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)

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

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

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

The gluconeogenic capacity of mammary tissue of lactating cow was investigated by incubating mammary tissue slices with alanine, glutamate, lactate, pyruvate, or glycerol in conjunction with acetate and glucose (10mM or 1 mM). In no case was any substrate incorporated into glucose per se. In lactose synthesis, glucose was the major source of carbon although glycerol also was incorporated into lactose. Alanine, glutamate, lactate, or pyruvate were not incorporated into lactose at optimum (10 mM) or suboptimum (1 mM) concentrations of glucose. Activity of glucose-6-phosphatase was negligible in mammary tissue, less than 1% of the activity in liver or kidney tissue from the same cows. Pyruvate carboxylase, phosphoenolpyruvate carboxykinase, and fructose-1,6-diphosphatase were in cow mammary tissue, but the activities were lower than in liver. Gluconeogenic substrates were not converted to glucose regardless of whether the incubation contained an optimum (10 mM) or a suboptimum (1 mM) glucose concentration. Consistent with the inability of cow mammary tissue to convert gluconeogenic metabolites to glucose is the virtual absence of glucose-6-phosphatase and the lack of excess gluconeogenic substrates available to the intact mammary gland of lactating cow.
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PMID:Cellular gluconeogenesis by lactating bovine mammary tissue. 17 3

1. The development of glycerolkinase before and after birth was investigated in liver and kidney of rat and hamster. In rat liver, enzyme activity increased very slowly before birth and rapidly thereafter, reaching adult values at the 6th day of postnatal life. In hamster liver, glycerolkinase was considerably elevated already in utero, increased dramatically within the 1st day of postnatal life and reached adult values at the end of the 1st week. The development of hepatic glycerolkinase was compared with that of hepatic phosphoenolpyruvate carboxykinase of rat and hamster up to the 20th day of postnatal life. The different time-courses of the levels of these two enzymes before and after birth as well as the known kinetics of serum insulin, glucagon and corticosterone during that time suggested that none of these hormones is involved in the perinatal development of hepatic glycerolkinase activity. In contrast to liver, kidney glycerolkinase activity in both, rat and hamster, showed a delayed increase during the first week of postnatal life followed by a more pronounced elevation to adult values within the following 2 weeks. 2. When liver and kidney glycerolkinase activity was investigated during starvation (+/- refeeding), in alloxan diabetes(+/- insulin) and after adrenalectomy (+/- cortisol) no significant change in enzyme activity per g tissue could be detected either in liver or in kidney. However, total hepatic glycerolkinase activity was diminished during starvation as a consequence of decreasing liver weight. 3. Incorporation of U-[14C]-glycerol into CO2, lipids and glucose + glycogen by rat liver and kidney cortex slices was studied under the above gluconeogenetic conditions. Despite unchanged glycerolkinase activity in both organs, gluconeogenesis from glycerol was enhanced during starvation and in chronic alloxan diabetes, and could be reversed by refeeding and insulin replacement, respectively. 4. Feeding 20% of linolic acid to normal, alloxan-diabetic or adrenalectomized rats resulted in a significant increase in glycerolkinase activity in liver but not in kidney. 5. From the present findings it is suggested that the first step of gluconeogenesis from glycerol in liver and kidney is not influenced by glucagon, insulin and glucocorticoids, which are generally believed to regulate the rate of gluconeogenesis from non-glycerol precursors, but probably by the change in blood glycerol concentration.
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PMID:Glycerolkinase--a regulatory enzyme of gluconeogenesis? 18 91

