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PubMed1987

Binding of zinc(II) to beta-D-fructose 2,6-bisphosphate.

The formation of a complex between Zn(II) and beta-D-fructose 2,6-bisphosphate was shown because the latter compound: activated bis(5'-guanosyl)tetraphosphatase (EC 3.6.1.17) and dinucleoside triphosphatase (EC 3.6.1.29) only to the extent that they could be inhibited by Zn(II); increased the consumption of Zn(II) necessary to titrate to an end point a solution of the metallochromic indicator eriochrome black T; coeluted with Zn(II) in a gel filtration column capable of resolving them if unbound. Neither of those effects was shown by D-fructose 1,6-bisphosphate under the same conditions.

Acid Anhydride Hydrolases↗
PubMed1987

Fluoride effects on 31P NMR spectra of macrophages.

31P High resolution nuclear magnetic resonance studies have been carried out on the P388D1 tumoral cell line and the BCG elicited alveolar rabbit macrophages both in sedimented cells and in perfused agarose-embedded cells. When the cells were sufficiently oxygenated, the phosphorylated sugars and ATP concentrations attained high levels. The intensity of the peak representing phosphorylated sugars varied inversely with ATP level when macrophagic cells were treated by NaF. The identities of the phosphorylated sugars were revealed by 1H and 31P NMR studies of the P 388D1 cells perchloric extracts.

Adenosine Triphosphate↗
PubMed1988

Comparative effects of interleukin 1 and a phorbol ester on rheumatoid synovial cell fructose 2,6-bisphosphate content and prostaglandin E production.

The addition of either recombinant human interleukin 1 (IL1 alpha) or 12-O-tetradecanoyl phorbol-13-acetate (TPA) to cultured rheumatoid synovial cells (RSC) caused dose-related increases in PGE production and cellular fructose 2,6-bisphosphate (Fru-2,6-P2). IL1 consistently produced the greater increases in both parameters. A close association between increases in PGE production and Fru-2,6-P2 was demonstrated for both IL1- and TPA-stimulated cells. The combined addition of IL1 with TPA resulted in an additive increase in both parameters. When IL1 was added together with human recombinant interferon-gamma (IFN-gamma), the resulting Fru-2,6-P2 level was synergistically increased, whilst the combination of IFN-gamma and TPA produced only an additive increase. Thus despite their very similar effects on RSC in culture, the data suggests that IL1 and TPA do not act via an identical intracellular mechanism.

Cells, Cultured↗
PubMed1988

Inactivation of fructose-1,6-bisphosphatase by o-phthalaldehyde.

Rabbit liver fructose-1,6-bisphosphatase, a tetramer of identical subunits was rapidly and irreversibly inactivated by o-phthalaldehyde at 25 degrees C (pH 7.3). The second-order rate constant for the inactivation was 30 M-1s-1. Fructose-1,6-bisphosphatase was completely protected from inactivation by the substrate--fructose-1,6-diphosphate but not by the allosteric effector--adenosine monophosphate. The absorption spectrum (lambda max 337 nm) and, fluorescence excitation (lambda max 360 nm) and fluorescence emission spectra (lambda max 405 nm) were consistent with the formation of an isoindole derivative in the subunit between a cysteine and a lysine residue about 3A apart. About 4 isoindole groups per mol of the bisphosphatase were formed following complete loss of the phosphatase activity. This suggests that the amino acid residues of the biphosphatase participating in reaction with o-phthalaldehyde more likely reside at or near the active site instead of allosteric site. The molar transition energy of fructose-1,6-bisphosphatase--o-phthalaldehyde adduct was estimated 121 kJ/mol and compares favorably with 127 kJ/mol for the synthetic isoindole, 1-[(beta-hydroxyethyl)thio]-2-(beta-hydroxyethyl) isoindole in hexane. It is, thus, concluded that the cysteine and lysine residues participating in isoindole formation in reaction between fructose-1,6-bisphosphatase and o-phthalaldehyde are located in a hydrophobic environment.

Adenosine Monophosphate↗
PubMed1989

Endotoxin increases the liver fructose 2,6-bisphosphate concentration in fasted rats.

Following endotoxin administration to fasted rats, the liver fructose 2,6-bisphosphate level is significantly increased within 1 hr, is elevated 2.3-fold by 3 hrs, and remains elevated 2 to 3-fold for at least 24 hrs. This increase in the potent allosteric activator of phosphofructokinase occurs when there is no change in the liver Glc 6-P, glycogen or cAMP concentrations, or in the activities of phosphoenolpyruvate carboxykinase or pyruvate kinase. The increase in fructose 2,6-bisphosphate concentration accounts for the increased phosphofructokinase activity previously observed in hepatocytes isolated 18 hours following endotoxin administration to rats (1). By stimulating the phosphofructokinase/Fru 1,6-bisphosphate cycle in the direction of glycolysis, fructose 2,6-bisphosphate is likely the factor responsible for decreased gluconeogenesis in endotoxemia.

