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PubMed1993

6-Phosphofructo-2-kinase and control of cryoprotectant synthesis in freeze tolerant frogs.

A critical part of natural freeze tolerance is the production of low molecular weight cryoprotectants; in freeze tolerant frogs this involves a freezing-induced activation of liver glycogenolysis that leads to the accumulation of glucose as the cryoprotectant, in amounts up to 300 mM, in all organs. The present study shows that the synthesis and maintenance of high organ glucose pools is facilitated by changes in the levels of fructose-2,6-bisphosphate (F2,6P2) and an inhibition of liver 6-phosphofructo-2-kinase (PFK-2) activity that blocks the catabolism of glucose by glycolysis. Freezing exposure (24 h at -2.5 degrees C) resulted in a sharp drop in F2,6P2 levels in four organs, to 23-75% of control values, but F2,6P2 rebounded when frogs were thawed. Freezing also stimulated changes in the properties of liver PFK-2 including a decrease in maximal velocity, a basic shift in pH optimum, a 10-fold increase in Km for fructose-6-phosphate, and increased I50 values for enzyme inhibitors. I50 values for glycerol-3-phosphate and phosphoenolpyruvate were 60- and 2.4-fold higher, respectively, for liver PFK-2 from frozen frogs compared with controls. Changes in liver PFK-2 properties are consistent with a freezing-induced phosphorylation of the enzyme to produce a less active enzyme form, resulting in reduced organ F2,6P2 levels and a decrease in 6-phosphofructo-1-kinase activity.

Adaptation, Physiological↗
PubMed1993

Pyrophosphate: fructose-6-phosphate 1-phosphotransferase and biosynthetic capacity during differentiation of hypocotyls of Vigna seedlings.

The relationship between the activity of pyrophosphate:fructose-6-phosphate 1-phosphotransferase (PFP) and the capacity for biosynthesis of macromolecules was examined in segments from different parts of hypocotyls of etiolated seedlings of Vigna mungo and V. radiata. The relative ratio of the maximum activity of PFP to that of ATP-dependent phosphofructokinase (PFK) (PFP/PFK ratio) was high in young tissues and decreased with differentiation and ageing of the tissues. The highest level of fructose-2,6-bisphosphate was observed in the youngest part of hypocotyls of V. mungo. The level was markedly decreased with ageing of tissues. The levels of PPi and ATP were also higher in younger parts than in older parts of the hypocotyls, but the ratio of the level of PPi to that of ATP was almost constant in all parts of the hypocotyl. A good correlation was found between the PFP/PFK ratio and the biosynthetic capacity, as estimated from the rate of incorporation of [U-14C]sucrose into ethanol-insoluble macromolecules.

Aging↗
PubMed1983

Some comparative properties of pyruvate kinase in haematopoietic cells and erythrocytes from rainbow trout (Salmo gairdneri R).

1. Temperature acts as a pyruvate kinase regulator in haematopoietic cells and erythrocytes. 2. Fructose-1,6-biphosphate and alanine act as allosteric modulators of pyruvate kinase in haematopoietic cells, while in erythrocytes although fructose-1,6-biphosphate exerts also allosteric effect, alanine appears to be a competitive inhibitor. ATP (1.0 mM) does not exert any clear effect on pyruvate kinase of both cellular populations. 3. The level of specific activity of pyruvate kinase in haematopoietic cells is 40-fold that of PK from erythrocytes.

Adenosine Triphosphate↗
PubMed1984

Regulation of glycolysis in lizards: kinetic studies on liver pyruvate kinase and phosphofructokinase from Lacerta galloti.

Kinetic studies were carried out on pyruvate kinase and phosphofructokinase from the lizard Lacerta galloti. Pyruvate kinase is inhibited by ATP and activated by fructose 1,6-biphosphate giving an hyperbolic saturation curve for ATP without the activator which becomes sigmoidal at saturating concentrations of fructose 1,6-biphosphate, giving a moderate cooperativity with a Hill coefficient of h = 1.72. Binding of fructose 1,6-biphosphate to pyruvate kinase was studied as protection effect against thermal denaturation, this being the most suitable ligand tested to avoid the loss of activity. Phosphofructokinase is inhibited by ATP at millimolar range and activated by AMP and by fructose 2,6-biphosphate, AMP being the more efficient activator.

Adenosine Monophosphate↗
PubMed1985

Comparative kinetic studies of Mn2+-activated and fructose-1,6-P-modified Mg2+-activated pyruvate kinase from Concholepas concholepas.