1. Activities of 3-oxo acid CoA-transferase and carnitine palmitoyltransferase together with tri- and di-acylglycerol lipase were present in red and heart muscles of the teleost fish. However, d-3-hydroxybutyrate dehydrogenase activity was not detectable. These results suggest that the heart and red muscles of the teleosts should be able to utilize the fat fuels triacylglycerol, fatty acids or acetoacetate, but not hydroxybutyrate. The muscles from the elasmobranchs differed in that d-3-hydroxybutyrate dehydrogenase and 3-oxo acid CoA-transferase activities were present, but carnitine palmitoyltransferase activity was not detectable. This suggests that ketone bodies are the most important fat fuels in elasmobranchs. 2. The concentrations of acetoacetate, 3-hydroxybutyrate, glycerol, non-esterified fatty acids and triacylglycerols were measured in blood or plasma of several species of fish (teleosts and elasmobranchs) in the fed state. Teleosts have a 10-fold higher concentration of plasma non-esterified fatty acids, but a lower blood concentration of ketone bodies; both acetoacetate and 3-hydroxybutyrate are present in blood of elasmobranchs, whereas 3-hydroxybutyrate is absent from that of the teleosts. 3. The effects of starvation (up to 150 days) on the concentrations of blood metabolites were studied in a teleost (bass) and an elasmobranch (dogfish). In the bass there was a 60% decrease in blood glucose after 100 and 150 days starvation. In dogfish there was a large increase in the concentration of ketone bodies, whereas in bass the concentration of acetoacetate (the only ketone body present) remained low (<0.04mm) throughout the period of starvation. The concentration of plasma non-esterified fatty acids increased in bass, but decreased in dogfish. These changes are consistent with the predictions based on the enzyme-activity data. 4. Starvation did not change the activities of ketone-body-utilizing enzymes or that of phosphoenolpyruvate carboxykinase in heart and red skeletal muscles of both fish, but it decreased markedly the activity of phosphoenolpyruvate carboxykinase in white skeletal muscle of both fish. However, in the liver of the dogfish, starvation resulted in a twofold increase in the activities of 3-hydroxybutyrate dehydrogenase and acetoacetyl-CoA thiolase, whereas in bass liver it decreased the activity of acetoacetyl-CoA thiolase and increased that of 3-oxo acid CoA-transferase. The activity of phosphoenolpyruvate carboxykinase was increased twofold in the liver of bass, but was unchanged in that of the dogfish. 5. The difference in changes in concentrations of blood metabolites and enzyme activities in the two fish support the suggestion that, in starvation, ketone bodies, but not non-esterified fatty acids, are an important fuel for muscle in elasmobranchs, whereas non-esterified fatty acids, but not ketone bodies, are an important fuel in teleosts. The results are discussed in relation to the evolution of a discrete lipid-storing adipose tissue in teleosts and higher vertebrates.
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PMID:Activities of enzymes of fat and ketone-body metabolism and effects of starvation on blood concentrations of glucose and fat fuels in teleost and elasmobranch fish. 53 30

Clofibrate was administered in the diet (0.3% w/w) for varying periods of time to normal rats. Rats were killed by decapitation and several biochemical measurements were made. Clofibrate lowered serum levels of cholesterol and triglyceride and produced a kidney hypertrophy; these effects were maximal after 3 days of feeding and persisted for 21 days. Serum clofibric acid levels were highest on the 3rd day and decreased to maintenance levels by the 7th day. Clofibrate markedly increased the activities of glucose 6-phosphatase, pyruvate carboxylase and phosphoenolpyruvate carboxykinase in kidney cortex and the synthesis of glucose from glutamate, lactate, pyruvate, glycerol and malate by kidney cortex slices. Clofibrate treatment did not affect blood pH or bicarbonate levels. It is concluded that clofibrate enhances renal gluconeogenesis in the rat and that the effect is not caused by altering acid-base balance.
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PMID:Renal gluconeogenesis in clofibrate-treated rats. 63 72

Administering 3-aminopicolinate to rats starved for 24h immediately initiated a progressive increase in blood glucose concentration. Hyperglycaemia was not the result of glycogenolysis, nor was it due to an inhibition of insulin release, since it caused marked hyperinsulinaemia. The rate of [6-(3)H]glucose disappearance from the blood of the intact rat was not altered by 3-aminopicolinate, indicating that it does not cause hyperglycaemia by inhibiting glucose utilization or by causing a redistribution of total body glucose. 3-Aminopicolinate increased the rate of fall in the specific radioactivity of blood [6-(3)H]-glucose, indicating dilution of the glucose pool by newly synthesized glucose. The rate of (14)C incorporation into blood glucose from [(14)C]alanine and [(14)C]lactate was increased 90 and 35% respectively, whereas that from [(14)C]glycerol and [(14)C]xylitol was either unaffected or slightly decreased by 3-aminopicolinate administration. Liver phosphoenolpyruvate of rats was increased to four to seven times the normal concentration 10min to 1h after injections of 50-300mg of 3-aminopicolinate/kg body wt. and the amounts of 2-phosphoglycerate and 3-phosphoglycerate were increased to three to four times normal. The high concentrations of liver phosphoenolpyruvate, 2-phosphoglycerate and 3-phosphoglycerate, as well as the enhancement of gluconeogenesis from lactate and alanine, but not from glycerol or xylitol, is compatible with an enhancement of gluconeogenesis at a step between pyruvate and the triose phosphates. After injections of 3-aminopicolinate, liver malate, citrate, aspartate, alanine, lactate and pyruvate were also increased, but to lesser extents than was phosphoenolpyruvate. The increases in some of these metabolites were approximated after an intravenous infusion of glucose, so their elevated concentration after 3-aminopicolinate administration could have been, in part, a consequence of the hyperglycaemia. The possibility is considered that 3-aminopicolinate stimulates gluconeogenesis in vivo by facilitating Fe(2+) activation of phosphoenolpyruvate carboxykinase as it does with the purified enzyme in vitro [MacDonald & Lardy (1978) J. Biol. Chem.253, 2300-2307]. In this effect 3-aminopicolinate may simulate the physiological role of the naturally occurring ferroactivator protein [Bentle & Lardy (1977) J. Biol. Chem.252, 1431-1440].
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PMID:Hyperglycaemic activity and metabolic effects of 3-aminopicolinic acid. 74 55

