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At least 163 records · Page 9Linked to original sources
PubMed1995

Fructose 2,6-bisphosphate metabolism in Ehrlich ascites tumour cells.

Cancer cell energy metabolism is characterized by a high glycolytic rate, which is maintained under aerobic conditions. In Ehrlich ascites tumour cells, the concentration of fructose 2,6-bisphosphate (Fru-2,6-P2), the powerful activator of 6-phosphofructo-1-kinase, is tenfold increased. The bifunctional enzyme 6-phosphofructo-2-kinase/fructose-2,6-bisphosphatase (PFK-2/FBPase-2), synthesizing and degrading Fru-2,6-P2, was characterized. The molecular mass is 120 kDa. The dependence of PFK-2 activity on the substrate concentrations is hyperbolic (Km for Fru-6-P = 0.09 mM; Km for ATP = 0.7 mM), while the dependence of the FBPase-2 activity on the concentrations of Fru-2,6-P2 is sigmoidal (K0.5 for Fru-2,6-P2 = 4 microM). The PFK-2/FBPase-2 activity ratio is 1. PFK-2 activity is inhibited by citrate (I0.5 = 0.17 mM) and phosphoenolpyruvate (I0.5 = 0.08 mM) but only weakly by glycerol 3-phosphate (I0.5 = 1.57 mM). In contrast to the liver enzyme, the activity of tumour PFK-2/FBPase-2 is not influenced by the action of cAMP-dependent protein kinase. The kinetic properties as well as ion-exchange chromatography pattern differ from their normal counterparts in liver and muscle. The properties are likely to contribute to the maintenance of the high glycolytic rate in these tumour cells.

Alkaline Phosphatase↗
PubMed1990

2,3-Bisphosphoglycerate, fructose, 2,6-bisphosphate and glucose 1,6-bisphosphate during maturation of reticulocytes with low 2,3-bisphosphoglycerate content.

In contrast to the species with erythrocytes of high 2,3-bisphosphoglycerate content, in the sheep the concentration of 2,3-bisphosphoglycerate decreases during maturation of reticulocytes. The decrease can be explained by the drop of the phosphofructokinase/pyruvate kinase and 2,3-bisphosphoglycerate synthase/2,3-bisphosphoglycerate phosphatase activity ratios that result from the decline of phosphofructokinase, pyruvate kinase, phosphoglycerate mutase and the bifunctional enzyme 2,3-bisphosphoglycerate synthase/phosphatase. The concentrations of fructose 2,6-bisphosphate and aldohexose 1,6-bisphosphates also decrease during sheep reticulocyte maturation in parallel to the 6-phosphofructo 2-kinase and the glucose 1,6-bisphosphate synthase activities.

2,3-Diphosphoglycerate↗
PubMed1985

Biochemical observations on a case of hepatic fructose-1,6-diphosphatase deficiency.

A case of hepatic fructose-1,6-diphosphatase deficiency is described. She presented with congenital bilateral cataracts, failure to thrive, hypoglycaemia and hyperlactacidaemia. A liver biopsy revealed normal levels of gluconeogenic enzymes except fructose-1,6-diphosphatase which was present at 30% of the level of the lower control values. The residual activity had a normal affinity for fructose-1,6-diphosphate, a decreased sensitivity for inhibition by fructose-2,6-diphosphate and an increased resistance toward conversion to the AMP-insensitive form of the enzyme. As a result of this mutation, the residual FDPase will always be maintained in the AMP-inhibited form.

Adenosine Monophosphate↗
PubMed1994

The involvement of fructose 2,6-bisphosphate in substrate cycle control in the nonoxidative stage of the pentose phosphate pathway. A phosphorus magnetic resonance spectroscopy study.

The role of fructose 2,6-bisphosphate in the interconversion of sedoheptulose 7-phosphate and sedoheptulose 1,7-bisphosphate in rat liver cytosol fractions was studied by means of phosphorus magnetic resonance spectroscopy. When the activity of 6-phosphofructo-1-kinase was inhibited by a high concentration of ATP, the addition of fructose 2,6-bisphosphate led to a marked decrease in sedoheptulose 7-phosphate levels, accompanied by an increased concentration of ADP. Fructose 2,6-bisphosphate essentially inhibited both the decrease in sedoheptulose 1,7-bisphosphate concentration and the accumulation of Pi in the incubation mixture. The data provided evidence that fructose 2,6-bisphosphate can regulate the substrate cycle: sedoheptulose 7-phosphate<-->sedoheptulose 1,7-bisphosphate in the liver, and thus control the flux through the nonoxidative stage of the pentose phosphate pathway.

