Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “Fructosediphosphates”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 1,315 records · Page 73Linked to original sources
PubMed1985

Inorganic phosphate amplifies the effects of AMP and fructose-2,6-bisphosphate on yeast phosphofructokinase.

Inorganic phosphate is an important regulator of yeast phosphofructokinase activity. In the absence of AMP and fructose-2,6-bisphosphate the dependence of enzyme activity on the concentration of inorganic phosphate is sigmoidal. AMP and fructose-2,6-bisphosphate increase the affinity of phosphofructokinase to inorganic phosphate. At low fructose-6-phosphate concentrations inorganic phosphate amplifies the activating effect of AMP and fructose-2,6-bisphosphate. Yeast phosphofructokinase is more sensitive to ATP inhibition in the absence of inorganic phosphate than in its presence. While in the absence of inorganic phosphate a definite ATP inhibition prevails even at high levels of AMP or fructose-2,6-bisphosphate, the ATP inhibition can be relieved by the cooperation of inorganic phosphate and fructose-2,6-bisphosphate. These effects of inorganic phosphate provide an explanation for the stimulation of glycolysis under anaerobic conditions by inorganic phosphate at unchanged concentrations of AMP and fructose-2,6-bisphosphate (Lagunas and Gancedo, Eur. J. Biochem. 137, 479-483 (1983)).

Adenosine Monophosphate↗
PubMed1986

Kinetic effects of fructose-1,6-bisphosphate on yeast phosphofructokinase.

Yeast phosphofructokinase is known to be effectively activated by fructose-2,6-bisphosphate and AMP. In the absence of the two effectors, fructose-1,6-bisphosphate activates or inhibits the enzyme according to the concentrations of the substrates and of inorganic phosphate. At cellular concentrations of the substrates, however, the effects of fructose-1,6-bisphosphate are negligible. Whereas the activation of the enzyme by AMP is not affected by fructose-1,6-bisphosphate, the latter was found to diminish strongly the activity of the fructose-2,6-bisphosphate-activated enzyme. Inorganic phosphate amplifies the activating effect of fructose-2,6-bisphosphate and augments also the deactivation of the fructose-2,6-bisphosphate-activated enzyme. The deactivating action of fructose-1,6-bisphosphate with respect to fructose-2,6-bisphosphate dominates at low concentrations of fructose-6-phosphate and high levels of ATP and might be of regulatory significance.

Enzyme Activation↗
PubMed1987

Regulation of liver metabolism by enzyme phosphorylation during mammalian hibernation.

Kinetic properties of regulatory enzymes of glycolysis in liver of the mouse, Zapus hudsonius, were modified during hibernation, the probable mechanism being covalent modification. Liver glycogen phosphorylase activity was strongly depressed during both short (less than 24 h) and long (5-8 days) term hibernation, the mechanism involving a decrease in both the percentage of enzyme in the active a form and the total amount (a + b) of enzyme expressed. Phosphofructokinase showed kinetic changes (a 2.5-fold increase in Ka for fructose-2,6-P2, 4- and 3.7-fold decreases in I50 values for ATP and citrate, compared to euthermic controls) in liver of hibernators indicative of phosphorylation inactivation of the enzyme. Measured levels of fructose-2,6-P2 in liver did not change during hibernation. Changes in pyruvate kinase kinetics in liver from long term hibernators similarly indicated enzyme phosphorylation in the depressed state (Ka for fructose-1,6-P2 increased 4.4-fold, I50 for L-alanine decreased 6.3-fold). Apparent covalent modification of glycolytic enzymes during hibernation may serve two functions: depression of glycolytic activity as part of the general metabolic rate depression of hibernation, or reorganization of fuel use in the hibernating state to limit carbohydrate catabolism and promote gluconeogenesis.

Adenosine Triphosphate↗
PubMed1986

Binding of fructose-1,6-bisphosphate to yeast phosphofructokinase.

