scholarly journals The effect of treatment of the rat with bacterial endotoxin on gluconeogenesis and pyruvate metabolism in subsequently isolated hepatocytes

1993 ◽  
Vol 289 (1) ◽  
pp. 169-172 ◽  
Author(s):  
C G Jones ◽  
M A Titheradge
Keyword(s):  
Pyruvate Kinase ◽  
Pyruvate Carboxylase ◽  
Phosphoenolpyruvate Carboxykinase ◽  
Feedback Inhibition ◽  
Isolated Hepatocytes ◽  
Bacterial Endotoxin ◽  
Pyruvate Metabolism ◽  
Pyruvate Kinase Activity ◽  
Glucose Synthesis ◽  
Effect Of Treatment

The effect of treatment of rats with bacterial endotoxin on gluconeogenesis and the flux through pyruvate kinase, phosphoenolpyruvate carboxykinase (PEPCK), pyruvate carboxylase and pyruvate dehydrogenase (PDH) was measured in isolated hepatocytes, prepared from animals starved for 18 h, incubated in the presence of 1 mM pyruvate. The lipopolysaccharide reduced gluconeogenesis by 50% and lowered the flux through pyruvate kinase, PEPCK and pyruvate carboxylase by comparable amounts. There was no effect of endotoxaemia on PDH flux, indicating that the lowered rate of gluconeogenesis is not the result of a redistribution of pyruvate metabolism between oxidation and carboxylation. The results confirm that a stimulation of pyruvate kinase activity following treatment with lipopolysaccharide is not involved in the inhibition of gluconeogenesis, but that the effect resides at the level of phosphoenolpyruvate formation. The most favoured mechanism for the inhibition of glucose synthesis is via an inhibition of PEPCK and subsequent feedback inhibition of pyruvate carboxylase, although a secondary effect at the level of the mitochondria and pyruvate carboxylase cannot be excluded.

scholarly journals Effect of dexamethasone on gluconeogenesis, pyruvate kinase, pyruvate carboxylase and pyruvate dehydrogenase flux in isolated hepatocytes

1993 ◽  
Vol 289 (3) ◽  
pp. 821-828 ◽  
Author(s):  
C G Jones ◽  
S K Hothi ◽  
M A Titheradge
Keyword(s):  
Pyruvate Kinase ◽  
Pyruvate Dehydrogenase ◽  
Pyruvate Carboxylase ◽  
Phosphoenolpyruvate Carboxykinase ◽  
Tricarboxylic Acid Cycle ◽  
Acute Effect ◽  
Isolated Hepatocytes ◽  
Pyruvate Oxidation ◽  
Parallel Increase ◽  
Glucose Output

Treatment of 18 h-starved rats with dexamethasone and subsequent isolation and incubation of the hepatocytes in the presence of the steroid increased gluconeogenic flux with both 1.0 mM pyruvate and 1.0 mM lactate plus 0.2 mM pyruvate as the substrate. The magnitude of stimulation was comparable with both substrates. The increase in glucose output was accompanied by an increased flux through pyruvate carboxylase, although the absolute flux and magnitude were considerably less in the presence of the more reduced substrate. The effect of the steroid on the flux through pyruvate dehydrogenase was substrate-dependent, an inhibition occurring with the more oxidized substrate. There was no effect of steroid treatment on [1-14C]lactate or pyruvate oxidation or on tricarboxylic-acid-cycle flux as measured by [3-14C]pyruvate oxidation. Dexamethasone treatment resulted in a parallel increase in both pyruvate kinase flux and glucose synthesis with both substrates employed, indicating that the steroid had no effect on the partitioning of phosphoenolpyruvate between pyruvate and lactate formation and gluconeogenesis. Similarly there was no effect of the steroid on either the activity ratio or the total pyruvate kinase activity in the cells. It is suggested that the acute effect of the dexamethasone to increase gluconeogenesis resides at the level of phosphoenolpyruvate formation, i.e. pyruvate carboxylase and possibly phosphoenolpyruvate carboxykinase.

scholarly journals Effect of treatment of rats with dexamethasone in vivo on gluconeogenesis and metabolite compartmentation in subsequently isolated hepatocytes

