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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 effects of metabolic acidosis and of hormones on the activity, synthesis, and degradation of renal cytosolic P-enolpyruvate carboxykinase (GTP) (EC 4.1.1.32) were studied in the rat using isotopic -immunochemical procedures. At normal acid-base balance, the synthesis of the enzyme accounted for between 2 and 3.5% of the synthesis of all soluble protein in the kidney cortex. P-enolpyruvate carboxykinase synthesis was selectively stimulated in acute metabolic acidosis, so that the relative rate of synthesis of the enzyme was increased to 7% 13 hours after oral administration of ammonium chloride. The stimulation of P-enolpyruvate carboxykinase synthesis preceded any increase in the assayable activity of the enzyme. The administration of sodium bicarbonate to acutely acidotic rats returned the rate of enzyme synthesis to normal in 8 hours. The effect of acidosis on both the synthesis and the activity of P-enolpyruvate carboxykinase was prevented by actinomycin D, cordycepin, and cycloheximide. The degradation in vivo of pulse-labeled P-enolpyruvate carboxykinase was not affected by acidosis. Thus, the stimulation of P-enolpyruvate carboxykinase synthesis is the major mechanism for the increase in the level of the enzyme observed in metabolic acidosis. The administration of glucocorticoid triamcinolone resulted in an increase in the relative rate of P-enolpyruvate carboxykinase synthesis and a commensurate increase in the activity of the enzyme in the renal cortex. Both changes were abolished by actinomycin D. Fasting was characterized by a high enzyme activity and a rapid rate of enzyme synthesis in the kidney cortex. This high rate of synthesis was reduced after the administration of sodium bicarbonate, but not after glucose feeding. Moreover, the injection of insulin to diabetic rats did not repress P-enolpyruvate carboxykinase synthesis in the renal cortex. Theophylline plus N-6, 0-2'-dibutyryl adenosine 3':5'-monophosphate stimulated P-enolpyruvate carboxykinase synthesis in the kidney of intact rats. However, the latter effect was probably due to glucocorticoid secretion, since it did not occur in adrenalectomized animals. The administration of parathyroid extracts did not result in the induction of the enzyme. Thus, the hormonal regulation of cytosolic P-enolpyruvate carboxykinase synthesis in the kidney differs markedly from that in the liver.
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PMID:The regulation of phosphoenolpyruvate carboxykinase (GTP) synthesis in rat kidney cortex. The role of acid-base balance and glucocorticoids. 16 19

The effect of cold exposure (5 degrees C) on the concentration of cyclic AMP and on the activity of phosphoenolpyruvate carboxykinase (GTP: oxaloacetate carboxy-lyase (transphosphorylating), EC 4.1.1.32) was investigated in the liver of intact and adrenalectomized starved rats. Intact starved rats responded to cold exposure with a large increase in both the concentration of hepatic cyclic AMP and the activity of phosphoenolpyruvate carboxykinase above the starvation level. Adrenalectomy did not impair the cold-induced maximum elevation of cyclic AMP but totally prevented the response of the enzyme to cold. Yet, this response was completely restored by hydrocortisone treatment, while the steroid per se had no effect on enzyme activity. In isolated perfused livers of intact starved rats dibutyryl cyclic AMP provoked an immediate dramatic increase in phosphoenolpyruvate carboxykinase activity above the starvation level even if mRNA synthesis was inhibited by cordycepin. However, cyclic AMP was ineffective in increasing enzyme activity in livers of adrenalectomized rats. From these results it is suggested (i) that in starved rats the adaptation to the enhanced glucose demand provoked by cold exposure includes the induction of hepatic phosphoenolpyruvate carboxykinase above the starvation level, (ii) that this induction is due to the cold-induced increase in hepatic cyclic AMP levels, (iii) that cyclic AMP stimulates enzyme synthesis at a post-transcriptional step and (iv) that the cold-induced cyclic AMP-mediated induction of phosphoenolpyruvate carboxykinase above the starvation level requires the "permissive" effect of glucocorticoids.
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PMID:Effect of cold exposure on phosphoenolpyruvate carboxykinase (GTP) activity and cyclic amp concentration in livers of starved rats. Role of glucorticoids. 18 3

In different metabolic states renal phosphoenolpyruvate carboxykinase (PEP-CK) activities are closely correlated with in vitro glucogenic rates, suggesting a limitation of the glucogenic capacity of kidney by this enzyme. Stimulation of renal gluconeogenesis from pyruvate, lactate, and succinate by lysine and glutamine was therefore associated with a regulatory attack of these amino acids at the level of PEP-carboxykinase. This postulate was confirmed by the failure of lysine to stimulate glucose synthesis from fructose. Experimental support for an interference of glutamine and PEP-carboxykinase was obtained by a study on the inactivation of this enzyme in kidney cortex homogenates: A rapid inactivation of enzyme activity within 40-50 min could be slowed down by glutamine. In addition the inactivation was counteracted by ATP. At suboptimal concentrations of the trinucleotide its effect was potentiated by c-AMP and c-GMP. Studies on the effect of ATP on PEP-carboxykinase in kidney cortex homogenates from rats in different metabolic states revealed: In homogenates from carbohydrate fed animals extreme low activities of PEP-CK were not altered by ATP, whereas elevated enzyme activities after a protein rich diet could be further raised by a factor of 2 or 3 by ATP. GTP and ITP could substitute for ATP. An extension of these studies on hepatic enzymes showed a similar inactivation of tyrosine aminotransferase (TAT) and a protective effect of ATP. The data obtained from these experiments favour an interconversion of PEP-carboxykinase and tyrosine aminotransferase into different forms as possible mechanism for their regulation.
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PMID:Regulation of phosphoenolpyruvate carboxykinase by glutamine and ATP as possible control mechanisms of renal gluconeogenesis. 18 82

