Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: EC:4.1.1.49 (phosphoenolpyruvate carboxykinase)
4,654 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

We review the development of our knowledge and interpretations of the intermediary metabolism of Trypanosoma (Schizotrypanum) cruzi. Already in the 1950's it was clearly established that when this organism was exposed to large external concentrations of carbohydrates it was unable to catabolize them completely, even in the presence of oxygen, producing a mixture of CO2, dicarboxylic acids (succinic, malic) and alanine as end products. However, subsequent work tended to emphasize such paradigmatic features as a full complement of glycolytic enzymes in all stages of the life cycle of the parasite, a functional Kreb's cycle, a cytochrome-dependent electron transport chain and phosphorylative oxidation which suggested that T. cruzi had the basic metabolic properties of classical glucose-utilizing cells, in contrast with the degenerate glycolytic metabolism of bloodstream African trypanosomes. Only in the 1980's interest revived on the how and why of the incomplete carbohydrate catabolism by this parasite. The primary reason for this anomaly was found to be the presence of a constitutive phospho-enol-pyruvate carboxykinase (PEPCK, ATP-dependent, E.C.4.1.1.49), present in all stages of the parasite's life cycle, and the lack of regulation of the glycolytic route at its classical control points, hexokinase and phosphofructokinase. On the other hand, the presence of two distinct glutamate dehydrogenases (NAD+ and NADP(+)-dependent), the former being strictly regulated by the energy charge of the cell and the Krebs' cycle activity, indicated that amino acids can be a primary source of energy for this organism.(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:The limitations of paradigms: studies on the intermediary metabolism of Trypanosoma cruzi. 767 May 50

Estradiol treatment of starving immature rainbow trout dramatically alters the metabolic performance of isolated hepatocytes. One and two weeks postimplantation with estradiol, the rate of de novo glucose synthesis from [14C]alanine is reduced fourfold from 0.4 mumol/g/hr to 0.1 mumol/g/hr, compared with vehicle-injected control fish. After 6 weeks, the rate of glucose production on a gram wet weight basis is identical in both treatment groups, but significantly larger (by 80%) in the estradiol-treated group than in the controls, if expressed normalized to the hepatosomatic index (HSI). Estradiol treatment caused preferential partitioning of alanine carbon into oxidative pathways away from gluconeogenesis, indicated by a significantly lower ratio of glucose production over CO2 production in hepatocytes isolated from estradiol-treated animals. Incorporation of [14C]alanine into acid-precipitable protein is significantly larger in the estradiol-treated group after 2 weeks, and also after 6 weeks, when normalized to the HSI, indicating that part of the protein synthesized in the estradiol-treated groups is vitellogenin. No differences were detected between estradiol-treated animals and control animals in the activities of enzymes associated with gluconeogenesis [phosphoenolpyruvate carboxykinase, fructose 1,6-bisphosphatase (FBPase)] and amino acid metabolism (alanine and aspartate aminotransferases) in the time course investigated (expressed on a wet weight basis). Activities normalized to the HSI are higher in fish implanted with estradiol compared with controls at 2 and 6 weeks. In keeping with the increased potential of hepatocytes for CO2 production from alanine, estradiol treatment doubled and tripled the maximum activity of pyruvate kinase 1 and 2 weeks postimplantation, respectively. Fish were fasted to avoid erratic feeding due to treatments. Superimposed on estradiol actions are effects of starvation: a fourfold increase in the rate of gluconeogenesis, a threefold increase in oxidative flux, and a fivefold increase in the activity of FBPase--all normalized to hepatocyte weight.
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PMID:Gluconeogenesis in hepatocytes of immature rainbow trout (Oncorhynchus mykiss): control by estradiol. 767 84