Binding of fructose-1,6-bisphosphate to yeast phosphofructokinase (EC 2.7.1.11) was measured in a concentration range of 5 to 200 microM of fructose-1,6-bisphosphate with the ultrafiltration technique. At saturation two molecules of fructose-1,6-bisphosphate are bound per subunit of the octameric enzyme. Two distinct types of binding sites have been observed. The high affinity sites (KH = 32.7 +/- 5 microM) exhibit a hyperbolic response in respect to the binding of fructose-1,6-bisphosphate, the low affinity sites (KL = 57.2 +/- 6 microM) show significant positive cooperativity.

Fructosediphosphates↗
PubMed1987

Control of phosphofructokinase by fructose 2,6-bisphosphate in B-lymphocytes and B-chronic lymphocytic leukemia cells.

The levels of fructose 2,6-bisphosphate and glucose 1,6-bisphosphate and the activities of the key glycolytic enzymes have been studied in T- and B-lymphocytes, and in B-chronic lymphocytic leukemia cells (B-CLL). In both kinds of cells these two bisphosphorylated metabolites have been identified and are present at similar concentrations. Their phosphofructokinase, like that of other normal or tumoral cells, is sensitive to these activators. Fructose 2,6-bisphosphate is the most potent stimulator; it displays the properties of a positive effector. It greatly increases the affinity for fructose 6-phosphate and relieves the inhibition by adenosine triphosphate, without changing Vmax. This effect is also synergistic with adenosine monophosphate. Despite few differences in the activity of phosphofructokinase and in the content of its main effectors in B-lymphocytes and in B-CLL cells, the kinetic properties of the enzyme from B-CLL cells were different, the enzyme being more sensitive to fructose 2,6-bisphosphate (Ka 2 orders of magnitude lower) and to glucose 1,6-bisphosphate than the enzyme from normal lymphocytes. The results reported showing that phosphofructokinase from B-CLL lymphocytes is altered in regulatory properties and the observed changes, in comparison to phosphofructokinase from normal B-lymphocytes, fit well with the hypothesis that fructose 2,6-bisphosphate can also assume a regulatory role in these cancer cells characterized by proliferation and accumulation of relatively mature-appearing lymphocytes.

B-Lymphocytes↗
PubMed1987

Regulation of adult and fetal myocardial phosphofructokinase. Relief of cooperativity and competition between fructose 2,6-bisphosphate, ATP, and citrate.

To clarify the physiological role of fructose 2,6-bisphosphate in the perinatal switching of myocardial fuels from carbohydrate to fatty acids, the kinetic effects of fructose 2,6-bisphosphate on phosphofructokinase purified from fetal and adult rat hearts were compared. For both enzymes at physiological pH and ATP concentrations, 1 microM fructose 2,6-bisphosphate induced a greater than 10-fold reduction in S0.5 for fructose 6-phosphate and it completely eliminated subunit cooperativity. Fructose 2,6-bisphosphate may thereby reduce the influence of changes in fructose 6-phosphate concentration on phosphofructokinase activity. Based on double-reciprocal plots and ATP inhibition studies, adult heart phosphofructokinase activity is more sensitive to physiological changes in ATP and citrate concentrations than to changes in fructose 2,6-bisphosphate concentrations. Fetal heart phosphofructokinase is less sensitive to ATP concentration above 5 mM and equally sensitive to citrate inhibition. The fetal enzyme has up to a 15-fold lower affinity for fructose 2,6-bisphosphate, rendering it more sensitive to changes in fructose 2,6-bisphosphate concentration than adult heart phosphofructokinase. Together, these factors allow greater phosphofructokinase activity in fetal heart while retaining sensitive metabolic control. In both fetal and adult heart, fructose 2,6-bisphosphate is primarily permissive: it abolishes subunit cooperativity and in its presence phosphofructokinase activity is extraordinarily sensitive to both the energy balance of the cell as reflected in ATP concentration and the availability of other fuels as reflected in cytosolic citrate concentration.

Adenosine Triphosphate↗
PubMed1987

Effects of insulin and work on fructose 2,6-bisphosphate content and phosphofructokinase activity in perfused rat hearts.

