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:4.1.1.49 (phosphoenolpyruvate carboxykinase)
4,654 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

1. Naturally-occurring and synthetic analogues of phenylalanine, tyrosine, histidine, arginine, proline, tryptophan and the sulphur amino acids have beeen tested in rat reticulocytes and in the Reuber H35 hepatoma for effects on protein synthesis and protein degradation and on the heat lability of phosphoenolpyruvate carboxykinase (EC 4.1.1.32) in the hepatoma cells. The experiments were designed to test whether the analogues could be incorporated into mammalian proteins and whether the resultant proteins would be degraded at an accelerated rate. 2. Several analogues, including thiazolylanine, triazolalanine and selenocystine both stimulated protein synthesis and produced labile protein in reticulocytes. Other analogues, such as dihydroxyphenylalanine, thioproline and pipecolic acid accelerated protein breakdown but probably indirectly via an inhibition of protein synthesis. Azetidine-2-carboxylic acid had the largest effect on protein breakdown in reticulocytes. 3. Labile protein was produced in hepatoma cells incubated in the presence of azetidine-2-carboxylic acid, canavanine, indospicine, triazolalanine, 2-, 3- and 4-fluorophenylalanine. These same analogues, together with 3,4-dehydroproline, beta-2-thienylalanine, dihydroxyphenylalanine, histidinol, 5- and 6-fluorotryptophan, selenocystine and selenomethionine produced heat-labile phosphoenolpyruvate carboxykinase. Enzyme induced in the presence of selenomethionine or indospicine showed the largest increases in heat lability, and for these analogues equimolar concentrations of methionine and arginine respectively were needed to nullify the enzyme abnormality. 4. The toxicity of the same naturally-occurring analogues has been discussed in terms of their ability to be incorporated into cell proteins.
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PMID:Effects of amino acid analogues on protein synthesis and degradation in isolated cells. 21 95

Metabolic responses associated with prolonged fasting and subsequent refeeding of pigs were investigated. Fasting for 14 or 28 days produced significant increases in serum levels of alanine, aspartic and glutamic acid in the three branched-chain amino acids. Glycine, serine and lysine levels were elevated after 28 days of fasting while the levels of histidine, methionine, threonine and phenylalanine were reduced. Fasting markedly stimulated hepatic and renal gluconeogenesis and the activity of the urea cycle enzymes. Fatty acid synthesis and glucose oxidation were virtually abolished in hepatic and adipose tissue in pigs subjected to a 14- or 28-day fast. After the first day of refeeding, the levels of amino acids returned to the control values. The activity of the hepatic urea cycle enzymes, fructose-1,6-diphosphatase and phosphoenolpyruvate carboxykinase remained elevated after the first day of refeeding but returned to the control levels thereafter. The activity of hepatic glucose-6-phosphate dehydrogenase, malic dehydrogenase and acetyl CoA carboxylase were slightly enhanced in pigs refed for 4 and 8 days. The activity of these enzymes in adipose tissue was enhanced 8 days after refeeding. Hepatic synthesis of fatty acids from glucose was slightly stimulated in refed pigs on days 4 and 8 but returned to control values on day 16. Refeeding did not enhance glucose incorporation into fatty acids in adipose tissue above the values observed in fed controls.
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PMID:Metabolic responses to prolonged fasting and subsequent refeeding in the pig. 55 35