The results from the experiments performed with a mutant deficient in citrate synthase activity can be summarized as follows. (1) Totally blocking entry into the TCA cycle did not appreciably alter the cellular ATP yield. The unchanged yield suggests that for growth on abundant glucose, the sensitivity of ATP yield to TCA cycle flux is low. ATP production in the mutant is altered, in part, by modulating the relative amounts of formate and acetate produced. (2) The in vivo operation of pyruvate-formate lyase and malic enzyme corresponds to proposals developed from in vitro studies. Namely, pyruvate activates the former, and acetyl CoA inhibits the latter. Overall, the diversion of pyruvate to formate under aerobic conditions constitutes an adaptation of the mutant to the enzymatic lesion. The low alpha-ketoglutarate dehydrogenase flux estimated for the mutant indicates that the enzyme is highly repressed in cells growing rapidly on glucose, which is in accord with prior induction-repression studies. Moreover, the lack of a change in uptake flux during the bulk of batch growth is consistent with prior induction-repression studies. (3) The mutant exhibits a heightened sensitivity to CO2 as compared to wild-type counterparts. Growth rate is increased, and the production of formate, malate, glycerate, and pyruvate is reduced. This sensitivity illustrates that citrate synthase is more than an expendable component in an amphibolic pathway. Its presence in wild-type cells "immunizes" against the effect of CO2 fluctuations. (4) The effects of CO2 can be tentatively explained by assuming that the PEP carboxylase-catalyzed reaction is stimulated.
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PMID:Flux adaptations of citrate synthase-deficient Escherichia coli. 783 22

We hypothesized that augmented responses of glucoregulatory hormones in iron deficiency would enhance liver and muscle glycogenolysis, leading to increased gluconeogenic precursor (lactate) supply and upregulation of hepatic gluconeogenesis. Female weanling rats were randomly placed on either a mildly iron-deficient (-Fe; 15 mg Fe/kg diet) or an iron-sufficient (+Fe; 50 mg Fe/kg diet) diet for 4 wk and studied at rest and during exhaustive treadmill running. Hemoglobin was 9.0 +/- 0.2 and 13.1 +/- 0.3 g/dl in -Fe and +Fe, respectively, after 3.5 wk of dietary iron deficiency. Arterial plasma epinephrine (Epi), norepinephrine (NE), adrenocorticotropic hormone (ACTH), corticosterone, insulin, and glucagon levels were similar at rest in both groups, as were liver, gastrocnemius, and superficial and deep vastus medialis glycogen levels. Liver and kidney phosphoenolpyruvate carboxykinase (PEPCK) activities were similar in both groups. Maximum O2 consumption was decreased (22%) in -Fe. Respiratory exchange ratio (CO2 production/O2 consumption) was unaffected at rest but increased at maximum O2 consumption in -Fe. Time to exhaustion during a standardized running test (13.4 m/min, 0% grade) was decreased 45% in -Fe (63 +/- 5 vs. 116 +/- 10 min). During exercise, euglycemia was maintained in both groups, but blood lactate was elevated in -Fe. The mean net glycogen utilization during exercise was increased in liver (43%), soleus (33%), and superficial vastus medialis (106%) and decreased in the gastrocnemius (36%) in -Fe. Liver and kidney PEPCK activities were increased similarly at exhaustion in both groups.(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:Augmented glucoregulatory hormone concentrations during exhausting exercise in mildly iron-deficient rats. 823 58

Incubation of Saccharomyces cerevisiae phosphoenolpyruvate carboxykinase with trypsin under native conditions cases a time-dependent loss of activity and the production of protein fragments. Cleavage sites determined by sodium dodecyl sulfate polyacrylamide gel electrophoresis and sequence analyses identified protease-sensitive peptide bonds between amino acid residues at positions 9-10 and 76-77. Additional fragmentation sites were also detected in a region approximately 70-80 amino acids before the carboxyl end of the protein. These results suggest that the enzyme is formed by a central compact domain comprising more than two thirds of the whole protein structure. From proteolysis experiments carried out in the presence of substrates, it could be inferred that CO2 binding specifically protects position 76-77 from trypsin action. Intrinsic fluorescence measurements demonstrated that CO2 binding induces a protein conformational change, and a dissociation constant for the enzyme CO2 complex of 8.2 +/- 0.6 mM was determined.
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PMID:Limited proteolysis of Saccharomyces cerevisiae phosphoenolpyruvate carboxykinase. 825 Oct 61