1984 ◽  
Vol 219 (1) ◽  
pp. 117-123 ◽  
Author(s):  
E H Allan ◽  
M A Titheradge
Keyword(s):  
Pyruvate Carboxylase ◽  
Phosphoenolpyruvate Carboxykinase ◽  
Intact Cell ◽  
Isolated Hepatocytes ◽  
Dexamethasone Treatment ◽  
Acetyl Coa ◽  
General Activation ◽  
Effect Of Treatment ◽  
Stimulation Of

Hepatocytes prepared from rats treated with dexamethasone for 2 or 3h and maintained in the presence of 10 microM-dexamethasone in the preparation and incubation buffers showed significantly elevated rates of gluconeogenesis compared with those prepared from control animals. Dexamethasone treatment also increased the sensitivity of the cells to glucagon and the catecholamines. Analysis of the concentrations of metabolites in the gluconeogenic pathway indicated that dexamethasone decreased the intracellular concentration of pyruvate and increased those of phosphoenolpyruvate, acetyl-CoA and citrate, suggesting a stimulation of the reaction(s) converting pyruvate into phosphoenolpyruvate. This was substantiated by analysis of the pattern of metabolites found in the mitochondrial compartment after digitonin fractionation of the cells. Inclusion of 3-mercaptopicolinate in the incubation enhanced the effect of the hormone on the distribution of metabolites. Thus, in the absence of an effect of the steroid at the level of phosphoenolpyruvate carboxykinase or pyruvate kinase, dexamethasone treatment still increased the formation of malate, aspartate and citrate from pyruvate, indicating a stimulation in the intact cell of pyruvate carboxylase. It is suggested that the stimulation of pyruvate carboxylase is a result of a general activation of mitochondrial function, with an increase in the intramitochondrial concentrations of acetyl-CoA and ATP, a decrease in glutamate and an enhanced intramitochondrial [ATP]/[ADP] ratio.

scholarly journals Effect of treatment in vivo of rats with bacterial endotoxin on fructose 2,6-bisphosphate metabolism and L-pyruvate kinase activity and flux in isolated liver cells

1992 ◽  
Vol 284 (3) ◽  
pp. 761-766 ◽  
Author(s):  
E D Ceppi ◽  
R G Knowles ◽  
K M Carpenter ◽  
M A Titheradge
Keyword(s):  
Pyruvate Kinase ◽  
Intact Cell ◽  
Total Activity ◽  
Liver Cells ◽  
Bacterial Endotoxin ◽  
Phosphorylation State ◽  
Isolated Liver Cells ◽  
Effect Of Treatment ◽  
Isolated Liver ◽  
Stimulation Of

The effect of treatment of rats with bacterial endotoxin on fructose 2,6-bisphosphate (Fru-2,6-P2) metabolism was investigated in isolated liver cells prepared from 18 h-starved animals. The results obtained support the hypothesis that a stimulation of 6-phosphofructo-1-kinase (PFK-1) activity and an inhibition of fructose-1,6-bisphosphatase (Fru-1,6-P2ase) may be one mechanism underlying the inhibition of gluconeogenesis from lactate and pyruvate by endotoxin. We suggest that the stimulation of PFK-1 and inhibition of Fru-1,6-P2ase activity is the result of a 2-3-fold increase in Fru-2,6-P2. The latter is not due to changes in the total activity or phosphorylation state of the bifunctional 6-phosphofructo-2-kinase (PFK-2)/fructose-2,6-bisphosphatase, but appears to be the result of a decrease in the cytosolic concentration of phosphoenolpyruvate (PEP), an inhibitor of PFK-2 activity. The effect of endotoxin is resistant to the presence of glucagon, which has comparable effects in cells prepared from both control and endotoxin-treated animals. The mechanism by which endotoxin treatment of the rat decreases PEP and gluconeogenesis remains to be established. However, it does not involve alterations in either the total activity or the phosphorylation state of pyruvate kinase, nor does it involve increased flux through this enzyme in the intact cell, which is in fact decreased in this model of septic shock. It is suggested that the decreased flux may result from a lower rate of formation of PEP, suggesting that the prime lesion in sepsis is an inhibition of one or more of the steps leading to PEP formation.

scholarly journals Is the adenine nucleotide translocator rate-limiting for oxidative phosphorylation?