The effects of insulin and increased cardiac work on glycolytic rate, metabolite content, and fructose 2,6-bisphosphate (Fru-2,6-P2) content were studied in isolated perfused rat hearts. Steady-state rates of glycolysis increased 5-fold with the addition of insulin to the perfusate or by increasing cardiac pressure-volume work and correlated well in most conditions with changes in substrate concentration (Fru-6-P) and with concentration of the activator, Fru-2,6-P2. There was no correlation with changes in other well known regulators including citrate, ATP, AMP, Pi, or cytosolic phosphorylation potential. Using phosphofructokinase purified from hearts perfused under identical conditions, allosteric kinetic experiments were performed using the metabolite and effector concentrations determined from in vivo experiments. Reaction rates for phosphofructokinase calculated in vitro agreed well with the glycolytic rates measured in vivo and correlated with changes in Fru-6-P but not with other effectors. However, higher Fru-2,6-P2 levels were more effective in maintaining phosphofructokinase activity at high ATP and citrate levels. Kinetic experiments did not indicate a covalent modification of phosphofructokinase. These data indicate that control of cardiac phosphofructokinase and glycolysis may be accomplished by changes in the availability of substrate, Fru-6-P, and activator, Fru-2,6-P2, rather than by citrate, adenine nucleotides, or cytosolic phosphorylation potential as previously suggested.

Allosteric Regulation↗
PubMed1987

Fructose 2,6-bisphosphate and glucose 1,6-bisphosphate in avian and mammalian erythroid cells.

Chicken erythrocytes contain fructose 2,6-P2 at a concentration (0.6 nmol/10(9) cells) lower than that of glucose 1,6-P2 (5.4 nmol/10(9) cells) and similar to that of 2,3-bis phosphoglycerate (1.2 nmol/10(9) cells). In chick embryo erythrocytes the content of both bisphosphorylated hexoses is much lower. They begin to increase at hatching and reach chicken values in a few days. Fructose 2,6-P2 at microM concentration activates phosphofructokinase from chicken erythrocytes and releases the inhibition produced by ATP, 2,3-bisphosphoglycerate and inositol hexaphosphate. Glucose 1,6-P2 has similar effects but at much greater concentration. Rabbit reticulocytes contain fructose 2,6-P2 at a concentration (39 pmol/10(9) cells) much lower than that of glucose 1,6-P2 (74 nmol/10(9) cells).

2,3-Diphosphoglycerate↗
PubMed1987

Subunit composition, regulatory properties, and phosphorylation of phosphofructokinase from human gliomas.

In this study, we investigated the alterations in the activity, subunit profile, and kinetic regulatory properties of phosphofructokinase (PFK) from human gliomas compared with those from normal human brain. Gliomas showed a decrease in the enzyme activity as compared to normal brain. This decrease in PFK activity was accompanied by a relative increase in the expression of the liver type subunit of PFK. The enzymes from the tumor and normal brain showed no significant differences in their affinity toward the substrate fructose 6-phosphate. However, tumor and normal brain PFK showed major differences with respect to their behavior towards citrate and fructose 2,6-bisphosphate. The enzyme from the gliomas was less sensitive to citrate inhibition. More importantly, the enzyme from the tumor was more sensitive to the activation by fructose 2,6-bisphosphate. In addition, we found that in gliomas the L-type subunit could be phosphorylated, most probably by a cyclic AMP-independent protein kinase. This phosphorylation could not be detected in normal human brain. It is proposed that the preferential expression of the liver type subunit by undifferentiated cancer cells may be explained in terms of the unique regulatory properties of this isozyme.

Brain↗
PubMed1987

Increasing survival of dogs subjected to hemorrhagic shock by administration of fructose 1-6 diphosphate.

