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PubMed1990

Persistence of gluconeogenesis in Escherichia coli poisoned by oxidant stress.

The poisoning (inhibition of growth rate) of Escherichia coli by 4.2 atmospheres of hyperbaric oxygen was less when the culture energy source was glucose, fructose-6-phosphate, or glycerol, compared to pyruvate, oxaloacetate, or amino acids. This was consistent with previous indirect data which pointed to impaired gluconeogenesis in the toxicity mechanism. However, the three enzymes unique to gluconeogenesis (fructose-1, 6-diphosphatase, phosphoenolpyruvate synthase and phosphoenolpyruvate carboxyl-kinase) were not decreased in specific activity to a biologically significant extent in cell-free extract of cells poisoned by hyperbaric oxygen. Net glycogen synthesis in vivo was not decreased from glycerol, pyruvate or oxaloacetate, compared to glucose in cells exposed to oxidant stress from hyperbaric oxygen or 1 mM aerobic paraquat with cells exposed as exponentially growing cells prior to assay or as resting cells during the assay.

Air Pressure↗
PubMedDate not supplied

[Qualitative study of a mathematical model of the open futile cycle fructose-6-P--fructose-1,6-P2].

A simple mathematical model of the open futile cycle fructose-6-P in equilibrium fructose-1,6-P2 in which the fructose bisphosphatase reaction is inhibited by excess of its substrate has been analysed. A detailed qualitative investigation of the model shows that it possesses all properties characteristic of any other dynamical system of the second order which has a hysteretic major null-cline, 1 to 3 steady states and is capable of generating self-oscillations.

Chemical Phenomena↗
PubMed1979

Contribution of cyclic adenosine 3':5'-monophosphate to the regulation of bacterial glycogen synthesis in vivo. Effect of carbon source and cyclic adenosine 3':5'-monophosphate on the quantitative relationship between the rate of glycogen synthesis and the cellular concentrations of glucose 6-phosphate and fructose 1,6-diphosphate in Escherichia coli.

When either fructose, glycerol, or succinate served as a sole source of carbon and energy in nitrogen-starved cultures of Escherichia coli W4597(K) the values of the kinetic constants of the equation that expresses the relationship between glycogen synthesis and hexose phosphates were different from the values observed when glucose was the sole source of carbon and energy. Addition of glucose during either exponential growth or nitrogen starvation to a culture using one of the other carbon sources slowed the rate of glycogen synthesis and shifted the values of the constants toward the values observed in cultures using glucose alone. Addition of cyclic AMP (cyclic adenosine 3':5'-monophosphate) during exponential growth of a culture using glucose caused the values of the constants to be shifted toward the values observed in cultures using a carbon source other than glucose. In all of the metabolic conditions studied in this report the adenylate energy charge ((ATP + 1/2 ADP)/(ATP + ADP + AMP)) and the level of the rate-limiting enzyme of glycogen synthesis, ADP-glucose synthetase (glucose 1-phosphate adenylyltransferase, EC 2.7.7.27), were the same. The data presented here indicate that the difference we observed in the quantitative relationship for glycogen synthesis is the result of the different cellular levels of cyclic AMP in the cells using glucose and the cells using one of the other carbon sources. Since cyclic AMP does not affect the velocity of ADP-glucose synthetase in vitro, apparently a change in the cellular level of cyclic AMP causes a shift in the cellular level of a presently unknown (and previously undetected) effector of this enzyme. The shift in the level of this effector evidently alters the response of the enzyme in vivo to the substrate glucose 1-phosphate and the activator fructose 1,6-diphosphate.

Adenine Nucleotides↗
PubMed1990

Purification and properties of pyruvate kinase from Dictyostelium discoideum.

Pyruvate kinase (EC 2.7.1.40) from aggregating Dictyostelium discoideum cells has been purified to homogeneity. It has a monomeric molecular weight of 66kD and is tetrameric in low ionic strength buffers. The enzyme is not regulated by fructose 1,6-bisphosphate or by alanine and appears to resemble the M1 isoenzyme from rat liver most closely, although its activity is not inhibited by ATP.

Dictyostelium↗
PubMed1990

Oscillatory synthesis of glucose 1,6-bisphosphate and frequency modulation of glycolytic oscillations in skeletal muscle extracts.