Initial velocity and product inhibition studies of Mn2+-activated and FDP-modified Mg2+-activated pyruvate kinase from Concholepas concholepas, were performed. Evidence is presented to show that the Mn2+-enzyme catalyzes an ordered sequential mechanism, with ADP being the first substrate and pyruvate the last product. The results presented are consistent with a random combination of reactants with the FDP-modified Mg2+-activated enzyme and the formation of the dead-end complexes enzyme ADP-ATP and enzyme-PEP-ATP.

Animals↗
PubMed1987

Comparative kinetic behaviour and regulation by fructose-1,6-bisphosphate and ATP of pyruvate kinase from erythrocytes, reticulocytes and bone marrow cells.

1. Kinetic and regulatory properties of pyruvate kinase have been studied in haemolysates of erythrocytic populations from blood and bone marrow of rats. 2. Pyruvate kinase from normal rat erythrocytes showed sigmoidal kinetics vs phosphoenolpyruvate. In contrast, the enzyme from reticulocytes and erythroid-rich bone marrow cells behaved as hyperbolic. 3. The enzyme activities were always inhibited by ATP. Activation by fructose-1,6-bisphosphate was only observed in erythrocytes. 4. These kinetic differences suggest changes in pyruvate kinase isozymes in cells of the erythrocytic line of rats.

Adenosine Triphosphate↗
PubMed1987

Effects of 5-hydroxytryptamine, cyclic AMP, AMP, and fructose 2,6-bisphosphate on phosphofructokinase activity in Hymenolepis diminuta.

1. 5-HT (10(-4) M) had no effect on the activity of phosphofructokinase in Hymenolepis diminuta. Concentrations of ATP above 33 microM inhibited PFK activity; AMP and cyclic AMP relieved this inhibition. 2. Local levels of cyclic AMP may be indirectly modulated by NaF, guanylyl imidophosphate, or 5-HT in the presence of GTP, which stimulates adenylyl cyclase activity x2 in H. diminuta homogenates. 3. Fructose 2,6-bisphosphate (F2BP), a physiological regulator of PFK activity in rat liver, also relieved ATP-induced inhibition of PFK. F2BP was present in supernatants from the worms at about 20 mumol/g wet wt. 4. 5-HT may cause an increase in the rate of glycolysis in H. diminuta by elevating either cyclic AMP and/or AMP levels; these nucleotides can in turn increase PFK activity.

1-Methyl-3-isobutylxanthine↗
PubMed1987

Glucose 1,6-bisphosphate and fructose 2,6-bisphosphate levels in different types of rat skeletal muscle.

1. The concentration of glycogen, glucose 1,6-P2, fructose 2,6-P2 and the content of glycogen phosphorylase, phosphofructokinase, 6-phosphofructo 2-kinase and glucose 1,6-P2 phosphatase activity, have been determined in rat muscles which differ in their fiber composition: extensor digitorum longus, gastrocnemius, diaphragm and soleus. 2. Glucose 1,6-P2 concentration seems to be related to the glycolytic capacity of the muscle, while fructose 2,6-P2 concentration does not. 3. No significant relationship exists between the fiber type and the content in glucose 1,6-P2 phosphatase and 6-phosphofructo 2-kinase activities.

Animals↗
PubMed1987

Kinetic properties of pyruvate kinase from the epaxial muscle of the marine fishes Mugil lisa and Chaetoditerus faber.

Kinetic studies were carried out on the reaction catalyzed by pyruvate kinase (ATP:pyruvate phosphotransferase, E.C. 2.7.1.40) purified from white striated (epaxial) muscle of two marine fish Mugil lisa (Brazilian mullet) and Chaetoditerus faber (harvest fish). This included the establishment of kinetic parameters. Attention was given to the effect of fructose 1,6-bisphosphate (Fru-P2) on PK activity. Effects of ATP, alanine and the divalent ions, Mg2+, Mn2+, Cu2+, Be2+ and Co2+, on the fish muscle enzyme were also studied.

Adenosine Diphosphate↗
PubMed1988

The effect of fructose 1,6 diphosphate on pyruvate kinase from the liver of the flounder (Platichthys flesus L.).

1. Pyruvate kinase purified from flounder liver in two forms, i.e. PKI and PKII, is activated by fructose 1,6 diphosphate. 2. Two or more binding sites for FDP are demonstrated for PKII, the binding to which is influenced by the levels of substrates. 3. FDP reduces or abolishes the cooperative effect of PEP. 4. FDP increases the maximal activity. 5. The inhibition observed at higher levels of ADP is not abolished by FDP.