Ochratoxin A has a number of toxic effects in mammals, the most notable of which is nephrotoxicity. It is also immunosuppressive, teratogenic and carcinogenic. The biochemical and molecular aspects of its action were first studied in bacteria. The appearance of 'magic spots' (ppGpp and pppGpp) pointed to inhibition of the charging of transfer ribonucleic acids (tRNA) with amino acids. This suggestion was confirmed by the demonstration that ochratoxin A inhibits bacterial, yeast and liver phenylalanyl-tRNA synthetases. The inhibition is competitive to phenylalanine and is reversed by an excess of this amino acid. As a consequence, protein synthesis is inhibited, as shown with hepatoma cells in culture, with Madin Darby canine kidney cells (which are much more sensitive) and in vivo in mouse liver, kidney and spleen, the inhibition being more effective in the latter two organs. An excess of phenylalanine also prevents inhibition of protein synthesis in cell cultures and in vivo. Analogues of ochratoxin A in which phenylalanine has been replaced by other amino acids have similar inhibitory effects on the respective amino acid-specific aminoacyl tRNA synthetases. 4R-Hydroxyochratoxin A, a metabolite of ochratoxin A, has a similar action, whereas ochratoxin alpha (the dihydroisocoumarin moiety) and ochratoxin B (ochratoxin A without chlorine) have no effect. Ochratoxin A might act on other enzymes that use phenylalanine as a substrate. We showed recently that it inhibits phenylalanine hydroxylase. In addition, the phenylalanine moiety of ochratoxin A is partially hydroxylated to tyrosine by incubation with hepatocytes and in vivo. This competitive action with phenylalanine might explain why this amino acid prevents the immuno-suppressive effect of ochratoxin A and partially prevents its teratogenic and nephrotoxic actions. The effect of ochratoxin A on protein synthesis is followed by an inhibition of RNA synthesis, which might affect proteins with a high turnover. Ochratoxin A also lowers the level of phosphoenolpyruvate carboxykinase, a key enzyme in gluconeogenesis; this inhibition is reported to be due to a specific degradation of mRNA that codes for this enzyme. Recently, ochratoxin A was also found to enhance lipid peroxidation both in vitro and in vivo. This inhibition might have an important effect on cell or mitochondrial membranes and be responsible for the effects on mitochondria that have been shown by several authors. Finally, the recent results of Pfohl-Leszkowicz et al. (this volume), who showed the formation of DNA adducts mainly in kidney but also in liver and spleen, explain the DNA single-strand breaks observed previously in mice and rats after acute and chronic treatment.
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PMID:Mechanism of action of ochratoxin A. 182 Mar 32

Twenty obese and 20 lean LA/N-cp male rats and 20 male Sprague-Dawley rats were fed a diet containing either 54 percent sucrose or starch for six weeks. After a 14-16 hour fast, rats were killed. Liver and kidney enzyme activities were determined in the LA/N-cp rats while plasma urea and selected amino acids were determined in all rats. Liver glucose-6-phosphatase (G6PASE), fructose-1,6-bisphosphatase (FBPASE), phosphoenolpyruvate carboxykinase (PEPCK), glucose-6-phosphate dehydrogenase (G6PDH), 6-phosphogluconate dehydrogenase (6PGDH), malic enzyme (ME), glucokinase (GK), pyruvate kinase (PK), phosphofructokinase (PFK), glutamic-oxaloacetic-transaminase (GOT), glutamic-pyruvic transaminase (GPT), arginase (ARGASE), arginine-synthase (ARG-SYN) and ornithine transcarbamylase (OTC) levels were significantly affected by phenotype (obese greater than lean). All the above changes in enzyme levels were exaggerated by sucrose-feeding with the exception of PK, PFK, GOT, GPT, ARGASE and ARG-SYN. Kidney cortex G6PASE, PEPCK and ARGASE activities were higher in the obese rats as compared to the lean littermates. Sucrose feeding resulted in higher cortex G6PASE, FBPASE and PEPCK as compared to starch-fed rats. A phenotype effect was noted with plasma glutamate, urea, leucine, isoleucine and valine (obese greater than lean) and a diet effect was seen with aspartate, phenylalanine, leucine and valine (sucrose greater than starch) concentration. Sprague-Dawley rats had higher plasma urea and lower alanine than lean LA/N-cp males. Metabolic obesity in the LA/N-cp rat appears to involve an elevated capacity for pathways of glycolysis, gluconeogensis, lipogenesis and amino acid catabolism in the liver.
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PMID:Effect of dietary carbohydrate on liver and kidney enzyme activities and plasma amino acids in the LA/N-cp rat. 204 12

We have studied factors regulating the rate of protein degradation in cultured hepatocytes obtained from 17-day-old fetal, 7-day-old suckling, and 20-day-old weanling rats. At all three stages of development 60-70% of protein degradation was sensitive to inhibition by amino acids and 3-methyladenine, an inhibitor of macroautophagy, indicating a major role of the lysosomes in proteolysis under these conditions. A combination of dibutyryl cyclic AMP and dexamethasone strongly stimulated proteolysis in hepatocytes from weanling, but not from fetal and suckling rats. The stimulatory effect of these compounds was eliminated at high amino acid concentrations in the culture medium. Cultured perinatal hepatocytes responded to exposure to dibutyryl cyclic AMP and dexamethasone by de novo synthesis of mRNA for carbamoyl-phosphate synthase and for phosphoenolpyruvate carboxykinase, demonstrating that the developmental change in the effect of dibutyryl cyclic AMP and dexamethasone on proteolysis was due to a developmental change in the regulation of proteolysis. An analysis of the changes in intracellular amino acid concentrations in response to variations in the extracellular amino acid concentrations at all three stages of development showed that of all amino acids that could be identified, only Ile, Leu, Lys, Phe, and Tyr are implicated as possible regulators of hepatic proteolysis. Dibutyryl cyclic AMP and dexamethasone did not affect the intracellular concentrations of these amino acids, showing that hormonal regulation of proteolysis is not mediated by changes in intracellular concentrations of these amino acids. It is concluded that the lack of sensitivity of the proteolytic system to catabolic hormones in the period around birth, combined with higher circulating plasma amino acid concentrations, are mechanisms contributing to the low rate of intrahepatic proteolysis in vivo in the perinatal period and thus to the rapid growth of the liver in this period.
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PMID:Effects of intracellular amino acid concentrations, cyclic AMP, and dexamethasone on lysosomal proteolysis in primary cultures of perinatal rat hepatocytes. 838 May 74

