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At least 145 records · Page 8Linked to original sources
PubMed1985

Influence of fructose 2,6-bisphosphate on the phosphofructokinase/fructose 1,6-bisphosphatase cycle.

In a reconstituted enzyme system multiple stationary states and oscillatory motions of the substrate cycle catalyzed by phosphofructokinase and fructose 1,6-bisphosphatase are significantly influenced by fructose 2,6-bisphosphate. Depending on the initial conditions, fructose 2,6-bisphosphate was found either to generate or to extinguish oscillatory motions between glycolytic and gluconeogenic states. In general, stable glycolytic modes are favored because of the efficient activation of phosphofructokinase by this effector. The complex effect of fructose 2,6-bisphosphate on the rate of substrate cycling correlates with its synergistic cooperation with AMP in the activation of phosphofructokinase and inhibition of fructose 1,6-bisphosphatase.

Fructose-Bisphosphatase↗
PubMed1985

Quasi-stationary concentrations of fructose-2,6-bisphosphate in the phosphofructokinase-2/fructose-2,6-bisphosphatase cycle.

The cooperation of phosphofructokinase-2 and fructose-2,6-bisphosphatase is investigated. Experimentally derived rate laws of the kinase and bisphosphatase activities introduced into the respective differential equations permitted to describe the time evolution of fructose-2,6-bisphosphate to quasi-stationary levels. The two enzyme activities were found to exert strong temperature dependence. The quasi-stationary levels of fructose-2,6-bisphosphate, however, are independent on temperature.

Adenosine Triphosphate↗
PubMed1986

Effects of diabetes on fructose 2, 6-P2, glucose 1, 6-P2 and 6-phosphofructo 2-kinase in rat liver.

The levels of fructose 2,6-P2 and 6-phosphofructo 2-kinase have been found to be decreased in the liver of both ketotic and non-ketotic diabetic rats, a good correlation between fall of hepatic fructose 2,6-P2, ketonemia and glycemia being observed. The "total" 6-phosphofructo 2-kinase activity and the "active" (non-phosphorylated) from of the enzyme were decreased to a different extent, resulting in a fall of the "active"/"total" activity ratio. Hepatic levels of glucose 1,6-P2 were lowered only in ketotic diabetes. Insulin treatment normalized all the values studied. Insulin administration to control rats decreased the hepatic levels of fructose 2,6-P2 and did not affect glucose 1,6-P2 levels. It also decreased the "active" form of 6-phosphofructo 2-kinase, without significantly altering the "total" activity.

3-Hydroxybutyric Acid↗
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↗
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↗
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

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↗
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↗
PubMed1975

The assay of pyruvate kinase activity in gastric mucosa.

Pyruvate kinase activity in gastric mucosal supernatant preparations shows large responses to exogenous effectors. At pH 7.5, fructose 1,6-diphosphate can cause large stimulations in activity. Alanine inhibits the reaction but this effect is partially reversed by fructose 1,6-diphosphate. In the absence of these compounds, 4.0-5.0 mM phosphoenolpyruvate (PEP) is required to generate maximal activity in the assay system used. Electrophoresis reveals an isoenzyme pattern containing only one form of pyruvate kinase, an M isoenzyme, in both fundic and antral mucosa. The pyruvate kinase of gastric mucosa thus resembles the M-type enzymes of leucocytes and liver. Measurements of activity at both 1.0 mM PEP and 4.0--5.0 mM PEP, with and without additions of fructose 1,6-diphosphate, are recommended for the reliable estimation of pyruvate kinase activity in this tissue.

Animals↗
PubMed1975

Enzymatic pattern of glucose metabolic pathways in pyruvate kinase-deficient erythrocytes.

It has been shown that in some cases of congenital non-spherocytic haemolytic anaemia (CNSHA) with pyruvate kinase deficiency, the primary defect may be related to diminished magnesium-stimulated ATPase activity, followed by elevation of the erythrocyte ATP level. ATP as the end product of glycolysis inhibits by negative feedback control the activities of key glycolytic enzymes involved in energy production, i.e. pyruvate kinase (PK) and phosphofructokinase (PFK). Erythrocyte-deficient PK, however, is insensitive to the stimulating effect of fructose 1,6-diphosphate (FDP), which is normally a positive effector of PK. Both competing effectors, i.e. ATP and FDP, seem to show specific interaction. PK, inactive in the presence of high concentrations of ATP, seems to lose its sensitivity to FDP. This effect persists until ATP molecules are present in excess. In vitro incubation of deficient PK with ATPase resulted in increased PK activity as well as in recovery of its sensitivity to the stimulating effect of FDP. The same effects were obtained in vivo by administering magnesium levulinate intravenously to CNSHA patients with PK deficiency. This may indicate that magnesium ions stimulate deficient ATPase activity and lead to diminution of ATP as a negative effector for other regulatory enzymes.

Adenosine Triphosphate↗
PubMed1976

Phosphate compounds in the erythrocytes of newborns with ABO systems haemolytic disease.

The following phosphate compounds of the erythrocyte acid-soluble fraction were subjected to chromatographic separation: ADP, ATP, adenylo-diphosphoglycerate, 2,3-diphosphoglycerate, hexose monophosphate, hexose diphosphate. In each of the fractions total phosphorus, and in fraction II inorganic phosphorus, were estimated. The material was derived from ten newborns with haemolytic disease as a result of ABO incompatability and from ten full-term healthy newborns, just after birth. The concentration of the compounds assayed, except for 2,3-DPG (the values in both groups were similar) was higher in the erythrocytes from affected newborns, but lower than that found in the material derived from the newborns with Rh incompatibility. It is suggested that the metabolism of erythrocytes of the newborns with haemolytic ABO disease may be somewhat different from that in Rh incompatibility cases because in the former the haemolysis is weaker, the anaemia is less pronounced and the tissue hypoxia is of a smaller degree.

ABO Blood-Group System↗
PubMed1976

Biphasic reaction kinetics in an anomalous isozyme of erythrocyte pyruvate kinase.

A mutant erythrocyte isozyme of pyruvate kinase (PK) (ATP: pyruvate phosphotransferase, EC 2.7.1.40) has been found in associatin with chronic hemolytic anemia in two siblings who were doubly heterozygous for the isozyme and for quantitative PK deficiency of the usual form. The isozyme was characterized by approximately normal maximum reaction velocities but had markedly decreased affinity for the substrate, phosphoenolpyruvate (PEP), with 5-fold to 10-fold increases in half-saturation constants and decreased interaction between substrate binding sites. Two distinctly separable kinetic patterns for PEP were observed with multiple specimens. Concentrations of fructose 1,6-diphosphate (FDP) required for half-maximal activation were two orders of magnitude greater than controls, and optimal pH was lowered to 6.5. stability at 4 degrees C was markedly decreased, but the lost enzyme could be reactivated by fdp for periods even longer than normal controls.

Adenosine Diphosphate↗
PubMed1976

Defective erythrocyte pyruvate kinase.

A defective pyruvate kinase (EC 2.7.1.40) is described. The abnormal PK is characterized by a shift in the R in equilibrium T equilibrium to the T-state. The Ko.5 for the substrate phosphoenol pyruvate is about 6 times higher than for the normal enzyme, while the KM value for the positive effector Fru-1, 6-P2 is increased. In agreement with a shift to the T-state is the increased affinity of the abnormal enzyme for the negative effectors ATP and alanine. The results are discussed in relation to other abnormal pyruvate kinases.

Adenosine Triphosphate↗