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:4.1.1.32 (phosphoenolpyruvate carboxykinase)
4,204 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

A hybridocytochemical approach has been applied to establish whether the gene for the C/EBP mRNA might be involved in the topographical regulation of gene expression in adult rat liver. To that end the spatial distribution of the mRNA of C/EBP has been compared to that of the mRNAs of glutamine synthetase (GS), phosphoenolpyruvate carboxykinase (PEPCK) and glucokinase (GK) in normal adult livers, in livers from dexamethasone-treated animals and in livers from starved animals refed with glucose for 4 h. In normal rat liver, in situ hybridization with a probe for C/EBP mRNA revealed a low density of apparently homogeneously distributed grains, indicating low levels of C/EBP mRNA. In contrast, the livers of the experimentally-treated animals revealed a zonal distribution of the mRNA of C/EBP with the highest density of grains around the central venules. The dynamics of the pattern of expression of C/EBP mRNA are virtually identical to that of the GK mRNA. These data qualify C/EBP mRNA as a pericentral mRNA and suggest a role for the C/EBP protein in the topographical regulation of the expression of the GK mRNA.
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PMID:The dynamics of the expression of C/EBP mRNA in the adult rat liver lobulus qualifies it as a pericentral mRNA. 187 46

Perivenous and periportal hepatocytes were isolated by the digitonin/collagenase perfusion technique. The specific activity of phosphate-activated glutaminase was 2.33-fold higher in periportal cells than in perivenous cells. Similarly, the relative abundance of glutaminase mRNA was 2.6-fold higher in samples from periportal cells. The distribution of glutaminase activity and mRNA was compared with those for glutamine synthetase (predominantly perivenous) and phosphoenolpyruvate carboxykinase (predominantly periportal). The results suggest that phosphate-activated glutaminase is predominantly expressed in the periportal zone of the liver acinus.
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PMID:Distribution of hepatic glutaminase activity and mRNA in perivenous and periportal rat hepatocytes. 197 Feb 42

The expression of glutamine synthetase (GS) in the rat liver is dependent on pituitary growth hormone (GH). RNA blot hybridizations revealed that in hypophysectomized rats the level of glutamine synthetase mRNA was dramatically reduced in liver but not brain. This drop of GS mRNA in the liver results in a reduction of GS enzyme activity as well. Two other messages, phosphoenolpyruvate carboxykinase and glycerol phosphate dehydrogenase were not diminished in the liver, indicating that the effects of hypophysectomy on hepatic GS expression are specific and not part of a general reduction in transcription due to lack of pituitary factors. Daily administration of rat pituitary growth hormone caused an increase in the levels of hepatic GS mRNA as well as enzyme activity. In situ hybridization of normal liver sections with the GS antisense message showed an abundant amount of message confined to the region around each central vein of the hepatic acini, while in the hypophysectomized animal the message for GS is greatly reduced but still only located in hepatocytes surrounding the central vein. Hypophysectomized animals given GH replacement showed a substantial increase in the amount of exposed silver grains only around the central veins. This indicates that GH does not influence the cellular position of GS expression nor the viability of those hepatocytes that express the enzyme, but it does regulate the quantity of GS in the liver through changes in the levels of GS mRNA.
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PMID:Growth hormone regulation of hepatic glutamine synthetase mRNA levels in rats. 197 Mar 14

A hybridocytochemical analysis of adult liver from normal control and from hormonally and dietary-treated rats was carried out, using radioactively-labelled probes for the mRNAs of glutamine synthetase (GS), carbamoylphosphate synthetase (CPS) and phosphoenolpyruvate carboxykinase (PEPCK). In line with previous findings, GS mRNA is exclusively expressed in a small pericentral compartment, CPS mRNA exclusively in a contiguous large periportal compartment and PEPCK mRNA across the entire porto-central distance. The density of labelling in CPS and PEPCK mRNA-positive hepatocytes decreases in a porto-central direction. Starvation resulted in a reversal of the gradient of CPS mRNA within its periportal compartment; glucose refeeding counteracted this effect. Livers of glucocorticosteroid-treated, starved or diabetic rats also revealed a reversal of the normal gradient of CPS mRNA, but now across the entire porto-central distance. The patterns of expression of GS and PEPCK mRNA remained essentially unchanged, notwithstanding substantial changes in the levels of expression. It is concluded that blood-borne factors constitute the major determinants for the expression patterns of CPS mRNA within the context of the architecture of the liver lobulus.
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PMID:Diet- and hormone-induced reversal of the carbamoylphosphate synthetase mRNA gradient in the rat liver lobulus. 197 48