1978 ◽  
Vol 172 (2) ◽  
pp. 333-342 ◽  
Author(s):  
Marion Stubbs ◽  
Pierre V. Vignais ◽  
Hans A. Krebs
Keyword(s):  
Phosphoenolpyruvate Carboxykinase ◽  
Adenine Nucleotide ◽  
Phosphoglycerate Kinase ◽  
Isolated Hepatocytes ◽  
Urea Synthesis ◽  
Intermediary Metabolites ◽  
Glucose Synthesis ◽  
High Concentrations ◽  
K Concentration ◽  
Rate Limiting

1. The effects of atractyloside and carboxyatractyloside (between 5 and 40μm) on O2 uptake, glucose synthesis, urea synthesis, the adenine nucleotide content and the intracellular K+ concentration were measured in isolated hepatocytes. 2. Urea synthesis was much less inhibited than glucose synthesis by both atractylosides. Measurements of intermediary metabolites of carbohydrate metabolism in freeze-clamped liver after injection of atractyloside into rats indicate that inhibition of gluconeogenesis is due to interference at the cytosolic reactions requiring ATP (phosphoenolpyruvate carboxykinase and 3-phosphoglycerate kinase). 3. The decrease in [ATP]/[ADP]×[Pi] after addition of atractyloside or carboxyatractyloside was restricted to the cytosol. 4. Dihydroxyacetone can be converted either into glucose with the consumption of 2mol of ATP (per mol of glucose) or into lactate with the production of 2mol of ATP. In the presence of high concentrations of atractyloside and carboxyatractyloside more ATP was produced than was used for the synthesis of glucose from dihydroxyacetone, probably for the maintenance of intracellular [K+]. 5. When the rates of respiration were altered by changing substrates, the degrees of inhibition of respiration and translocation by a given concentration of the atractylosides were the same, whereas at a given concentration of HCN the degree of inhibition was high at higher initial rates, and low at lower initial rates. 6. Inhibition of a complex series of reactions by atractyloside does not necessarily indicate that the translocator is a rate-limiting step in that sequence as Th. P. M. Akerboom, H. Bookelman & J. M. Tager [(1977) FEBS. Lett.74, 50–54] assume. This point is discussed.

scholarly journals Metabolic control of hepatic gluconeogenesis during exercise

1983 ◽  
Vol 212 (3) ◽  
pp. 633-639 ◽  
Author(s):  
G L Dohm ◽  
E A Newsholme
Keyword(s):  
Metabolic Control ◽  
Pyruvate Kinase ◽  
Pyruvate Carboxylase ◽  
Phosphoenolpyruvate Carboxykinase ◽  
Prolonged Exercise ◽  
Allosteric Effectors ◽  
Fructose 1,6 Bisphosphatase ◽  
Metabolite Concentrations ◽  
Fructose 1,6 Bisphosphate ◽  
Hexose Phosphates

Prolonged exercise increased the concentrations of the hexose phosphates and phosphoenolpyruvate and depressed those of fructose 1,6-bisphosphate, triose phosphates and pyruvate in the liver of the rat. Since exercise increases gluconeogenic flux, these changes in metabolite concentrations suggest that metabolic control is exerted, at least, at the fructose 6-phosphate/fructose 1,6-bisphosphate and phosphoenolpyruvate/pyruvate substrate cycles. Exercise increased the maximal activities of glucose 6-phosphatase, fructose 1,6-bisphosphatase, pyruvate kinase and pyruvate carboxylase in the liver, but there were no changes in those of glucokinase, 6-phosphofructokinase and phosphoenolpyruvate carboxykinase. Exercise changed the concentrations of several allosteric effectors of the glycolytic or gluconeogenic enzymes in liver; the concentrations of acetyl-CoA, ADP and AMP were increased, whereas those of ATP, fructose 1,6-bisphosphate and fructose 2,6-bisphosphate were decreased. The effect of exercise on the phosphorylation-dephosphorylation state of pyruvate kinase was investigated by measuring the activities under conditions of saturating and subsaturating concentrations of substrate. The submaximal activity of pyruvate kinase (0.5 mM-phosphoenolpyruvate), expressed as percentage of Vmax., decreased in the exercised animals to less than half that found in the controls. These changes suggest that hepatic pyruvate kinase is less active during exercise, possibly owing to phosphorylation of the enzyme, and this may play a role in increasing the rate of gluconeogenesis.

scholarly journals The effect of fructose on pyruvate kinase activity in isolated hepatocytes. Inhibition by allantoin and alanine