Phenylalanine hydroxylase catalyzes the major regulatory step of the phenylalanine degradation pathway. In view of the glucogenic nature of phenylalanine breakdown, and hence its potential contribution to glucose homeostasis, we have investigated the impact of streptozotocin-induced diabetes upon the expression of rat phenylalanine hydroxylase. Northern blot analysis revealed that induction of diabetes was associated with an increase in the in vivo abundance of hepatic phenylalanine hydroxylase-specific mRNA. This increase in mRNA abundance was maintained for at least 8 hr in liver cells isolated from diabetic animals. In contrast, phenylalanine hydroxylase immunoreactivity and enzymic activity decreased, over the 8 hr incubation period, to levels similar to those observed in liver cells from normal animals. These changes were retarded, but not prevented, by the presence of dexamethasone in incubation media. In liver cells from normal animals the abundance of phenylalanine hydroxylase-specific mRNA, immunoreactivity and enzymic activity, were largely insensitive to treatment with dexamethasone and/or glucagon over an 8 hr incubation period. It is concluded that, whereas diabetes-related alterations in phenylalanine hydroxylase-specific mRNA abundance persist after isolation of liver cells, changes in phenylalanine hydroxylase protein abundance do not. Additionally, in contrast to certain other enzymes (e.g. phosphoenolpyruvate carboxykinase) it is not possible to mimic diabetes-related alterations in the expression of phenylalanine hydroxylase, in liver cells from normal animals, by simple hormonal manipulation of incubation media. This implies that other additional factors must also contribute to diabetes-related alterations in hepatic enzyme expression.
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PMID:Differential effects of streptozotocin-induced diabetes on phenylalanine hydroxylase protein and mRNA abundance in isolated rat liver cells. 892 6

The in vitro differentiation of Trypanosoma brucei from bloodstream to procyclic (insect) forms is accompanied by diminishing variant surface glycoprotein (VSG) and increasing levels of procyclin and phosphoenolpyruvate carboxykinase (PEPCK). In this study, we examined the fate of several glycolytic enzymes of T. brucei during differentiation. We observed a down-regulation of glycosomal phosphoglycerate kinase (gPGK) during differentiation. In contrast, intracellular levels of glycosomal glyceraldehyde-3-phosphate dehydrogenase (gGAPDH), aldolase (ALD), and phosphoglucoisomerase (PGI) remained unchanged during differentiation and apparently continued to be synthesized in the procyclic form. To determine the potential role of proteasomes and other proteases during the differentiation process, we tested the effect of lactacystin, a specific inhibitor of proteasome activity, and morpholinourea-Phe-homoPhe-benz-alpha-pyrone (P27), a selective inhibitor of cysteine proteases, on the in vitro differentiation of T. brucei. Cells differentiated normally in the presence of 1 microM lactacystin, which confirmed our previous observation that this differentiation does not require crossing any phase boundaries in the cell cycle (Mutomba and Wang, Mol Biochem Parasitol 1996;80:89-102). But the cells thus differentiated did not increase in number and retained gPGK. Cells differentiated under 2 microM P27 also proceeded at a normal rate but failed to multiply and retained gPGK. However, most of the differentiated cells under 2 microM P27 also retained VSG on the cell membrane surface and expressed higher levels of procyclin suggesting that a cysteine protease(s) may be involved in releasing VSG and partially reducing procyclin during differentiation. This cysteine protease(s) has been tentatively identified in the procyclic cells as a 48 kDa protein through labeling of cysteine protease(s) with a biotinylated P27 homolog K02 (morpholinourea-Phe-homoPhe-vinylsulfone).
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PMID:The role of proteolysis during differentiation of Trypanosoma brucei from the bloodstream to the procyclic form. 966 24