Previous reports from this laboratory described animal experiments in which intravenous administration of fructose 1-6 diphosphate (FDP) at the onset of hypovolemia, toxemia, and trauma effected improvement in hemodynamic and metabolic parameters, attenuation of tissue damage, and a significant increase in survival. The obvious question remained: Would this agent be as effective if administered after the onset of the shock syndrome? Thus 72 anesthetized dogs were subjected to normotensive hemorrhagic shock and were subsequently treated with FDP at 30 minutes, 1 hour, 90 minutes, and 2 hours after exsanguination. Analysis of the results (as compared with vehicle-treated controls) revealed evidence of improved cardiac output and arterial pressure (p less than 0.02), conservation of effective circulatory volume, better oxygen utilization, and a significant increase in survival (p less than 0.0001). These results, in conjunction with earlier experimental and recent clinical data, indicate that the therapeutic effect of FDP in ischemic and hypoperfusion states is in part metabolically mediated by the augmentation of carbohydrate utilization. Prevention of tissue injury is in part due to the inhibition of generation of oxygen-derived free radicals by neutrophils.

Animals↗
PubMed1988

Fructose 2,6-bisphosphate and 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. Fructose-2,6-P2 is an even more potent activator of phosphofructokinase and is competitive with fructose-1,6-P2 in binding and kinetic studies. The possible role and effects of fructose-2,6-P2 on the oscillating system were therefore examined. When muscle extracts were provided with 1 mM ATP and 10 mM glucose, fructose-2,6-P2 slowly accumulated to 50 nM in 1 h. The nearly monotonic rise, in contrast to the 50-fold oscillations in fructose-1,6-P2, indicated no involvement of fructose-2,6-P2 in the oscillatory process. Addition of 0.5 microM fructose-2,6-P2 blocked the oscillations, and there was negligible appearance of glycolytic intermediates from fructose-1,6-P2 to phosphoenolpyruvate, although similar amounts of lactate accumulated. In the presence of 0.2 microM fructose-2,6-P2, there were small, transient accumulations of fructose-1,6-P2, suggesting aborted activations of phosphofructokinase. Oscillations were not blocked by 0.1 microM fructose-2,6-P2. The average [ATP]/[ADP] ratio in the presence of 0.2 or 0.5 microM fructose-2,6-P2 was half the value in its absence, demonstrating the advantage of the oscillatory behavior in maintaining a high energy state. In the presence of higher, near physiological levels of ATP and citrate, inhibitors which reduce the affinity of phosphofructokinase for fructose-2,6-P2, glycolytic oscillations were not blocked by 1 microM fructose-2,6-P2, its approximate concentration in vivo.

Animals↗
PubMed1988

Binding of fructose 2,6-bisphosphate to yeast phosphofructokinase.

Binding of Fru-2,6-P2 to yeast phosphofructokinase was investigated by ultrafiltration technique. Per mol of subunit of phosphofructokinase (M = 100,000) 0.5 moles of Fru-2,6-P2 are bound. The binding curve proceeds cooperatively (nH = 1.8 +/- 0.2). The apparent affinity constant of Fru-2,6-P2 amounts to about 2.25 +/- 0.12 microM. Fru-1,6-P2 decreases the affinity of yeast phosphofructokinase to Fru-2,6-P2. The data can be described by assuming either competition of Fru-2,6-P2 and Fru-1,6-P2 for the same binding site or conformationally mediated interactions.

Fructosediphosphates↗
PubMed1988

Phosphofructokinase from bumblebee flight muscle. Molecular and catalytic properties and role of the enzyme in regulation of the fructose 6-phosphate/fructose 1,6-bisphosphate cycle.

Phosphofructokinase from the flight muscle of bumblebee was purified to homogeneity and its molecular and catalytic properties are presented. The kinetic behavior studies at pH 8.0 are consistent with random or compulsory-order ternary complex. At pH 7.4 the enzyme displays regulatory behavior with respect to both substrates, cooperativity toward fructose 6-phosphate, and inhibition by high concentration of ATP. Determinations of glycolytic intermediates in the flight muscle of insects exposed to low and normal temperatures showed statistically significant increases in the concentrations of AMP, fructose 2,6-bisphosphate, and glucose 6-phosphate during flight at 25 degrees C or rest at 5 degrees C. Measuring the activity of phosphofructokinase and fructose 1,6-bisphosphatase at 25 and 7.5 degrees C, in the presence of physiological concentrations of substrates and key effectors found in the muscle of bumblebee kept under different environmental temperatures and activity levels, suggests that the temperature dependence of fructose 6-phosphate/fructose 1,6-bisphosphate cycling may be regulated by fluctuation of fructose 2,6-bisphosphate concentration and changes in the affinity of both enzymes for substrates and effectors. Moreover, in the presence of in vivo concentrations of substrates, phosphofructokinase is inactive in the absence of fructose 2,6-bisphosphate.