The mechanism of the interaction between glucocorticoids and cyclic AMP in the regulation of phosphoenolpyruvate carboxykinase (GTP: oxalocetate carboxylase, transphosphorylating, EC 4.1.1.32) was investigated in the isolated perfused rat liver using inhibitors of transcription or translation. Dibutyryl cyclic AMP produced a rapid increase in P-enolpyruvate carboxykinase activity. The response of the enzyme to the cyclic nucleotide ceased however, at 4 h, but was restored by dexamethasone. The dibutyryl cyclic AMP-induced increase in P-enolpyruvate carboxykinase activity was completely blocked by cycloheximide, but not not by cordycepin. However, cordycepin totalaly suppressed the "permissive" effect of dexamethasone on the response of the enzyme to dibutyryl cyclic AMP. Preperfusion of the livers with dexamethasone and cycloheximide, following by perfusion without the steroid hormone and the inhibitor, resulted in a rapid rise in P-enolpyruvate carbosykinase activity, which was not affect by cordycepin. If livers were preperfused with cordycepin for different time-periods, followed by dibutyryl cyclic AMP stimulation of P-enolpyruvate carboxykinase synthesis, the response of the enzyme to the cyclic nucleotide was progressively reduced, achieving 50% inhibition after 1.5 h of preperfusion. These results suggest that the induction of hepatic P-enolpyruvate carboxykinase to maximum values, brought about by cyclic AMP at the level of translation, depends on the supply of newly synthetized mRNA provided by the transcriptional action of glucocorticoids.
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PMID:Interaction between glucocorticoids and cyclic AMP in the regulation of phosphoenolpyruvate carboxykinase (GTP) in the isolated perfused rat liver. Effects of cordycepin and cycloheximide. 18 61

The effect of re-feeding glucose, protein or fat and the effect of insulin injection on the activity of hepatic phosphoenolpyruvate carboxykinase (GTP: oxaloacetate carboxy-lyase (transphosphorylating) EC 4.1.1.32), the concentration of hepatic cyclic AMP and the level of serum insulin was investigated in starved rats. Under all conditions examined the concentration of serum insulin was elevated to a high degree. However, only rats re-fed with glucose responded to the increase in serum insulin with a decrease in PEP carboxykinase activity, while the activity of the enzyme remained unchanged or was elevated after re-feeding protein or fat or after insulin injection, respectively. Since under all conditions there was a close correlation between cyclic AMP concentration and PEP carboxykinase activity, but not between the insulin level and enzyme activity, it is concluded that the hormone physiologically regulates PEP carboxykinase activity by decreasing the intrahepatic cyclic AMP concentration rather than by the postulated cyclic AMP-independent inhibition of specific mRNA translation.
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PMID:Physiological regulation of rat liver phosphoenolpyruvate carboxykinase (GTP) by insulin. Insignificance of a cyclic AMP-independent mechanism. 19 43

Phosphoenolpyruvate carboxykinase (GTP) [GTP;oxaloacetate carboxy-lyase(transphosphorylating); EC 4.1.1.32] is absent in rat liver cytosol during fetal life and is synthesized initially at birth. De novo synthesis of the enzyme can be induced prematurely by injection of dibutyryl cyclic AMP or glucagon into fetal animals in utero. In this study a wheat germ translation assay was used to quantitate the level of total functional mRNA for phosphoenolpyruvate carboxykinase in the liver of fetal rats at 21 days of pregnancy under different induction situations. The translatable mRNA for the enzyme was marginally detectable in fetal rat liver. Administration of either glucagon or dibutyryl cyclic AMP to fetal rats in utero caused a marked induction of functional mRNA for this enzyme. Three hours after administration of dibutyryl cyclic AMP, the level of translatable mRNA increased almost 23-fold, but by 6 hr the level dropped approximately 60%. Administration of actinomycin D prior to dibutyryl cyclic AMP in 21-day fetal rats prevented the appearance of newly synthesized poly(A)-containing RNA in the cytoplasm as well as the induction of translatable mRNA for phosphoenolpyruvate carboxykinase. In animals delivered prematurely and maintained for varying periods, the translatable mRNA for the enzyme accumulated in the liver at a rate comparable to that observed for enzyme synthesis.
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PMID:Changes in hepatic messenger RNA for phosphoenolpyruvate carboxykinase (GTP) during development. 21 40