Animals↗
PubMed1988

Fructose-1,6-diphosphate reduces acute ECG changes due to doxorubicin in isolated rat heart.

Doxorubicin (DXR) (0.17 x 10(-4) M) induces an acute cardiotoxicity in isolated rat heart; there is a progressive widening of the S alpha T segment, with a decrease in force derivatives and in the coronary flow. Concurrent perfusion with fructose-1,6-diphosphate (FDP) (10(-5)-10(-4) M) dose-dependently reduces the S alpha T enlargement but fails to affect the reduction in force derivatives and coronary flow. The target of cardiac protection by FDP might be the ionic mechanisms underlying the action potential configuration.

Animals↗
PubMed1983

Synergistic effect of AMP and fructose 2,6-bisphosphate on the protection of fructose 1,6-bisphosphatase against inactivation by trypsin.

The rate of inactivation of chicken liver fructose 1,6-bisphosphatase by trypsin is reduced if the digestive reaction is conducted in the presence of AMP or fructose 2,6-bisphosphate. The effects of these 2 compounds are synergistic. Although fructose 1,6-bisphosphate does not protect the enzyme against tryptic inactivation, it can enhance the effect of AMP. Selective modification of the AMP allosteric site of fructose 1,6-bisphosphatase with pyridoxal-P and NaBH4 renders the enzyme more resistant to tryptic inactivation, but the modified enzyme is no longer responsive to the protective effect of AMP.

Adenosine Monophosphate↗
PubMed1985

Is it possible to maintain a normal glutathione level in lenses in vitro?

In most types of experimentally induced cataracts, glutathione (GSH) content decreases considerably before the onset of opacity. GSH may provide a protective function for protein SH groups by scavenging oxidative products that may impair lens metabolism. To avoid impairment of lens metabolism by decreased levels of GSH it may be possible in vitro: (1) to stimulate GSH synthesis by enrichment of the incubation medium with the amino acids necessary for GSH synthesis or (2) to enrich the incubation medium with the tripeptide itself so that it can be taken up by the lens. Both approaches were investigated with bovine lenses. Lenses were incubated in pairs in a salt solution without carbohydrates, so as to deplete lens of GSH. Following starvation, one lens of each pair was incubated for recovery in TCM 199 enriched with MgSO4 and the three amino acids of GSH; the other lens was put into a freshly prepared salt solution. After 6 h, lenses from the recovery solution contained more GSH than the other lenses. Addition of fructose-1,6-diphosphate to the medium enhanced this effect. When, after starvation, lenses were incubated in the presence of different amounts of GSH, GSH lens content rose, with the highest in those lenses incubated in a medium with a final molarity of 4 X 10(-3) M GSH. Therefore, incubation of lenses depleted of GSH in medium with either the amino acids of GSH or GSH itself appear to facilitate recovery of GSH content.

Animals↗
PubMed1981

Comparative inactivation and inhibition of the anomerase and isomerase activities of phosphoglucose isomerase.

Several metabolic compounds have been found to be competitive inhibitors of the anomerase activity of phosphoglucose isomerase (EC 5.3.1.9).Ki values for erythrose 4-phosphate, 6-phosphogluconate, and fructose 1,6-bisphosphate for the anomerase reaction are 0.32 muM, 21 muM, and 84 muM respectively at 0 degree and pH 8.2. A significant difference between the fructose 1,6-bisphosphate inhibition constants for both activities was found (Ki(isomerase) = 800 muM and Ki(anomerase) = 140 muM). Also the Km values for both activities were found to be significantly different (Km(isomerase) = 140 muM and Km(anomerase) = 3.6 muM). Attempts to independently alter the anomerase to isomerase activity ratio through protein modification yielded mixed results. While several modifying reagents destroyed the catalytic activities at identical rates, inactivation by iodoacetamide or pyridoxal 5' phosphate sensitized photo-oxidation displayed differential initial effects on the two activities with the anomerase activity being the less affected. These data support the theory that an imidazole residue is catalytically important for isomerization, but less so for anomerization.

Animals↗
PubMed1988

Active glycolysis and glycogenolysis in early stages of primary cultured hepatocytes. Role of AMP and fructose 2,6-bisphosphate.