Animals↗
PubMed1988

Tolbutamide enhances insulin action on gluconeogenesis and on fructose 2,6-bisphosphate levels in isolated rat hepatocytes.

In hepatocytes isolated from fed rats and incubated either under basal conditions or in the presence of glucagon, tolbutamide reduced gluconeogenesis from (U-14C) pyruvate by increasing the cellular concentration of fructose 2,6-bisphosphate. Furthermore, this sulfonylurea enhanced the inhibitory action of insulin on glucagon-stimulated gluconeogenesis; this effect was accompanied by a more marked increase of the cellular concentration of fructose 2,6-bisphosphate than that elicited by either insulin or the sulfonylurea alone. In connection with this, tolbutamide--without significant modification of cellular cyclic AMP levels--raised the proportion of 6-phosphofructo 2-kinase in active form in hepatocytes incubated either under basal conditions or in the presence of glucagon, and reinforced the action of insulin in antagonizing the glucagon-mediated inactivation of this enzyme.

Animals↗
PubMed1988

Improved left ventricular function after short-term treatment with fructose-1,6-diphosphate: echocardiographic study in chronic ischemic heart disease and idiopathic dilated cardiomyopathy.

The effect of fructose-1,6-diphosphate (FDP) on left ventricular function was assessed in seven patients with chronic ischemic heart disease and eight patients with idiopathic dilated cardiomyopathy. In a crossover study design each patient received 10 gm of FDP or saline placebo intravenously for three days. An M-mode echocardiographic assessment of left ventricular (LV) function was made before and after each treatment period. After FDP treatment, LV end-diastolic and systolic dimensions showed a 6% reduction (P less than 0.01), while peak lengthening rate of LV dimension in diastole and peak shortening rate of LV dimension in systole increased 17% and 10%, respectively (P less than 0.05). There was evidence that FDP was more effective in the patients with ischemic heart disease than in the patients with cardiomyopathy.

Aged↗
PubMed1985

Modulation of muscle phosphofructokinase at physiological concentration of enzyme.

Two approaches have been used to study the allosteric modulation of phosphofructokinase at physiological concentration of enzyme; a "slow motion" approach based on the use of a very low Mg2+/ATP ratio to conveniently lower Vmax, and the addition of polyethylene glycol as a "crowding" agent to favor aggregation of diluted enzyme. At 0.6 mg/ml muscle phosphofructokinase exhibited a drastic decrease in the ATP inhibition and the concomitant increase in the apparent affinity for fructose-6-P, as compared to a 100-fold diluted enzyme. Similar results were obtained with diluted enzyme in the presence of 10% polyethylene glycol (Mr = 6000). Results with these two approaches in vitro were essentially similar to those previously observed in situ (Aragón, J. J., Felíu, F. E., Frenkel, R., and Sols, A. (1980) Proc. Natl. Acad. Sci. U. S. A. 77, 6324-6328), indicating that the enzyme is strongly dependent on homologous interactions at physiological concentrations. With polyethylene glycol it was observed that within the physiological range of concentration of substrates and the other positive effectors, fructose-2,6-P2 still activates the liver phosphofructokinase although it no longer significantly affects the muscle isozyme. In the presence of polyethylene glycol, muscle phosphofructokinase can approach its maximal rate even in the presence of physiologically high concentrations of ATP. Three minor activities of muscle phosphofructokinase have been studied at high enzyme concentration: the hydrolysis of MgATP (ATPase) and fructose-1,6-P2 (FBPase), produced in the absence of the other substrate, and the reverse reaction from MgADP and fructose-1,6-P2. The kinetic study of these activities has allowed a new insight into the mechanisms involved in the modulation of phosphofructokinase activity. The binding of (Mg)ATP at its regulatory site reduces the ability of the enzyme to cleave the bond of the terminal phosphate of MgATP at the substrate site. The positive effectors (Pi, cAMP, NH+4, fructose-1,6-P2, and fructose-2,6-P2) decrease the inhibitory effect of MgATP. Citrate and fructose-2,6-P2 both act as mechanistically "secondary" effectors in the sense that citrate does not inhibit and fructose-2,6-P2 does not activate the FBPase activity, requiring both the presence of ATP to affect the enzyme activity. In conclusion it appears that the regulatory behavior of mammalian phosphofructokinases is utterly dependent on the fact of their high concentrations in vivo.