Although housekeeping functions have been shown for the phosphoenolpyruvate carboxylase (EC 4.1.1.31, PEPC) in plants and in prokaryotes, PEPC is mainly known for its specific role in the primary photosynthetic CO2 fixation in C4 and CAM plants. We have shown that in Sorghum, a monocotyledonous C4 plant, the enzyme is encoded in the nucleus by a small multigene family. Here we report the entire nucleotide sequence (7.5 kb) of the third member (CP21) that completes the structure of the Sorghum PEPC gene family. Nucleotide composition, CpG islands and GC content of the three Sorghum PEPC genes are analysed with respect to their possible implications in the regulation of expression. A study of structure/function and phylogenetic relationships based on the compilation of all PEPC sequences known so far is presented. Data demonstrated that: (1) the different forms of plant PEPC have very similar primary structures, functional and regulatory properties, (2) neither apparent amino acid sequences nor phylogenetic relationships are specific for the C4 and CAM PEPCs and (3) expression of the different genes coding for the Sorghum PEPC isoenzymes is differently regulated (i.e. by light, nitrogen source) in a spatial and temporal manner. These results suggest that the main distinguishing feature between plant PEPCs is to be found at the level of genes expression rather than in their primary structure.
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PMID:Sorghum phosphoenolpyruvate carboxylase gene family: structure, function and molecular evolution. 844 42

We studied the transition metal ion requirements for activity and sulfhydryl group reactivity in phospho enol pyruvate carboxykinase (PEP-carboxykinase; ATP:oxaloacetate carboxylase (transphosphorylating), EC 4.1.1.49), a key enzyme in the energy metabolism of the protozan parasite Trypanosoma (Schizotrypanum) cruzi. As for other PEP-carboxykinases this enzyme has a strict requirement of transition metal ions for activity, even in the presence of excess Mg2+ ions for the carboxylation reaction; the order of effectiveness of these ions as enzyme activators was: Co2+ > Mn2+ > Cd2+ > Ni2+ >> Fe2+ > VO2+, while Zn2+ and Ca2+ had no activating effects. When we investigated the effect of the varying type or concentration of the transition metal ions on the kinetic parameters of the enzyme the results suggested that the stimulatory effects of the transition metal center were mostly associated with the activation of the relatively inert CO2 substrate. The inhibitory effects of 3-mercaptopicolinic acid (3MP) on the enzyme were found to depend on the transition metal ion activator: for the Mn(2+)-activated enzyme the inhibition was purely non-competitive (Kii = Kis) towards all substrates, while for the Co(2+)-activated enzyme the inhibitor was much less effective, produced a mixed-type inhibition and affected differentially the interaction of the enzyme with its substrates. The modification of a single, highly reactive, cysteine per enzyme molecule by 5,5'-dithiobis (2-nitro-benzoate) (DTNB) lead ton an almost complete inhibition of Mn(2+)-activated T. cruzi PEP-carboxykinase; however, in contrast with the results of previous studies in vertebrate and yeast enzymes, the substrate ADP slowed the chemical modification and enzyme inactivation but did not prevent it. PEP and HCO3- had no significant effect on the rate or extent of the enzyme inactivation. The kinetics of the enzyme inactivation by DTNB was also dependent on the transition metal activator, being much slower for the Co(2+)-activated enzyme than for its Mn(2+)-activated counterpart. When the bulkier but more hydrophobic reagent N-(7-dimethylamino-4-methylcoumarinyl)maleimide (DACM) was used the enzyme was slowly and incompletely inactivated in the presence of Mn2+ and ADP afforded almost complete protection from inactivation; in the presence of Co2+ the enzyme was completely resistant to inactivation. Taken together, our results indicate that the parasite enzyme has a specific requirement of transition metal ions for activity and that they modulate the reactivity of a single, essential thiol group, different from the hyperreactive cysteines present in vertebrate or yeast enzymes.
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PMID:Trypanosoma cruzi phospho enol pyruvate carboxykinase (ATP-dependent): transition metal ion requirement for activity and sulfhydryl group reactivity. 854 43