Adenosine Diphosphate↗
PubMed1988

Effects of fructose 2,6-bisphosphate and glucose 1,6-bisphosphate on phosphofructokinase from chicken erythrocytes.

1. Phosphofructokinase (EC 2.7.1.11) from chicken erythrocytes is activated by fructose 2,6-bisphosphate, glucose 1,6-bisphosphate and AMP, and it is inhibited by 2,3-bisphosphoglycerate and inositol hexaphosphate. 2. The stimulatory effects produced by the two bisphosphorylated hexoses are additive and the effects produced by fructose 2,6-bisphosphate and by AMP are synergistic. 3. The activatory effect produced by fructose 2,6-bisphosphate is counteracted by fructose 1,6-bisphosphate. 4. The inhibition produced by both 2,3-bisphosphoglycerate and inositol hexaphosphate is released by fructose 2,6-bisphosphate. 5. It is concluded that, like phosphofructokinase from mammalian tissues, the enzyme from chicken erythrocytes can be modulated by the relative concentrations of those metabolites.

Adenosine Monophosphate↗
PubMed1989

Occurrence and characterization of fructose 6-phosphate, 2-kinase and fructose 2,6-bisphosphatase in Euglena gracilis.

1. Fructose 6-phosphate, 2-kinase and fructose 2,6-bisphosphatase occurred in Euglena gracilis SM-ZK, and is located in cytosol. 2. Fructose 6-phosphate, 2-kinase and fructose 2,6-bisphosphatase were partially purified, and both enzyme activities were not separated during the partial purification. 3. The pH optimum for fructose 6-phosphate, 2-kinase activity was 7.0. The saturation curve of the enzyme activity for ATP concentration was hyperbolic, and the Km value for the substrate was 0.88 mM. On the other hand, the saturation curve of the enzyme activity for fructose 6-phosphate concentration was sigmoidal, and the K0.5 value for the substrate was 70 microM. 4. The pH optimum for fructose 2,6-bisphosphatase activity was 6.5. The saturation curve for fructose 2,6-bisphosphate concentration was sigmoidal, and the K0.5 value for the substrate was 1.29 microM. Fructose 2,6-bisphosphate showed a substrate inhibition at high concentration over 5 microM, and the enzyme activity was completely inhibited by 20 microM of fructose 2,6-bisphosphate.

Animals↗
PubMed1989

Comparison of phosphofructokinases in submandibular glands of immature and adult rats.

1. Phosphofructokinases (PFKs) in immature and adult rat submandibular glands were purified to near homogeneity, and their properties were compared. 2. PFK in immature gland was less sensitive to inhibition by ATP than adult PFK. 3. Saturation curve for fructose 6-phosphate of PFK in immature gland was less sigmoidal than that of adult PFK indicating the lower cooperativity of subunits in immature PFK. 4. Fructose 2,6-bisphosphate relieved PFK from inhibition by ATP in adult gland, but a similar effect was not clearly observed in immature gland PFK. 5. Adult PFK was a heterotetramer consisting of C-, M-, L-subunits, but in immature PFK another type of subunit, which was slightly smaller than L-subunit, existed in addition to C-, M- and L-subunits.

Adenosine Triphosphate↗
PubMed1990

Fructose 2,6-bisphosphate in liver of Sparus aurata: influence of nutritional state.

1. Fructose 2,6-bisphosphate (fru-2,6-P2) has been measured in liver and muscle of gilthead sea bream fish, Sparus aurata. 2. The fru-2,6-P2 levels in liver depend on the diet given to the fish: in fish fed a high carbohydrate diet, the fru-2,6-P2 levels are higher than any one previously reported. These changes are associated with differences in the phosphofructokinase 2 activity. 3. Fru-2,6-P2 levels has also been measured in liver of Sparus aurata after different fasting periods. In starved fish, fru-2,6-P2 did not decrease as sharply as in rat. The values found in fish starved for 20 days were similar to those reported for rats that had been starved for 24 hr.

Animals↗
PubMed1991

Kinetic characterization of phosphofructokinase isolated from rat kidney cortex.

1. Phosphofructokinase from rat kidney cortex has been purified by affinity chromatography to a final specific activity of 15 units per mg of protein, measured at 25 degrees C and pH 8. 2. This lower spec. act., compared with that of the enzyme from other sources, shows the enzyme in proximal tubules to be less active, which would account for the main gluconeogenic role of these nephron sections. 3. The binding of fructose-6-phosphate to the enzyme is co-operative. ATP increases the Hill coefficient and produces a marked allosteric inhibition on the activity. 4. Fructose-2,6-bis-phosphate is a potent activator of the enzyme from this source. It reduces the Hill coefficient of the enzyme and the inhibition constant of ATP. A marked difference between this and the liver enzyme is that the activation is not co-operative.

