. These data indicate that NADH-GOGAT plays a critical role in the assimilation of symbiotically fixed N and during pollen development.
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PMID:Decreased NADH glutamate synthase activity in nodules and flowers of alfalfa (Medicago sativa L.) transformed with an antisense glutamate synthase transgene. 1093 93


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