In vivo, bicarbonate can affect proximal tubule intermediary metabolism, including gluconeogenesis, ammoniagenesis and maintenance of the mitochondrial substrate supply. In vitro, rabbit proximal tubule cells (RPTC) in primary culture revert from gluconeogenesis to glycolysis and their mitochondrial metabolism remains lower than in vivo. To determine whether the bicarbonate buffer system could have an effect on these deregulations, RPTC in primary culture grown in the absence of insulin and glucose in the culture medium were developed either with the standard sodium bicarbonate buffer with 5% CO2 or with a Hepes hydrogen ion buffer in the presence of 0.5% CO2. Duration of the bicarbonate-free cultures was increased until at least day 17 after seeding, compared with day 11 in bicarbonate-buffered cultures. As could be expected, succinate dehydrogenase activity remained stable as a function of time in bicarbonate-free cultures while an early marked decrease of this activity occurred from seeding in cultures developed in the presence of bicarbonate buffer. Compared to bicarbonate-buffered cells, higher phosphoenolpyruvate carboxykinase activity concomitant with lower intracellular lactate dehydrogenase activity was observed in cultures developed in the absence of bicarbonate, which is indicative of closer carbohydrate metabolism orientation to the in vivo situation for RPTC. Immunofluorescence staining of RPTC with monoclonal antibodies directed to neutral endopeptidase (NEP), and dipeptidyl-peptidase IV (DPP II) showed similar extensive labelling with DPP and NEP in both culture conditions. Confocal microscopy analysis of NEP subcellular distribution, showed exclusive targetting of NEP to the apical plasma membranes. In both models, cAMP production was stimulated by parathyroid hormone and unaffected by arginine vasopressin. In conclusion, bicarbonate withdrawal from the culture medium (without changing the pH of the medium) allows a marked improvement of mitochondrial capacity and carbohydrate metabolism pattern without any loss of differentiated properties.
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PMID:Effects of the medium HCO3-/CO2 buffer system on differentiation and intermediary metabolism properties of rabbit proximal tubule cells in primary culture. 897 88

Plants regulate water loss and CO2 gain by modulating the aperture sizes of stomata that penetrate the epidermis. Aperture size itself is increased by osmolyte accumulation and consequent turgor increase in the pair of guard cells that flank each stoma. Guard cell phosphoenolpyruvate carboxylase (PEPC, EC 4.1.1.31), which catalyzes the regulated step leading to malate synthesis, is crucial for charge and pH maintenance during osmolyte accumulation. Regulation of this cytosolic enzyme by effectors is well documented, but additional regulation by posttranslational modification is predicted by the alteration of PEPC kinetics during stomatal opening (FEBS Lett. 352, 45-48). In this study, we have investigated whether this alteration is associated with the phosphorylation status of this enzyme. Using sonicated epidermal peels ("isolated" guard cells) preloaded with 32PO4, we induced stomatal opening and guard cell malate accumulation by incubation with 5 microM fusicoccin (FC). In corroboratory experiments, guard cells were incubated with the FC antagonist, 10 microM abscisic acid (ABA). The phosphorylation status of PEPC was assessed by immunoprecipitation, electrophoresis, immunoblotting, and autoradiography. PEPC was phosphorylated when stomata were stimulated to open, and phosphorylation was lessened by incubation with ABA. Thus, we conclude that regulation of guard cell PEPC in vivo is multifaceted; the effects of regulatory metabolites and the activation status of the enzyme are integrated to control malate synthesis. These results, together with the coincident alteration in the kinetics of the enzyme (FEBS Lett. 352, 45-48), constitute the first unequivocal demonstration of regulatory posttranslational modification of a guard cell protein that is specifically implicated in stomatal movements.
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PMID:In vivo phosphorylation of phosphoenolpyruvate carboxylase in guard cells of Vicia faba L. is enhanced by fusicoccin and suppressed by abscisic acid. 901 32

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


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