Adenosine Triphosphate↗
PubMed1991

The hydrolysis of phosphatidylinositol 4-phosphate in membranes of Xenopus laevis oocytes: characteristics of a phosphomonoesterase.

1. Phosphatidylinositol 4-phosphate (PtdIns4P) is degraded by isolated membranes from Xenopus laevis oocytes. 2. Incubation of [4-32P]PtdIns4P with membranes yields only radioactive inorganic phosphate, indicating the presence of a phosphomonoesterase. 3. Membranes hydrolyze Ptd[2-3H]Ins4P to produce mainly Ptd[2-3H]Ins in the lipid phase. In this incubation [3H]inositol and inositol monophosphate appear in the water phase. 4. Membrane incubations of Ptd[2-3H]Ins4P carried out in the presence of excess non-radioactive Ins(1,4)P2 allows the trapping of small amounts of [3H]Ins(1,4)P2. These results demonstrate the presence of a phospholipase C. 5. Testing several phosphorylated analogs, it is determined that fructose 1,6-bisphosphate and alpha-glycerophosphate are potent inhibitors of the oocyte PtdIns4P phosphomonoesterase.

Animals↗
PubMed1993

Kinetic parameters of human and rabbit liver D-fructose 1,6-diphosphate 1-phosphohydrolase determined at 25 and 37 degrees C.

1. Kinetic parameters of human and rabbit liver D-fructose 1,6-diphosphate 1-phosphohydrolase (EC 3.1.3.11) (FDP-ase) at 25 and 37 degrees C have been determined. 2. Km determined at 25 degrees C were 1.4 microM for human and 1.6 microM for rabbit enzyme; at 37 degrees C, corresponding values were 1.7 and 1.8 microM. 3. Both enzymes are allosterically inhibited by AMP. Respective values of I0.5 were 7.2 microM for human and 13.2 microM for rabbit at 25 degrees C, and 16.6 microM for human and 27.3 microM for rabbit at 37 degrees C. 4. Fructose 2,6-diphosphate, a potent regulator of gluconeogenesis, is more effective at 25 than at 37 degrees C. Ki determined at 25 degrees C was 0.07 microM for human and 0.035 microM for rabbit in comparison with 0.17 microM for human and 0.09 microM for rabbit at 37 degrees C. 5. Affinity of FDP-ase for magnesium is also dependent on temperature. For the human enzyme, Km at 25 degrees C was 226 microM and at 37 degrees C, 176 microM. For the rabbit enzyme, corresponding values were 256 and 240 microM. 6. Both enzymes are activated by KCl. Determined values of A0.5 were 91 mM for human, and 50 mM for rabbit enzyme at 25 degrees C, and 129 mM for human and 100 mM for rabbit enzyme at 37 degrees C.

Adenosine Monophosphate↗
PubMed1994

Purification and kinetic properties of phosphofructokinase from Rana ridibunda erythrocytes.

Phosphofructokinase (PFK) from Rana ridibunda erythrocytes was purified about 570-fold by column chromatography on Cibacron Blue Sepharose. The resulting enzyme preparation had a specific activity of 1.94 U/mg protein and a pH maximum of 7.6. The molecular weight as determined by HPLC chromatography was 330,000 Da. The S0.5 value for fructose-6-phosphate (F6P) was 5.6 mM and the Km for ATP 0.87 mM. The enzyme was sensitive to inhibition by ATP which was increased with lower F6P concentrations. At physiological levels of 2,3-diphosphoglycerate (0.35 mumol/ml RBC), 20% of PFK activity was inhibited. Significant activations under cellular conditions were exercised by AMP and, to a lesser extent, by Pi. Micromolar concentrations of fructose-2,6-bisphosphate and glucose-1,6-bisphosphate were also potent activators of the erythrocyte enzyme. Fructose-1,6-bisphosphate (10-50) microM activated the enzyme to a limited extent. With respect to these effects, it is suggested that PFK is a significant enzyme in regulating the glycolytic flux of Rana ridibunda red blood cells. The existence of a regulatory mechanism controlled by the energy status of the red cell, as well as the state of oxygenation of haemoglobin, is discussed, in which PFK occupies a central role.

2,3-Diphosphoglycerate↗