Animals↗
PubMed1990

Regulation of phosphofructokinase at physiological concentration of enzyme studied by stopped-flow measurements.

Stopped-flow measurements have been carried out to study some basic allosteric properties of muscle and yeast phosphofructokinase at physiological concentration of enzyme. An important increase in the affinity for fructose-6-P accompanied by an intense decrease in the ATP inhibition was observed with the muscle enzyme, which also became insensitive to fructose-2,6-P2 under these conditions. Yeast phosphofructokinase exhibited a significant diminution in the inhibition by ATP, although with no apparent change in the affinity for fructose-6-P. These results provide strong support in favor of the dependence of the allosteric regulation of phosphofructokinase on its concentration in vivo.

Adenosine Triphosphate↗
PubMed1990

2',5' A synthetase: allosteric activation by fructose 1,6-bisphosphate.

Fructose 1,6-bisphosphate (fru-1,6-P2), but not other glycolytic intermediates, activates highly purified 2',5' A synthetases from rabbit reticulocyte lysates and from 2',5'-ADP-agarose purified extracts of interferon-treated HeLa cells without the addition of dsRNA. The 2',5' A was structurally and biologically identical to authentic 2',5' A. Micrococcal nuclease inhibited the activation of 2',5' A synthetase by poly(I)-poly(C), but did not affect activation by fru-1,6-P2. Addition of fru-1,6-P2 aldolase prevented the activation of 2',5' A synthetase by fru-1,6-P2.

2',5'-Oligoadenylate Synthetase↗
PubMed1991

Kinetic studies of human polymorphonuclear leukocyte phosphofructokinase.

Phosphofructokinase from human polymorphonuclear leukocytes has low cooperativity and high affinity for its substrate, F-6-P. It is resistant to ATP inhibition at pH 8; however, at pH 7.1 it becomes sensitive to the effect of this compound. It is activated by F-1, 6-P2; it is not very sensitive to citrate inhibition and F-2, 6-P2 has no effect on its activity. With these kinetic characteristics we assume that perhaps the predominant L-type subunit is accompanied by an F-type component.

Citrates↗
PubMed1991

Low glucose-1, 6-bisphosphate and high fructose-2, 6-bisphosphate concentrations in muscles of patients with glycogenosis types VII and V.

The level of glucose-1, 6-bisphosphate, a potent allosteric activator of phosphofructokinase, was markedly decreased in muscles of patients with glycogenosis type VII (muscle phosphofructokinase deficiency) and type V (muscle phosphorylase deficiency). Glucose-1-phosphate kinase activity in muscle was virtually absent in a patient with glycogenosis type VII, whereas it was normal in a patient with type V glycogenosis. Glucose-1-phosphate level was increased in type VII glycogenosis, whereas it was decreased in type V glycogenosis. Another activator of phosphofructokinase, fructose-2, 6-bisphosphate was increased in muscles of patients with both types of glycogenosis although it was much higher in type VII than in type V. This finding may be partly related to the difference of fructose-6-phosphate concentrations. The results suggest that phosphofructokinase would contribute to the major glucose-1-phosphate kinase activity in normal human muscle and would also form a kind of self-activating system.

Fructosediphosphates↗
PubMed1992

Fructose-1,6-diphosphate inhibits platelet activation.

Fructose-1,6-diphosphate (FDP) is a physiological product which exhibits pharmacological properties. This study shows that FDP (1-3 mM) inhibits platelet aggregation induced by the agonists thrombin, vasopressin, platelet activating factor, ADP, adrenaline, arachidonate and the stable thromboxane analogue U 44069. Thrombin-promoted ATP secretion and cytosolic Ca2+ rise are also drastically inhibited by FDP, which decreases, although to a lesser extent, the protein kinase C-dependent phosphorylation of the 47 kDa protein. The inhibition on thrombin-induced aggregation is shared, albeit less efficiently, by glucose-1,6-diphosphate and fructose-2,6-diphosphate but not by other phosphorylated monosaccharides (fructose-1:2 cyclic,6-diphosphate, glucose-1- and glucose-6-phosphate, fructose-1- and fructose-6-phosphate, mannose-6-phosphate and 5-phosphoryl ribose-1-pyrophosphate). FDP does not affect platelet activation induced by the protein kinase C activators dioctanoylglycerol or phorbol 12-myristate 13-acetate. No increase of cAMP concentration is observed in FDP-treated platelets. Altogether, these results indicate that FDP inhibits platelet activation at a level preceding phospholipase C. The data are consistent with a general inhibitory action of FDP on signal transmission.