1982 ◽  
Vol 208 (1) ◽  
pp. 171-178 ◽  
Author(s):  
S M Mapungwana ◽  
D R Davies
Keyword(s):  
Uric Acid ◽  
Pyruvate Kinase ◽  
Kinase Activity ◽  
Isolated Hepatocytes ◽  
Pyruvate Kinase Activity ◽  
Crude Extracts

1. Incubation of isolated hepatocytes with fructose at concentrations above 3 mM resulted in an apparent inhibition of pyruvate kinase assayed in crude extracts at sub-optimal phosphoenolpyruvate concentrations. 2. Fructose at concentrations below 3 mM caused an activation of the enzyme. 3. Increases in the hepatocyte contents of the positive effectors fructose 1.6-bisphosphate and fructose 1-phosphate were found at all concentrations of fructose up to 10mM. 4. Removal of the extrahepatocyte medium from the hepatocytes by washing resulted in an activation of the enzyme at all concentrations of fructose examined. 5. Inhibitors of the enzyme were shown to accumulate in the hepatocytes despite the depletion of ATP (a known negative effector) caused by higher concentrations of fructose. Indeed the inhibition of pyruvate kinase appeared to be correlated to the depletion of ATP. 6. Alanine (a known inhibitor) was shown to accumulate in hepatocytes as a consequence of incubation with fructose. 7. Allantoin and uric acid were shown to be inhibitors of a partially purified pyruvate kinase preparation assayed both in the presence and in the absence of fructose 1.6-bisphosphate. 8. Allantoin, but not uric acid, accumulated in the extrahepatocyte medium as a result of incubation of the cells with 10 mM-fructose.

scholarly journals Phosphoenolpyruvate Carboxykinase as the Sole Anaplerotic Enzyme in Saccharomyces cerevisiae

2010 ◽  
Vol 76 (16) ◽  
pp. 5383-5389 ◽  
Author(s):  
Rintze M. Zelle ◽  
Josh Trueheart ◽  
Jacob C. Harrison ◽  
Jack T. Pronk ◽  
Antonius J. A. van Maris
Keyword(s):  
Saccharomyces Cerevisiae ◽  
Carbon Source ◽  
Pyruvate Kinase ◽  
Pyruvate Carboxylase ◽  
Sole Carbon Source ◽  
Phosphoenolpyruvate Carboxykinase ◽  
Single Point ◽  
Point Mutations ◽  
Equilibrium Analysis ◽  
Evolutionary Engineering

ABSTRACT Pyruvate carboxylase is the sole anaplerotic enzyme in glucose-grown cultures of wild-type Saccharomyces cerevisiae. Pyruvate carboxylase-negative (Pyc−) S. cerevisiae strains cannot grow on glucose unless media are supplemented with C4 compounds, such as aspartic acid. In several succinate-producing prokaryotes, phosphoenolpyruvate carboxykinase (PEPCK) fulfills this anaplerotic role. However, the S. cerevisiae PEPCK encoded by PCK1 is repressed by glucose and is considered to have a purely decarboxylating and gluconeogenic function. This study investigates whether and under which conditions PEPCK can replace the anaplerotic function of pyruvate carboxylase in S. cerevisiae. Pyc− S. cerevisiae strains constitutively overexpressing the PEPCK either from S. cerevisiae or from Actinobacillus succinogenes did not grow on glucose as the sole carbon source. However, evolutionary engineering yielded mutants able to grow on glucose as the sole carbon source at a maximum specific growth rate of ca. 0.14 h−1, one-half that of the (pyruvate carboxylase-positive) reference strain grown under the same conditions. Growth was dependent on high carbon dioxide concentrations, indicating that the reaction catalyzed by PEPCK operates near thermodynamic equilibrium. Analysis and reverse engineering of two independently evolved strains showed that single point mutations in pyruvate kinase, which competes with PEPCK for phosphoenolpyruvate, were sufficient to enable the use of PEPCK as the sole anaplerotic enzyme. The PEPCK reaction produces one ATP per carboxylation event, whereas the original route through pyruvate kinase and pyruvate carboxylase is ATP neutral. This increased ATP yield may prove crucial for engineering of efficient and low-cost anaerobic production of C4 dicarboxylic acids in S. cerevisiae.

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