Oscillatory behavior of glycolysis in cell-free extracts of rat skeletal muscle involves bursts of phosphofructokinase activity, due to autocatalytic activation by fructose-1,6-P2. Glucose-1,6-P2 similarly might activate phosphofructokinase in an autocatalytic manner, because it is produced in a side reaction of phosphofructokinase and in a side reaction of phosphoglucomutase using fructose-1,6-P2. When muscle extracts were provided with 1 mM ATP and 10 mM glucose, glucose-1,6-P2 accumulated in a stepwise, but monotonic, manner to 0.7 microM in 1 h. The stepwise increases occurred during the phases when fructose-1,6-P2 was available, consistent with glucose-1,6-P2 synthesis in the phosphoglucomutase side reaction. Addition of 5-20 microM glucose-1,6-P2 increased the frequency of the oscillations in a dose-dependent manner and progressively shortened the time interval before the first burst of phosphofructokinase activity. Addition of 30 microM glucose-1,6-P2 blocked the oscillations. The peak values of the [ATP]/[ADP] ratio were then eliminated, and the average [ATP]/[ADP] ratio was reduced by half. In the presence of higher, near physiological concentrations of ATP and citrate (which reduce the activation of phosphofructokinase by glucose-1,6-P2), high physiological concentrations of glucose-1,6-P2 (50-100 microM) increased the frequency of the oscillations and did not block them. We conclude that autocatalytic activation of phosphofructokinase by fructose-1,6-P2, but not by glucose-1,6-P2, is the mechanism generating the oscillations in muscle extracts. Glucose-1,6-P2 may nevertheless play a role in facilitating the initiation of the oscillations and in modulating their frequency.

Adenine Nucleotides↗
PubMed1990

Effect of fructose 1,6-diphosphate infusion on the hormonal response to exercise.

Exogenous fructose 1,6-diphosphate (FDP), a glycolytic intermediate, has recently been demonstrated to accelerate ATP production, prevent glycogen breakdown, stimulate glycogen synthesis, and synthesize free fatty acids in animals and humans. To assess the effects of FDP on the hormonal and metabolic response to exercise, ten trained males (34 +/- 7 yr) underwent 1 h of continuous exercise at 70% VO2max followed by 20 W.min-1 increments to exhaustion. Two hundred fifty mg.kg-1 body weight FDP or placebo was infused in randomized, double-blind, crossover fashion. No differences were observed in heart rate, blood pressure, gas exchange data, perceived effort, or glucose, insulin, free fatty acid, lactate, beta-hydroxybutyrate, glycerol, and glucagon concentration at rest, during exercise, or upon exhaustion. In contrast to the previously reported bioenergetic effects of FDP under conditions in which glycolysis is impeded (acidosis, hypoxia, and ischemia), FDP did not affect the gas exchange, hormonal, or substrate response to moderately high intensity exercise in healthy normals.

Adult↗
PubMed1987

A novel type of phosphofructokinase from plants.

A phosphofructokinase (PFK) has been purified to homogeneity from carrot roots as a large aggregated form (molecular weight greater than 5 million). The purified plant PFK, seemingly the cytosolic form, differed from its mammalian counterpart in a lower subunit molecular weight (60,000 verses 80,000), in being only sluggishly activated by fructose-2,6-bisphosphate, and in immunological properties. Similar to liver PFK, the purified carrot PFK could be dissociated by addition of 5 mM ATP to small and intermediate forms (respective molecular mass values of 2.4 X 10(5) and 6 X 10(5) Da). These small and intermediate forms could partially reassociate to the original large form in the presence of 5 mM Fru-6-P. Alkaline pH also effected the dissociation of the large and intermediate forms to the small form of PFK. All forms were present in significant amounts in freshly prepared carrot root extracts. The different forms of PFK showed characteristic pH activity profiles with pH optima of 8.6 (small form), 5.5 and 9.0 (intermediate form), and 7.0 and 8.5 (large forms). As alkaline pH (greater than or equal to approximately 8.5) dissociated the large and intermediate enzyme forms to yield the small form, it was concluded the "true" pH optima of the intermediate and large forms are pH 5.5 and 7.0, respectively. The pH optimum displayed by the intermediate and large forms in the alkaline region (pH 8.5-9.0) was considered to be due to their dissociation during assay. The different forms of PFK also had dissimilar regulatory properties, each showing a characteristic response to ATP, citrate, and Pi, but all were sensitive to inhibition by phosphoenolpyruvate and NADPH. Leaf cytosolic PFK, partially purified from spinach, showed similar properties. The results suggest that metabolite-dependent aggregation-disaggregation is a mechanism whereby plants regulate the activity of cytosolic PFK and the accompanying rate of glycolytic carbon flux.

Adenosine Triphosphate↗
PubMed1989

Age-linked alterations in fructose-2,6-bisphosphate-induced modulation of rat muscle phosphofructokinase.

