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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. Tryptophan was administered to rats under various nutritional conditions: fasted for 24 hr, fasted and refed with glucose or corn-oil, fasted and administered glycerol intramuscularly, and nonfasted. 2. The changes in the contents of glycolytic intermediates in the livers indicated that the phosphoenolpyruvate carboxykinase [EC 4.1.1.32] reaction is inhibited by tryptophan administration in all groups of rats. The inversely related changes in the contents of malate and phosphoenolpyruvate were associated with the accumulation of quinolinate in the livers. The content of quinolinate which exhibited the half-maximal effect on the contents of both metabolites was 0.1-0.2 mumole per g liver. 3. The rate of incorporation of 3H from 3H2O into the total hepatic fatty acids was increased about 2-fold by the administration of this amino acid to the fasted rats. The enhancement of the rate was closely related to the increase in the citrate content. The hyperlipogenesis was also related to the decrease of acetyl-CoA and the increase of malonyl-CoA. The content of long-chain acyl-CoA was not affected. These effects of tryptophan administration on the hepatic fatty acid metabolism were found in all groups of rats. The liver content of glycerol 3-phosphate was decreased by tryptophan administration was markedly increased by glycerol injection. The injection of glycerol into the control and the tryptophan-treated rats produced a marked increase of glycerol 3-phosphate but did not affect the rate of fatty acid synthesis in the livers of either group. 4. It may be concluded that, in the livers of rats under various nutritional conditions, the short-term control of fatty acid synthesis by tryptophan administration is most likely due to the activation of acetyl-coenzyme A carboxylase [EC 6.4.1.2] by citrate.
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PMID:The effect of tryptophan administration on fatty acid synthesis in the livers of rats under various nutritional conditions. 0 Mar 75

Lipid synthesis as measured by the incorporation of acetate or 3H2O into slices of foetal liver, is much higher than in slices of adult liver and shows a peak at about two-thirds of gestation. At this time the synthesis from glucose was low and reached a peak 10 days later. The changes in the activity of ATP citrate lyase, which mirrored acetate incorporation, and the effect of glucose and pyruvate on acetate corporation into lipid suggests that some of the lipid synthesis occurs via intramitochondrial acetyl-CoA production from acetate. Despite this, lipid synthesis was not inhibited by (-)-hydroxycitrate. The low rate of synthesis from glucose at two-thirds of gestation is ascribed to the low activity of pyruvate carboxylase at this time and a role for a phosphoenolpyruvate carboxykinase in providing oxaloacetate for lipogenesis is proposed. The activity of fatty acid synthetase broadly agreed with the changes in lipid synthesis, whereas the activity of acetyl-CoA carboxylase was barely sufficient to account for the rates of lipid synthesis in vivo. Acetate and short-chain fatty acids are likely to be the major precursors for lipid synthesis in vivo.
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PMID:Lipid biosynthesis in liver slices of the foetal guinea pig. 0 15

Comparison of the activities of hexokinase, phosphorylase and phosphofructokinase in muscles from marine invertebrates indicates that they can be divided into three groups. First, the activities of the three enzymes are low in coelenterate muscles, catch muscles of molluscs and muscles of echinoderms; this indicates a low rate of carbohydrate (and energy) utilization by these muscles. Secondly, high activities of phosphorylase and phosphofructokinase relative to those of hexokinase are found in, for example, lobster abdominal and scallop snap muscles; this indicates that these muscles depend largely on anaerobic degradation of glycogen for energy production. Thirdly, high activities of hexokinase are found in the radular muscles of prosobranch molluscs and the fin muscles of squids; this indicates a high capacity for glucose utilization, which is consistent with the high activities of enzymes of the tricarboxylic acid cycle in these muscles [Alp, Newsholme & Zammit (1976) Biochem. J. 154, 689-700]. 2. The activities of lactate dehydrogenase, octopine dehydrogenase, phosphoenolpyruvate carboxykinase, cytosolic and mitochondrial glycerol 3-phosphate dehydrogenase and glutamate-oxaloacetate transaminase were measured in order to provide a qualitative indication of the importance of different processes for oxidation of glycolytically formed NADH. The muscles are divided into four groups: those that have a high activity of lactate dehydrogenase relative to the activities of phosphofructokinase (e.g. crustacean muscles); those that have high activities of octopine dehydrogenase but low activities of lactate dehydrogenase (e.g. scallop snap muscle); those that have moderate activities of both lactate dehydrogenase and octopine dehydrogenase (radular muscles of prosobranchs), and those that have low activities of both lactate dehydrogenase and octopine dehydrogenase, but which possess activities of phosphoenolpyruvate carboxykinase (oyster adductor muscles). It is suggested that, under anaerobic conditions, muscles of marine invertebrates form lactate and/or octopine or succinate (or similar end product) according to the activities of the enzymes present in the muscles (see above). The muscles investigated possess low activities of cytosolic glycerol 3-phosphate dehydrogenase, which indicates that glycerol phosphate formation is quantitatively unimportant under anaerobic conditions, and low activities of mitochondrial glycerol phosphate dehydrogenase, which indicates that the glycerol phosphate cycle is unimportant in the re-oxidation of glycolytically produced NADH in these muscles under aerobic conditions. Conversely, high activities of glutamate-oxaloacetate transaminase are present in some muscles, which indicates that the malate-aspartate cycle may be important in oxidation of glycolytically produced NADH under aerobic conditions. 3. High activities of nucleoside diphosphate kinase were found in muscles that function for prolonged periods under anaerobic conditions (e.g...
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PMID:The maximum activities of hexokinase, phosphorylase, phosphofructokinase, glycerol phosphate dehydrogenases, lactate dehydrogenase, octopine dehydrogenase, phosphoenolpyruvate carboxykinase, nucleoside diphosphatekinase, glutamate-oxaloacetate transaminase and arginine kinase in relation to carbohydrate utilization in muscles from marine invertebrates. 1 83