Adenosine Triphosphate↗
PubMed1992

Inhibition of 6-phosphofructo-2-kinase activity by mercaptopurines.

The activity of 6-phosphofructo-2-kinase (PFK-2), the enzyme that catalyses the synthesis of fructose 2,6-bisphosphate (Fru-2,6-P2), was inhibited by mercaptopurines in vitro. Inhibition was observed with the purified enzyme from rat liver and bovine heart, and in extracts from rat lymphocytes and hepatoma cells, chick embryo fibroblasts, and human HeLa and lymphoblastoid cells. Half-maximal effect was obtained with 0.1-0.2 mM mercaptopurine and maximal inhibition ranged between 50 and 90% depending on the enzyme preparation. The inhibition resulted from a decrease in Vmax with no change in Km for ATP. The inhibition was relieved by treatment of the enzyme with thiol reducing agents, suggesting that it involves the formation of a mixed disulfide between mercaptopurine and thiol group(s) essential for enzyme activity. Incubation of intact lymphocytes or lymphoblastoid cells with 2- or 6-mercaptopurine resulted in a decrease in Fru-2,6-P2 content and lactate release. A decrease in Fru-2,6-P2 content but no change in lactate release was observed in HeLa cells and fibroblasts treated with 6-mercaptopurine but not with 2-mercaptopurine. Treatment of HeLa cells with 6-mercaptopurine resulted in a decreased PFK-2 activity which could be restored by treatment of the cell extract with dithiothreitol. In isolated rat hepatocytes and perfused rat hearts mercaptopurines had little or no effect on the Fru-2,6-P2 content and lactate release. These results suggest that the effect of 6-mercaptopurine of arresting growth in lymphoid cells might involve the inhibition of glycolysis in addition to the known inhibition of de novo purine nucleotide synthesis.

Animals↗
PubMed1980

Sequential alterations of cerebral carbohydrate metabolism associated with gamma-hydroxybutyrate.

The cerebral metabolic effects of intravenous administration of 1000 mg/kg gamma-hydroxybutyrate (GHB) were studied by sequential measurement of the cerebral contents of selected glycolytic-citric acid cycle intermediates and energy phosphates in lightly anesthetized rats. The initial change in the glycolytic pathway occurred by 2.5 min, with increases of tissue glucose-6-phosphate and decreases of fructose-1,6- diphosphate which indicated an inhibition of phosphofructokinase. This pattern was transient and was replaced at 5--15 min by increasing tissue glucose and decreasing glucose-6-phosphate which indicated an inhibition of hexokinase. The initial inhibition of phosphofructokinase was associated with functional depression, an isoelectric EEG and an increase of the tissue phosphocreatine which suggested that the observed metabolic pattern was an adaptation to the reduced energy needs of neuronal depression. Within 2.5 min of GHB injection tissue alpha-ketoglutarate and aspartate showed significant increases which suggested a shift in the aspartate aminotransferase reaction. Preliminary calculations indicated that the probable cause of this shift was an increase in oxaloacetate content due to GHB oxidation. The cytoplasmic NADH/NAD+ ratio remained unchanged throughout the entire exposure to GHB (2.5--180 min) and thus gave no support for the hypothesis that GHB interfers with glycolysis via the restriction of free cytoplasmic NAD+ required for the glyceraldehyde phosphate dehydrogenase step.

Amino Acids↗
PubMed1990

Fructose-1,6-bisphosphate reduces ATP loss from hypoxic astrocytes.

Hypoxia caused injury and metabolic dysfunction of astrocytes, as indicated by a time-dependent loss of lactate dehydrogenase (LDH) activity and ATP content. The combination of 3.5 mM fructose-1,6-bisphosphate (FBP) and 7.5 mM glucose (GLC) reduced the decrease of ATP and prevented the loss of LDH. These data indicate that the combination of GLC + FBP protects astrocytes from hypoxia. The results also suggest that the maintainance of ATP concentration is the mechanism by which FBP prevents hypoxic injury.

Adenosine Triphosphate↗
PubMed1992

Effect of starvation on glycogen and glucose metabolism in different areas of the rat brain.

We have studied the changes in concentration of glycogen, glucose and the bisphosphorylated sugars, glucose 1,6-P2 and fructose 2,6-P2, in several rat brain regions during 72 h of starvation. The animals were killed by focused microwave irradiation. The activities of glycogen metabolizing enzymes in the different areas were measured. A large decrease in glycogen and glucose concentration was observed in all areas. The concentrations of bisphosphorylated sugars changed, suggesting that an increase in glycolysis could take place at the beginning of starvation, with blood glucose as a major energy source. Differences in metabolite concentration before starvation disappeared after 72 h. The activities of glycogen synthase, glycogen phosphorylase and glycogen phosphorylase kinase were similar in all areas, and they did not change during starvation.

Animals↗