1. Glutamine was found to be the main carbon and nitrogen product of the metabolism of aspartate in isolated guinea-pig kidney-cortex tubules. Glutamate, ammonia and alanine were only minor products. 2. Carbon-balance calculations and the release of 14CO2 from [U-14C]aspartate indicate that oxidation of the aspartate carbon skeleton occurred. 3. A pathway involving aspartate aminotransferase, glutamate dehydrogenase, glutamine synthetase, phosphoenolpyruvate carboxykinase, pyruvate kinase, pyruvate dehydrogenase and enzymes of the tricarboxylic acid cycle is proposed for the conversion of aspartate into glutamine. 4. Evidence for this pathway was obtained by: (i) inhibiting aspartate removal by amino-oxyacetate, an inhibitor of transaminases, (ii) the use of methionine sulphoximine, an inhibitor of glutamine synthetase, which induced a large increase in ammonia release from aspartate, (iii) the use of quinolinate, an inhibitor of phosphoenolpyruvate carboxykinase, which inhibited glutamine synthesis from aspartate, (iv) the use of alpha-cyano-4-hydroxycinnamate, an inhibitor of the mitochondrial transport of pyruvate, which caused an accumulation of pyruvate from aspartate, and (v) the use of fluoroacetate, an inhibitor of aconitase, which inhibited glutamine synthesis with concomitant accumulation of citrate from aspartate.
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PMID:Glutamine synthesis from aspartate in guinea-pig renal cortex. 236 82

Katz et al. [Katz, J., Golden, S. & Wals, P.A. (1976) Proc. Natl Acad. Sci. USA 73, 3433-3437] were the first to report that in hepatocytes isolated from fasted rats and incubated with either dihydroxyacetone, glucose or other sugars, glycogen synthesis was greatly accelerated by addition of amino acids. We have looked for possible mediators responsible for this effect and have tested the effect of alanine, proline, asparagine, glutamine or a combination of ammonia with either pyruvate or lactate in activating glycogen synthesis from dihydroxyacetone. The following observations were made. 1. Stimulation of glycogen synthesis by alanine, proline or asparagine does not require production of glutamine since the effect also occurs in periportal hepatocytes which lack glutamine synthetase. 2. Under various conditions, stimulation of glycogen synthesis by added amino acids directly correlated with increases in the intracellular content of amino acids, expressed in osmotic equivalents. 3. 3-Mercaptopicolinic acid, the inhibitor of phosphoenolpyruvate carboxykinase, further enhances stimulation of glycogen synthesis by amino acids because it increases the intracellular accumulation of aspartate and glutamate. 4. The previously reported enhancement by leucine of the stimulation of glycogen synthesis by glutamine [Chen. K. S. & Lardy, H. A. (1985) J. Biol. Chem. 260, 14683-14688] can be ascribed to inhibition of urea synthesis by leucine which results in accumulation of glutamate and of ammonia, the essential activator of glutaminase. It is concluded that activation of glycogen synthesis by added amino acids is due to an increase in intracellular osmolarity following their uptake and the accumulation of intracellular catabolites. This results in an increase in hepatic volume which stimulates glycogen synthesis [Baquet, A., Hue, L., Meijer, A. J., van Woerkom, G. M. & Plomp, P. J. A. M. (1990) J. Biol. Chem. 265, 955-959].
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PMID:Stimulation of glycogen synthesis in hepatocytes by added amino acids is related to the total intracellular content of amino acids. 237 2

The submitochondrial localization of the four mitochondrial enzymes associated with urea synthesis in liver of Squalus acanthias (spiny dogfish), a representative elasmobranch, was determined. Glutamine- and acetylglutamate-dependent carbamoyl-phosphate synthetase, ornithine carbamoyltransferase, glutamine synthetase, and arginase were all localized within the matrix of liver mitochondria. The subcellular and submitochondrial localization and activities of several related enzymes involved in nitrogen metabolism and gluconeogenesis in liver and dogfish are also reported. Pyruvate carboxylase and phosphoenolpyruvate carboxykinase were localized in the mitochondrial matrix. Synthesis of citrulline by isolated mitochondria from ornithine proceeds at a near optimal rate at ornithine concentrations as low as 0.08 mM. The same stoichiometry and rates of citrulline synthesis are observed when ornithine is replaced by arginine. The mitochondrial location of arginase does not appear to reflect a mechanism for regulating ornithine availability.
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PMID:Submitochondrial localization of arginase and other enzymes associated with urea synthesis and nitrogen metabolism, in liver of Squalus acanthias. 286 47