In alloxan diabetic rats a stimulatory effect of stress on the activity of liver phosphoenolpyruvate carboxykinase seems to be very likely. In intact animals the inhibitory effect of glucose feeding (15% glucose instead of laboratory diet and water) on the activity of liver tyrosine aminotransferase (TAT) and tryptophan pyrrolase was reconfirmed. Moreover, a reversal of this effect by immobilization for 2.5 h was observed. After a mean intake of 5.3 g glucose/100 g body weight during 16 h this reversal was only partial and after 3.4 glucose/100 g during the same time the glucose effect was abolished. Stimulation of both enzymes by corticosterone and of TAT by stress-induced release of glucagon may play a role in this reversal.
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PMID:Inhibitory effect of immobilization stress on depression of liver tyrosine aminotransferase and tryptophan pyrrolase by glucose feeding in rats. 1 21

Experimentally-induced alloxan diabetes was characterized in rats by a marked increase in the blood glucose level and by a number of disturbances in the concentration of metabolites and the activity of the enzymes of carbohydrate metabolism in the liver. Stimulation of gluconeogenesis in diabetes was judged by reduction of the redox condition of free NAD- and NADP-couples, by the increase in the concentration of phosphoenolpyruvate, malic oxaloacetate and phosphoenolpyruvate carboxykinase activity of the liver. Nicotinamide in a dose of 50 mg per 100 g of body weight caused a marked reduction in the blood glucose level of diabetic rats. An increase of the [NAD+]/[NADN], [NADP+]/[NADPN] ratio, a reduction of the concentration of phosphoenolpyruvate, malate and phosphoenolpyruvate carboxylase activity pointed to the inhibition of gluconeogenesis and stimulation of glycolysis in the liver of diabetic rats given nicotinamide.
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PMID:[Hypoglycemic effect of nicotinamide in rats with alloxan diabetes]. 2 43

Carbohydrate metabolism and vitamin-B6 status were assessed before and after pyridoxine administration in 46 women taking combined oestrogen-progestagen oral contraceptives (O.C.). 18 women had evidence of tissue depletion of vitamin B6, although all the women had abnormal tryptophan metabolism, including increased urinary xanthurenic acid (X.A.) excretion. In the women with vitamin B6 deficiency, administration of this vitamin caused elevation of fasting blood-pyruvate levels, and reduction in plasma glucose, insulin, and blood-pyruvate responses after an oral glucose load. These changes in carbohydrate metabolism were not found in the 28 non-vitamin-B6-deficient women. These results indicate that carbohydrate intolerance in women on O.C. is unlikely to be mediated by the formation of a complex of X.A. with insulin, as has formerly been proposed. Since the synthesis of the tryptophan metabolite quinolinic acid, an inhibitor of the heptaic enzyme phosphoenolpyruvate carboxykinase, may be enhanced by the administration of pyridoxine, it is suggested that this metabolite might be the important factor in the improvement of glucose tolerance in the vitamin-B6-deficient women. This conclusion is supported by the improvement in glucose tolerance observed in 6 women on O.C. and in 4 patients with glucocorticoid excess who were not vitamin-B6 deficient, when they were given tryptophan to augment the synthesis of quinolinic acid.
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PMID:Influence of oral contraceptives, pyridoxine (vitamin B6), and tryptophan on carbohydrate metabolism. 5 85