In Escherichia coli, aspartate aminotransferase (encoded by aspC) and aromatic amino acid aminotransferase (encoded by tyrB) share overlapping substrate specificity in the syntheses of aromatic amino acids. Through the transamination reactions catalyzed by AspC or TyrB, L-phenylalanine (L-Phe) can be produced from phenylpyruvate with aspartic acid as the amino donor. To modulate and enhance the production levels of proteins, both aspC and tyrB were subcloned into a runaway-replication vector. As a result, the specific activities of AspC and TyrB obtained showed 65-fold and 50-fold increases, respectively, compared with the wild-type level. Employing resting cells of AspC- and TyrB-overproducing E. coli K-12 strains for L-Phe productions resulted in molar conversion yields of 70% and 55%, respectively. With an additional introduction of phosphoenolpyruvate carboxykinase (encoded by pck) into the transamination reactions, the conversion yields were improved to 93% from 70% and to 75% from 55% in a relatively short time. These results account for more than an 8-fold increase in productivity, as compared to the previous report (Calton et al., 1985). In addition, a four-run reuse of the recombinant cells for L-Phe production gave a total yield of 91 g/L with a 93% conversion.
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PMID:Enhanced conversion rate of L-phenylalanine by coupling reactions of aminotransferases and phosphoenolpyruvate carboxykinase in Escherichia coli K-12. 1035 62

Experimental design of (13)C-tracer studies for metabolic flux analysis with mass spectrometric determination of labeling patterns was performed for the central metabolism of Corynebacterium glutamicum comprising various flux scenarios. Ratio measurement of mass isotopomer pools of Corynebacterium products lysine, alanine, and trehalose is sufficient to quantify the flux partitioning ratios (i) between glycolysis and pentose phosphate pathways (Phi(PPP)), (ii) between the split pathways in the lysine biosynthesis (Phi(DH)), (iii) at the pyruvate node (Phi(PC)), and reversibilities of (iv) glucose 6-phosphate isomerase (zeta(PGI)), (v) at the pyruvate node (zeta(PC/PEPCK)), and (vi) of transaldolase and transketolases in the PPP. Weighted sensitivities for flux parameters were derived from partial derivatives to quantitatively evaluate experimental approaches and predict precision for estimated flux parameters. Deviation of intensity ratios from ideal values of 1 was used as weighting function. Weighted flux sensitivities can be used to identify optimal type and degree of tracer labeling or potential intensity ratios to be measured. Experimental design for lysine-producing strain C. glutamicum MH 20-22B (Marx et al., Biotechnol. Bioeng. 49, 111-129, 1996) and various potential mutants with different alterations in the flux pattern showed that specific tracer labelings are optimal to quantify a certain flux parameter uninfluenced by the overall flux situation. Identified substrates of choice are [1-(13)C]glucose for the estimation of Phi(PPP) and zeta(PGI) and a 1 : 1 mixture of [U-(12)C/U-(13)C]glucose for the determination of zeta(PC/PEPCK). Phi(PC) can be quantified by feeding [4-(13)C]glucose or [U-(12)C/U-(13)C]glucose (1 : 1), whereas Phi(DH) is accessible via [4-(13)C]glucose. The sensitivity for the quantification of a certain flux parameter can be influenced by superposition through other flux parameters in the network, but substrate and measured mass isotopomers of choice remain the same. In special cases, reduced labeling degree of the tracer substrate can increase the precision of flux analysis. Enhanced precision and flux information can be achieved via multiply labeled substrates. The presented approach can be applied for effective experimental design of (13)C tracer studies for metabolic flux analysis. Intensity ratios of other products such as glutamate, valine, phenylalanine, and riboflavin also sensitively reflect flux parameters, which underlines the great potential of mass spectrometry for flux analysis.
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PMID:Modeling and experimental design for metabolic flux analysis of lysine-producing Corynebacteria by mass spectrometry. 1128 93

We report crystal structures of the human enzyme phosphoenolpyruvate carboxykinase (PEPCK) with and without bound substrates. These structures are the first to be determined for a GTP-dependent PEPCK, and provide the first view of a novel GTP-binding site unique to the GTP-dependent PEPCK family. Three phenylalanine residues form the walls of the guanine-binding pocket on the enzyme's surface and, most surprisingly, one of the phenylalanine side-chains contributes to the enzyme's specificity for GTP. PEPCK catalyzes the rate-limiting step in the metabolic pathway that produces glucose from lactate and other precursors derived from the citric acid cycle. Because the gluconeogenic pathway contributes to the fasting hyperglycemia of type II diabetes, inhibitors of PEPCK may be useful in the treatment of diabetes.
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PMID:Crystal structure of human cytosolic phosphoenolpyruvate carboxykinase reveals a new GTP-binding site. 1185 36


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