Adenosine Triphosphatases↗
PubMed1985

Nuclear magnetic resonance studies of fructose 2,6-bisphosphate and adenosine 5'-monophosphate interaction with bovine liver fructose-1,6-biphosphatase.

1H and 31P nuclear magnetic resonance was used to investigate the interaction of AMP and fructose 2,6-bisphosphate (Fru-2,6-P2) with bovine liver fructose-1,6-bisphosphatase. Mn2+ bound to fructose-1,6-bisphosphatase was used as a paramagnetic probe to map the active and AMP allosteric sites of fructose-1,6-bisphosphatase. Distances between enzyme-bound Mn2+ and the phosphorus atoms at C-6 of fructose-6-P and alpha-methyl-D-fructofuranoside 1,6-bisphosphate were identical, and the enzyme-Mn to phosphorus distance determined for the C-6 phosphorus atom of Fru-2,6-P2 was very similar to these values. Likewise, the enzyme-Mn to phosphorus distances for Pi, the C-1 phosphorus atom of alpha-methyl-D-fructofuranoside 1,6-bisphosphate, and the C-2 phosphorus atom of Fru-2,6-P2 agreed within 0.5 A. The distance between enzyme-bound Mn2+ and the phosphorus atom of AMP was significantly shorter than the distances obtained for any of the aforementioned ligands, but the presence of Fru-2,6-P2 caused the enzyme-Mn to phosphorus distance for AMP to lengthen markedly. NMR line broadening of AMP protons was studied at various temperatures. The dissociation rate constant was found to be greater than 20 s-1. It was concluded that Fru-2,6-P2 strongly affects the interaction of AMP with fructose-1,6-bisphosphatase and that the sugar most likely acts at the active site of the enzyme.

Adenosine Monophosphate↗
PubMed1985

The effect of organic solvents on the activation and the activity of spinach chloroplast fructose-1,6-bisphosphatase.

A two-stage assay was used to study the effect of organic solvents on the activation of and the catalysis by chloroplast fructose-1,6-bisphosphatase. Irrespective of chemical structure, all the organic solvents tested had a dual effect on the enzyme. In the activation they stimulated and inhibited at low and high concentrations, respectively, in a process that required dithiothreitol, fructose 1,6-bisphosphate, and Ca2+. Conversely, organic solvents inhibited catalysis. The enhancement in fructose-1,6-bisphosphatase activity did not arise from a change in the molecular weight of the enzyme and correlated positively with the hydrophobic character of the organic solvent. In the presence of 2-propanol, all the activation constants for modulators (fructose 1,6-bisphosphate, a2+, thioredoxin-f) were lower than in a strictly aqueous medium. Monothiols were also functional in the activation of chloroplast fructose-1,6-bisphosphatase, although they were less effective than dithiols. Sulfhydryl compounds decreased the concentration of fructose 1,6-bisphosphate required for the activation of the enzyme, and 2-propanol lowered this requirement further. Arrhenius plots were nonlinear for the enzyme activation and linear for the hydrolytic step. The anomalous temperature dependence of the chloroplast fructose-1,6-bisphosphatase activation was indicative of a cooperative process. The data obtained in this study indicate that the concerted activation of chloroplast fructose-1,6-bisphosphatase is favored in a medium less polar than water.

1-Propanol↗