Experiments were performed in which the effects of inhibiting gluconeogenesis on ketone-body formation were examined in vivo in starved and severely streptozotocin-diabetic rats. The infusion of 3-mercaptopicolinate, an inhibitor of gluconeogenesis (DiTullio et al., 1974), caused decreases in blood [glucose] and increases in blood [lactate] and [pyruvate] in both normal and ketoacidotic rats. Patterns of liver gluconeogenic intermediates after 3-mercaptopicolinate infusion suggested inhibition at the level of phosphoenolpyruvate carboxykinase. This was confirmed by measurement of hepatic oxaloacetate concentrations which were increased 5-fold after 3-mercaptopicolinate administration. The infusion of 3-mercaptopicolinate caused a decrease in total ketone-body concentrations of 30% in starved rats and 73% in the diabetic animals. Blood glycerol and hepatic triglyceride concentrations remained unchanged. The decreases in ketone-body concentrations were associated with increases in the calculated hepatic cytosolic and mitochondrial [NADH]/[NAD+] ratios. The decrease in ketogenesis seen after inhibition of gluconeogenesis may have resulted from an inhibition of hepatic fatty acid oxidation by the more reduced mitochondrial redox state. It was concluded that gluconeogenesis may stimulate ketogenesis by as much as 30% in severe diabetic ketoacidosis.
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PMID:The effects of inhibition of gluconeogenesis on ketogenesis in starved and diabetic rats. 12 51

1. Approx. 85% of liver phosphoenolpyruvate carboxykinase is associated with the mitochondrial fraction in the fed guinea pig. Enzyme activity is unchanged in diabetes, but doubles during starvation. In contrast with earlier reports, both cytoplasmic and mitochondrial activities were found to be increased. 2. In kidney cortex, total enzyme activity is increased in both starved and diabetic animals. These changes are associated with increases in the cytoplasmic activity alone. 3. In diabetic animals the mean blood-glucose concentration was 23.1 mM. Other blood metabolites were lower than those in the rat, and the animals did not show significant ketosis. 4. Changes in the rates of gluconeogenesis from lactate and propionate paralleled those in phosphoenolpyruvate carboxykinase activity.
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PMID:The effects of starvation and experimental diabetes on phosphoenol-pyruvate carboxykinase in the guinea pig. 14 29

Cell suspensions of Bacteroides fragilis were allowed to ferment glucose and lactate labeled with (14)C in different positions. The fermentation products, propionate and acetate, were isolated, and the distribution of radioactivity was determined. An analysis of key enzymes of possible pathways was also made. The results of the labeling experiments showed that: (i) B. fragilis ferments glucose via the Embden-Meyerhof pathway; and (ii) there was a randomization of carbons 1, 2, and 6 of glucose during conversion to propionate, which is in accordance with propionate formation via fumarate and succinate. The enzymes 6-phosphofrucktokinase (pyrophosphate-dependent), fructose-1,6-diphosphate aldolase, phosphoenolpyruvate carboxykinase, malate dehydrogenase, fumarate reductase, and methylmalonyl-coenzyme A mutase could be demonstrated in cell extracts. Their presence supported the labeling results and suggested that propionate is formed from succinate via succinyl-, methylmalonyl-, and propionyl-coenzyme A. From the results it also is clear that CO(2) is necessary for growth because it is needed for the formation of C4 acids. There was also a randomization of carbons 1, 2, and 6 of glucose during conversion to acetate, which indicated that pyruvate kinase played a minor role in pyruvate formation from phosphoenolpyruvate. Phosphoenolpyruvate carboxykinase, oxaloacetate decarboxylase, and malic enzyme (nicotinamide adenine dinucleotide phosphate-dependent) were present in cell extracts of B. fragilis, and the results of the labeling experiments agreed with pyruvate synthesis via oxaloacetate and malate if these acids are in equilibrium with fumarate. The conversion of [2-(14)C]- and [3-(14)C]lactate to acetate was not associated with a randomization of radioactivity.
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PMID:Pathway of succinate and propionate formation in Bacteroides fragilis. 14 60

The activity of phosphoenolpyruvate carboxykinase (GTP) in Reuber H-35 cells was decreased after the removal of 6-N,2-O-dibutyryl adenosine 3':5'-monophosphate (dibutyryl cyclic AMP) from the medium. The decrease in activity was shown immunochemically to be the result of a rapid cessation in specific enzyme synthesis, occurring with a half-time of 40 min. The removal of dexamethasone, a less potent inducer of the enzyme in these cells, did not effect the activity of P-enolpyruvate carboxykinase or its rate of synthesis. Insulin added to either dibutyryl cyclic AMP or dexamethasone-treated cells produced a decline in specific enzyme synthesis which was not as rapid as that observed upon removal of dibutyryl cyclic AMP. This effect of insulin did not require the presence of glucose in the culture medium. Estimates of the half-life of the mRNA for P-enolpyruvate carboxykinase using actinomycin D and cordycepin suggested that after the inhibition of transcription of mRNA, enzyme synthesis continued for periods considerably longer than that observed after deinduction caused by removal of dibutyryl cyclic AMP. In addition, the synthesis of the enzyme could be restimulated by dibutyryl cyclic AMP in the absence of RNA synthesis. It was proposed that the deinduction of phosphoenolpyruvate carboxykinase in these cells is being regulated at the post-transcriptional or translational level.
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PMID:Deinduction of phosphoenolpyruvate carboxykinase (guanosine triphosphate) synthesis in Reuber H-35 cells. 16 66


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