Native muscle phosphofructokinase (PFK: EC 2.7.1.11) isolated from 25- and 100-week-old rats was subjected to in vitro studies on fructose-2,6-bisphosphate-induced alterations in the regulatory roles of other key metabolic modulators of this enzyme. Although fructose 2,6-bisphosphate-mediated reversal of citrate inhibition did not show any age-related difference, synergism with glucose-1,6-bisphosphate effect was found to be slightly increased with the enzyme of 100-week-old rats. In addition, apart from a significant decrease in the extent of fructose-2,6-bisphosphate activation, synergism with AMP activation and reversal of ATP and pyridoxal-5-phosphate inhibitions were observed to be decreased markedly with the enzyme of 100-week-old rats in comparison with that of 25-week-old rats. Such age-dependent alterations in muscle PFK provide evidence for conformational modification in this enzyme as a function of age.

Adenosine Monophosphate↗
PubMed1989

Fructose 2,6-bisphosphate and trehalose metabolism in Saccharomyces cerevisiae.

1. A regulatory mutant of Saccharomyces (fdp) unable to activate fructose 1,6-bisphosphatase presented a normal response to the glucose and fructose signals as measured by trehalase activation, indicating that the inability of the strain to grow on these sugars is caused by a defect located beyond membrane interactions. 2. In vivo experiments with a mutant strain bearing a phosphoglucoisomerase gene (pgil-delta) deletion showed that activation of trehalase and deactivation of the tehalose-6-phosphate synthase complex occurred to the same extent whether glucose or fructose was used as signal. 3. These results suggest that fructose-2,6-bisphosphate is not involved in the interconversion of forms of the enzymes of trehalose metabolism. Furthermore, when fructose-2,6-bisphosphate was assayed on trehalose synthesizing activity using cell-free extracts and partially purified preparations of the complex, no effect was observed. 4. We conclude that regulation by cAMP fulfills the requirements for control of trehalose levels in Saccharomyces.

Cyclic AMP↗
PubMed1989

[Fructose-2,6-diphosphate and glycolysis of tumor cells].

Tumour and proliferative cells maintain a high glycolytic rate even under aerobic conditions. The discovery of fructose-2,6-bisphosphate, a potent stimulator of glycolysis, has prompted a re-investigation of this phenomenon. Rat hepatoma cells and fibroblasts stimulated by mitogens or transformed by the Rous sarcoma virus, were used as models. The results indicate that the stimulation of glycolysis induced by these agents can be explained by an increase in the concentration of fructose-2,6-bisphosphate and in the activity of the enzyme synthesizing it.

Animals↗
PubMed1989

[Effect of fructose-1,6-diphosphate on the size of the necrotic area and course of the acute period of experimental myocardial infarction in rats].

The experiments on rats indicated that fructose-1,6-diphosphate substantially decreased the sizes of a necrotic zone, elevated myocardial ATP levels, reduced the edematization of lung tissue, shortened the duration of early postocclusive arrhythmias, and increased the latent period for their development. A dose-dependent cardioprotective effect was found in the preparation.

Adenosine Triphosphate↗
PubMed1989

[Effects of fructose-1,6-diphosphate in patients with chronic ischemic heart disease. Echocardiographic study].

The effects of fructose-1,6-diphosphate (FDP) on cardiac activity were studied in 20 patients with chronic ischemic heart disease. Each patient received intravenously, in two different days, a single dose of FDP 20 g and placebo, according to a cross-over study design. Immediately prior to and ten minutes following each dosing, patients underwent an echocardiographic assessment. The comparison of pre- and post-treatment readings indicates that the diasto-systolic difference of left ventricular dimension increased by 10% after FDP (p less than 0.01). Similarly the increment of interventricular septum thickness increased by 16% (p less than 0.01) and that of posterior left ventricular wall thickness by 19% (p less than 0.01). In contrast the changes recorded after placebo treatment were far from being significant. These data indicate that the acute administration of a single dose of FDP may improve the cardiac performance in patients with chronic ischemic heart disease.

Adult↗
PubMed1989

Conformation of NAD+ bound to allosteric L-lactate dehydrogenase activated by chemical modification.

On modification of arginine residues with 2,3-butanedione, the Thermus caldophilus L-lactate dehydrogenase is converted to an activated form that is independent of an allosteric effector, fructose 1,6-bisphosphate (Fru-1,6-P2). The conformation of NAD+ bound to the modified enzyme in the absence of Fru-1,6-P2 was investigated by means of proton NMR, analyzing the time dependence of the transferred nuclear Overhauser effect (TRNOE) and TRNOE action spectra. The inter-proton distances determined on TRNOE analysis indicated that both the nicotinamide riboside moiety and the adenosine moiety of NAD+ were in the anti conformation, the ribose rings being in the C3'-endo form. This conformation was almost the same as that of NAD+ bound to the native enzyme-Fru-1,6-P2 complex, rather than that of NAD+ bound to the free native enzyme. These results suggest that the C3'-endo-anti form of the enzyme-bound NAD+ is essential for the activation of the T. caldophilus L-lactate dehydrogenase.

Allosteric Regulation↗