This study examines the factors involved in the rapid glycolysis and glycogenolysis that occur during the first stages of hepatocyte culture: a) Shortly after seeding glycolysis, estimated as lactate released to culture medium, increased 10 times in comparison to that reported in vivo. By 8 to 9 h of culture, hepatocytes were nearly glycogen-depleted even in the presence of insulin. b) 6-Phosphofructo-2-kinase remained 100% active during this period. The proportion of the initial active phosphorylase (87%) decreased to 57% by 7 h of culture. c) Fructose 2,6-bisphosphate content was initially similar to that found in liver of fed animals, decreased after seeding and increased thereafter up to four times the initial concentration. In spite of changes in the concentration of this activator, the glycolytic rate remained high and constant. d) ADP and AMP increased sharply after cell plating, reaching values 1.7 and 3.5 times higher. The rise in AMP levels may be involved in the activation of glycolysis and glycogenolysis, because this metabolite is known to act as an allosteric activator of phosphofructokinase and glycogen phosphorylase. This metabolic situation resembles that of cells under hypoxia.

Adenosine Diphosphate↗
PubMed1991

Beneficial effects of fructose-1,6-diphosphate infusion on liver regeneration after ischemic liver injury.

The effect of fructose-1,6-diphosphate (FDP) on cellular viability after partial hepatectomy in partial ischemic liver was investigated in rats. The administration of FDP did not increase blood flow in the hepatic tissue; however, it significantly suppressed the elevation of serum liver functions for 24 hours after partial hepatectomy. Levels of DNA synthesis, protein synthesis, and labeling index were significantly higher in the groups administered divided doses of FDP before and after partial hepatic ischemia than in the control group (P less than 0.01). Thus, these findings indicate that FDP has cytoprotective and hepatotrophic effects on liver with ischemic injury and that divided dose administration of FDP is more effective than bolus doses in decreasing damage following ischemic and reperfusion injury.

Animals↗
PubMed2005

The effect of fructose-1, 6-diphosphate and HTK solution on protecting primary cardiac muscle cells of rat with cold preservation.

In this study we tried to investigate the effect of fructose-1,6-diphosphate and HTK solution on protecting primary cardiac muscle cells of rat with cold preservation. The primary cardiac muscle cells of rat were cultured in vitro with four preservation solutions respectively: 0.9% sodium chloride solution (group A), FDP (group B), HTK solution (group C) and a mixture of FDP and HTK solution (group D). The cells were preserved for 6, 8 and 10 h at 0-4 degrees C. The values of AST and LDH-L and the Na+-K+ ATPase activity in cardiac muscle cells were detected, and the survival rate of cardiac muscle cells was detected with trypan blue staining. The values of AST and LDH-L in group C and group D were remarkable lower those in group A and group B (P<0.001), while the Na+-K+ ATPase activity and the survival rate of cells in group C and group D were much higher than those in group A and group B (P<0.001). The values of AST and LDH-L after 6 hours in group D decreased much more than those in group C (P<0.01), while the Na+-K4 ATPase activity and the survival rate of cells in group D improved more than those in group C (P<0. 01). Both of the HTK solution and the mixture of HTK and FDP solution have an evident effect on protecting the primary cardiac muscle cells of rat in vitro with cold preservation, Compared with the HTK solution, the mixture solution has a better short-term protective effect.

Animals↗
PubMed1989

Immobilization of pig muscle aldolase on a silica-based support.

Pig muscle aldolase was covalently attached to a silica-based support possessing aldehyde functional groups. The activity of the immobilized enzyme was 37 U/g solid, and the specific activity calculated on a bound protein basis was 1.9 U/mg protein. The optimum pH for the catalytic activity was pH 7.5. The apparent optimum temperature was found to be 45 degrees C. The Km app value of the immobilized aldolase with D-fructose 1,6-diphosphate as substrate was 1.25 X 10(-4) M. The conformational stability was improved by the immobilization. The immobilized aldolase was used for the continuous splitting of D-fructose 1,6-diphosphate.

Animals↗
PubMed1997

Fusion and metabolism of plant cells as affected by microgravity.