1. Tryptophan inhibition of gluconeogenesis in isolated rat liver cells is characterized by a 20 min lag period before linear rates of glucose output are attained. 2. Half-maximal inhibition of gluconeogenesis in isolated rat hepatocytes is produced by approx. 0.1 mM-tryptophan. 3. Tryptophan inhibits gluconeogenesis from all substrates giving rise to oxaloacetate, but stimulates glycerol-fuelled glucose production. 4. Gluconeogenesis in guinea-pig hepatocytes is insensitive to tryptophan. 5. Changes in metabolite concentrations in rat liver cells are consistent with a locus of inhibition at the step catalysed by phosphoenolpyruvate carboxykinase. 6. Inhibition of gluconeogenesis persists in cells from rats pretreated with tryptophan in vivo. 7. Tryptophan has no effect on urea production from alanine, but decreases [1-14C]palmitate oxidation to 14CO2 and is associated with an increased [hydroxybutyrate]/[acetoacetate] ratio. 8. These results are discussed with reference to the control of gluconeogenesis in various species.
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PMID:Differential effects of tryptophan on glucose synthesis in rats and guinea pigs. 74 54

A detailed model of intermediary metabolism has been constructed which is consistent with all known information on the compartmental structure of metabolism in Tetrahymena, on the enzyme complement of this cell, and on the localization of the enzymes. The model allows computation of the specific activity of every carbon atom of all metabolites and thus of the flux of carbon along the major pathways of metabolism under steady state conditions. To test the model, data were required from cells grown under standard conditions and then suspended in a dilute salt solution and incubated for 1 hour in a mixture of acetate, pyruvate, hexanoate, bicarbonate, and glutamate labeled in a total of 10 positions, but with only one substrate labeled in any given flask. Twenty-seven measurements of label incorporation into CO2, lipids, glycogen, glutamate, and alanine were made, plus measurements of label distribution into fatty acid and glycerol moieties for 4 of the substrates and of oxygen consumption and of glycogenolysis, yielding 33 independent measurements. These, plus about 18 "limit" measurements which also constrain any possible solutions, were in sufficient excess of the 23 independent parameters to permit a stringent assessment of the model. Equations derived directly from the structure of the model and from the known stereochemistry of the reactions were programmed on a PDP-15 computer and values of the Qo2 and of label expected to be incorporated into the various products actually measured were computed for any given set of flux rates. A set of flux rates was found which yielded an excellent fit to the observed data. The ability to achieve a fit to the data for an overdetermined system constitutes strong support for this structural model of intermediary metabolism and the computed flux rates therefore provide a quantitative description of metabolite flow in the intact cell. Despite the redundancy of measurements relative to parameters to be determined, it was not possible to define a unique set of values for the flux through phosphoenolpyruvate carboxylase and phosphoenolpyruvate carboxykinase, although the relationship between these fluxes is specified by the model. The analysis allows estimation of the recycling of phosphoenopyruvate through pyruvate kinase under conditions of net glyconeogenesis and an apparently futile exchange of acetyl-CoA between the inner and outer mitochondrial compartments. Carbon flow through the glyoxylate bypass under these conditions is about one-third of that through the Krebs cycle. The analysis also shows a net transport of malate from the peroxisomes to the mitochondria, consistent with the anaplerotic role of the peroxisomal glyoxylate bypass in Tetrahymena.
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PMID:A quantitative analysis of metabolite fluxes along some of the pathways of intermediary metabolism in Tetrahymena pyriformis. 80 76


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