The hypothesis that amiodarone (AM) acts by inducing a local 'hypothyroid-like' state in thyroid hormone-responsive tissues was investigated in rat liver. Hypothyroid rats, pretreated orally for 8 consecutive days with AM (200 mg/kg) or water, were given a single i.p. injection of equimolar doses of T4, T3 or rT3 (1.00 to 1.20 mg/kg). Six hours later, the rats were killed and liver nuclear T3 receptor occupancy was determined. Simultaneously, the activity of two thyroid hormone-responsive enzymes was measured, together with the levels of their respective mRNAs by hybridization to specific cDNAs. The enzymes were phosphoenolpyruvate carboxykinase and glutamine synthetase. AM showed no effect on nuclear T3 receptor occupancy in rats injected with either vehicle, rT3, or T3, but it completely blocked the increase in receptor occupancy in rats injected with T4. With regard to postreceptor effects, T4 and T3 elicited an approximately two-fold increase in the levels of the mRNAs coding for the two enzymes, whereas rT3 had no effect. The increase of the two mRNAs was potentiated by AM, but this is probably secondary to an AM-induced state of anorexia. Remarkably, this potentiating effect of AM was not observed at the protein-level: enzyme activities were lower in rats pretreated with AM. AM-pretreatment thus results in lower enzyme activity to mRNA ratios for both enzymes, irrespective of hormonal treatment. Therefore, although no conclusions can be drawn about possible effects of AM at the transcriptional level, it is concluded that AM interferes with thyroid hormone responsive gene expression in rat liver at a post-transcriptional level. As a consequence, in the present experimental design the livers of AM-treated rats resemble the liver of hypothyroid rats with regard to specific enzyme activities, but not with regard to either nuclear T3 receptor occupancy or the levels of specific mRNAs.
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PMID:Effects of amiodarone on thyroid hormone-responsive gene expression in rat liver. 289 59

Livers of starved rats refed for 2 h were perfused in situ by a modification of the dual digitonin pulse technique of Quistorff and Grunnet (Quistorff, B., and Grunnet, N. (1987) Biochem. J. 243, 87-95). A pulse of digitonin (2 mg/ml) was infused first antegrade through the portal vein followed retrograde through the vena cava, or in reverse order, 13 mg of digitonin per zone. Microscopic examination showed that this procedure permeabilized the periportal and perivenous zones of the liver without overlap, with a narrow unaffected band of hepatocytes between the zones. The distribution pattern between periportal and perivenous zones ratio for alanine transaminase, lactate hydrogenase, fructose-1,6-bisphosphatase, and phosphoenolpyruvate carboxykinase ranged from 1.5 to 3. Glucokinase activity was higher in the perivenous zone (periportal/perivenous ratio of 0.7) and glutamine synthetase was exclusively present in that zone. Fructose 2,6-bisphosphate concentration was nearly equal in the two zones.
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PMID:The zonation of liver and the distribution of fructose 2,6-bisphosphate in rat liver. 289 7

The liver is the "glucostat" of the organism and serves at the same time as an "ammonia-sink and pH stat". The key enzymes involved in glucose uptake and release and in urea and glutamine formation are reciprocally distributed over the liver parenchyma: The glucogenic enzymes phosphoenolpyruvate carboxykinase (PEPCK), fructosebisphosphatase (FBPase) and glucose-6-phosphatase (G6Pase) as well as the ureagenic enzyme carbamoylphosphate synthetase (CAPS) are predominant in the periportal zone. The glycolytic enzymes glucokinase (GK) and pyruvate kinase type L (PKL) as well as the glutaminogenic enzyme glutamine synthetase (GluNS) are prevalent in the perivenous zone. This heterogeneity appears to be a prerequisite for the normal "glucostat, ammonia-sink and pH-stat" function of the liver. After birth the liver is a gluconeogenic organ, only with weaning it becomes a "glycolytic/gluconeogenic" glucostat. In the rat zonation of PEPCK, G6Pase and CAPS developed gradually after birth and was completed before weaning, i.e. before it would be functionally required. After 2/3 partial hepatectomy the liver looses its normal glucostat function and becomes a gluconeogenic organ. With this change the zonation of PEPCK and PKL were also lost; it was restored only during the second week after operation. During starvation the liver also looses its glucostat function to become the major glucose supplier of the organism. Zonation of PEPCK and PKL were diminished to such an extent that the major function of the perivenous zone was altered from glucose uptake to release. In diabetes the liver does not loose its glucostat function; however, the function is severely impaired. Zonation of PEPCK was increased and that of PKL decreased in such a manner that the major function of the perivenous zone, glucose uptake, was not entirely changed but only diminished. It can be concluded that in the various physiological states studied the zonation of enzymes correlated well with the glucostat function of the liver.
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PMID:Dynamics of zonal hepatocyte heterogeneity. Perinatal development and adaptive alterations during regeneration after partial hepatectomy, starvation and diabetes. 301 Mar 76


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