The cytosolic form of phosphoenolpyruvate carboxykinase (GTP; EC 4.1.1.32) from rat liver was purified by a procedure involving affinity chromatography on agarose-hydrazide-GTP. Phosphoenolpyruvate carboxykinase is retained quantitatively by the affinity medium in the presence of manganese and can be specifically eluted by a pulse of GTP. On the contrary, no binding to agarose-hydrazide-GTP occurs in the absence of manganese. This suggests that the affinity of the enzyme for GTP is enhanced by prior interaction with manganese. A combination of several conventional purification steps followed by affinity chromatography provides pure phosphoenolpyruvate carboxykinase in good yields. The final specific activity is 19 U/mg protein. The enzyme migrates as a single polypeptide of molecular weight 70,600 during electrophoresis on sodium dodecyl sulfate polyacrylamide gels.
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PMID:Purification of phosphoenolpyruvate carboxykinase (GTP) by affinity chromatography on agarose-hydrazide-GTP. 52 Feb 80

The content of acid-soluble nucleotides was different in the cells of non-sulphur purple bacterium Rhodospirillum rubrum, growing phototrophically under anaerobic conditions and aerobically under conditions of heterotrophic nutrition. The cells of the culture growing in the darkness contained more adenylic and guanylic nucleotides, and the total of reduced and oxidized NADP. The cells of the culture growing in the light contained more FMN. The cells of the "light" and "dark" cultures contained GTP dependent phosphopyruvate carboxylase (E.C. 4.1.1.32). The cells of the "light" culture, contrary to the "dark" culture, contained also pyrophosphate dependent phosphopyruvate carboxylase (E.C. 4.1.1.38).
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PMID:[Acid-soluble nucleotides of the phototrophic bacterium Rhodospirillum rubrum during growth in light and in darkness]. 81 80

Timed assays in which GTP and GDP were separated and quantitated by HPLC were developed and used to study the metal activation of the mitochondrial and cytosolic isozymes of phosphoenolpyruvate carboxykinase purified from rabbit liver. These assays allowed both directions of catalysis to be studied under similar conditions and in the absence of coupling enzymes. The mitochondrial enzyme is rapidly inactivated by preincubation with Fe2+, as had been shown previously for the cytosolic isozyme. The greatest activation by Fe2+ was obtained by adding micromolar Fe2+ immediately after enzyme to form the complete assay mixture that also contained millimolar Mg2+. In the direction of synthesis of OAA from Pep, the K0.5 values for Mn2+ and Fe2+ were in the 3-7 microM range when a nonchelating buffer, Hepes, was used. The buffer used strongly affected activation by Fe2+ at pH 7.4; activation was eliminated in the case of phosphate and K0.5 increased several-fold over that obtained with Hepes when imidazole was used. In non-chelating buffer, the pH optimum was near 7.4 for both isozymes and for both directions of catalysis. However, the near optimal pH range extended below 7.4 for the direction of oxaloacetate synthesis while the range was above 7.4 for Pep synthesis. In the direction of oxaloacetate synthesis: (1) Both isozymes required the presence of micromolar Mn2+ or Fe2+ in addition to millimolar Mg2+ in order to shown significant activity. (2) Fe2+ was as effective an activator as Mn2+ at pH 7 and below. In the direction of Pep synthesis: (1) Micromolar Mn2+ was a much better activator than Fe2+ at the higher pH values needed for optimal activity in this direction. (2) With increasing pH, decreasing activation was obtained with Fe2+ while the activity supported by Mg2+ alone increased. The results demonstrate the potential for regulation of either isozyme of Pep carboxykinase by the availability of iron or manganese.
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PMID:Factors affecting the manganese and iron activation of the phosphoenolpyruvate carboxykinase isozymes from rabbit. 147 44

2-Oxoglutarate was found to inhibit purified rat liver phosphoenolpyruvate carboxykinase when the assay was performed in the direction of either phosphoenolpyruvate or oxaloacetate synthesis. The inhibition was competitive with respect to oxaloacetate or phosphoenolpyruvate, the Ki values being 0.32 +/- 0.04 mM 0.63 +/- 0.19 mM respectively. 2-Oxoglutarate inhibited non-competitively when tested against GTP or Mn2+. The reported cytosolic concentrations of 2-oxoglutarate in rat hepatocytes are such that the enzyme is likely to be significantly inhibited under basal conditions. The cytosolic concentration of 2-oxoglutarate is known to fall precipitously under the influence of glucagon and other hormones that stimulate gluconeogenesis, and it is suggested that the hormone-induced decrease in 2-oxoglutarate content would alleviate the inhibition of phosphoenolpyruvate carboxykinase and stimulate flux from oxaloacetate to phosphoenolpyruvate. The implications of this finding to the rationalization of the role of pyruvate kinase in the stimulation of gluconeogenesis in the fasted state are discussed.
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PMID:Physiological concentrations of 2-oxoglutarate regulate the activity of phosphoenolpyruvate carboxykinase in liver. 149 14


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