Plant cell protoplasts derived from leaf tissue of two different tobacco species (Nicotiana tabacum., N. rustica L.) were exposed to short-term (sounding rocket experiments) and long-term (spacelab) microgravity environments in order to study both (electro) cell fusion and cell metabolism during early and later stages of tissue regeneration. The period of exposure to microgravity varied from 10 min (sounding rocket) to 10 d (space shuttle). The process of electro fusion of protoplasts was improved under conditions of microgravity: the time needed to establish close membrane contact between protoplasts (alignment time) was reduced (5 as compared to 15 s under 1 g) and numbers of fusion products between protoplasts of different specific density were increased by a factor of about 10. In addition, viability of fusion products, as shown by the ability to form callus, increased from about 60% to more than 90%. Regenerated fusion products obtained from both sounding-rocket and spacelab experiments showed a wide range of intermediate properties between the two parental plants. This was verified by isozyme analysis and random amplified polymorphic DNA-polymerase chain reaction (RAPD-PCR). In order to address potential metabolic responses, more general markers such as the overall energy state (ATP/ADP ratio), the redox charge of the diphosphopyridine nucleotide system (NADH/NAD ratio), and the pool size of fructose-2,6-bisphosphate (Fru 2,6 bisp), a regulator of the balance between glycolysis and gluconeogenesis, were determined. Responses of these parameters were different with regard to short-term and long-term exposure. Shortly after transition to reduced gravitation (sounding rocket) ratios of ATP/ADP exhibited strong fluctuation while the pool size of NAD decreased (indicating an increased NADH/NAD ratio) and that of Fru 2,6 bisp increased. As similar changes can be observed under stress conditions, this response is probably indicative of a metabolic stress compensation. Samples taken for up to 7 d of exposure to microgravity showed the opposite effect. Here, the ratios of ATP/ADP and of NADH/NAD, and the pool size of Fru 2,6 bisp were decreased. We take this an an indication of metabolic relaxation, i.e. decreased metabolic turnover. As rates of protoplast regeneration and cell division were obviously similar to 1-g controls, we conclude that under conditions of microgravity regenerating tobacco mesophyll protoplasts need less metabolic energy for the same effort.

Adenine Nucleotides↗
PubMed2006

The effects of fructose-1,6-bisphosphate and dexamethasone on acute inflammation and T-cell proliferation.

OBJECTIVE AND DESIGN: Chronic glucocorticoid treatment is associated with pharmacological resistance. We investigated the auxiliary effects of fructose-1,6-bisphosphate (FBP) on dexamethasone (DEX)-related modulation of inflammation and T-cell proliferation. METHODS: Acute inflammation (pleurisy) was induced by injection of carrageenan into the pleural cavity of rats that were treated in vivo with DEX s. c. and FBP i. p. Peripheral blood mononuclear cells were isolated and T-cell sensitivity to FBP and DEX was evaluated in vitro. RESULTS: FBP and DEX reduced the exudate volume, protein concentration and neutrophils in the pleural cavity. However no synergistic effects were observed when these compounds were tested simultaneously. In contrast, both compounds dose-dependently and synergistically suppressed T-cell proliferation. CONCLUSION: These data suggest that FBP may be beneficial as auxiliary drug for the treatment of patients with acquired glucocorticoid resistance.

Animals↗
PubMed2001

Tungstate is an effective antidiabetic agent in streptozotocin-induced diabetic rats: a long-term study.

AIMS/HYPOTHESIS: Recent studies have shown the anti diabetic effects of oral sodium tungstate treatment in several animal models of diabetes based on short-term experiments. In this study, we examined the effectiveness of long-term tungstate treatment of streptozotocin-induced-diabetic rats. METHODS: Tungstate was administered to the drinking water of rats for eight months. RESULTS: The treatment resulted in a reduction in serum glucose concentrations in diabetic rats, but no change in glycaemia was detected in healthy rats. Alterations in the hepatic glucose metabolism due to diabetes were almost completely counteracted by tungstate treatment. The partial recovery of glucokinase activity, not found in diabetic animals, normalised glycogen and glucose 6-phosphate concentrations. Tungstate treatment also restored pyruvate kinase activity and fructose 2,6-bisphosphate concentrations. In healthy rats, tungstate treatment did not modify the majority of the hepatic parameters studied. Moreover, tungstate treatment prevented diabetes-induced morphological changes in the kidney and ocular lens and also reduced mortality. Furthermore, no hypoglycaemic episodes or undesirable side effects were observed in treated diabetic or healthy rats. In addition, there is no evidence of intolerance developing after prolonged use. CONCLUSION/INTERPRETATION: Tungstate could play a helpful part in the long-term treatment of diabetes.

Aging↗