Henri-Géry Hers

Fructose 2,6‐Bisphosphate

Fructose 2,6-biphosphate present in animal tissues, higher plants and fungi, is a potent stimulator of phosphofructokinase and an inhibitor of fructose 1,6-bisphosphatase. It aslo stimulates plant PPi-fructose 6-phosphate phosphotransferase. It is formed from fructose 6-phosphate in the liver by a specific 6-phosphofructo 2-kinase and converted back to fructose 6-phosphate by a specific fructose 2,6-biphosphatase. These two enzymes are controlled by the concentration of various metabolites and also through phosphorylation by cyclic AMP-dependent protein kinase. Fructose 2,6-biphosphate is an intracellular signal which signifies that glucose is abundant; in this respect, its action is opposed to that of cyclic AMP.

Fructose 2,6-bisphosphate in relation with the resumption of metabolic activity in slices of Jerusalem artichoke tubers

When slices of Jerusalem artichoke tubers were incubated at 25°C, their concentration in fructose 2,6‐bisphosphate increased up to 250‐fold within 2 h. Fructose 2,6‐bisphosphate was also formed, although at a slower rate, in slices incubated at 0°C. Its formation could not be explained by an increase in the concentration of fructose 6‐phosphate or of ATP either by an activation of phosphofructo‐2‐kinase. Pyrophosphate—fructose‐6‐phosphate 1‐phosphotransferase was the only enzyme present in a tuber extract which was found to be sensitive to fructose 2,6‐bisphosphate. An improved procedure for the assay of fructose 2,6‐bisphosphate is also reported.

Phosphofructokinase-2 - the Enzyme That Forms Fructose 2,6-bisphosphate From Fructose 6-phosphate and Atp

Abstract An enzyme, partially purified from rat liver, catalysed the transfer of the γ-phosphoryl group of ATP to the hydroxyl present on carbon 2 of fructose 6-phosphate. This enzyme, which has been called phosphofructokinase 2, could be separated from the classical phosphofructokinase (ATP-D-fructose 6-phosphate 1-phosphotransferase) which is now called phosphofructokinase 1. The activity of phosphofructokinase 2 was stimulated by P i and AMP and inhibited P-enol -pyruvate and citrate. When measured in the high-speed supernatant obtained from isolated rat hepatocytes, the apparent activity of this enzyme was decreased several fold by treatment of the cells with glucagon.

The control of glycogen metabolism in the liver

The administration of glucose to anesthetized fed rats causes within 1 to 2 minutes the inactivation of phosphorylase; glycogen synthetase is activated only when and if the level of phosphorylase α has been taken down below a threshold value equal to approximately 10% of the total phosphorylase. The same conclusion has been reached in a study with anesthetized fed mice. These observations are adequately explained by the previously described stimulation of the phosphorylase phosphatase reaction by glucose and inhibition of synthetase phosphatase by phosphorylase α. In some experiments, insulin caused a partial inactivation of liver phosphorylase in the liver of normal rats, but more often was without effect. When effective in the diabetic animal, insulin produced the inactivation of glycogen phosphorylase and the activation of glycogen synthetase. Glucocorticoids displayed two effects: a greater activity of phosphorylase phosphatase and a decreased inhibition of synthetase phosphatase by phosphorylase α.

On the use of (3H, 14C)labelled glucose in the study of the so-called "futile cycles" in liver and muscle.

Summary High speed supernatants of liver and muscle extracts, filtered on a column of Sephadex G-25, were incubated with glucose 6-phosphate labelled with tritium in position 2, 3, 5 or 6, and uniformly with 14C. With liver filtrates, there was a preferential loss of tritium in positions 2 and 5, relative to 14C. With muscle filtrates, only the tritium in position 2 was lost. These results indicate that hydrogen exchange in position 5 of fructose 6-phosphate can occur in the liver without conversion to fructose diphosphate by phosphofructokinase, being catalyzed by transaldolase and triose phosphate isomerase. A study of the half-life of [3−3H] glucose in the blood of normal fed mice gave no evidence in favor of the operation of a futile cycle between fructose 6-phosphate and fructose diphosphate in the liver in vivo.

The Stimulation of Yeast Phosphofructokinase By Fructose 2,6-bisphosphate

1. INTRODUCTION Fructose 2,6-bisphosphate was discovered as a stimulator of rat liver PFK [l-3]. Its effect on liver and muscle PFKs is to increase the affinity of the enzyme for Fru-6-P and to relieve the inhibition by ATP with no effect on Vmax [4,5]. It is the most potent positive effector of this enzyme known at the present time. It exerts its effect at concentrations which are lOOO-fold smaller than those of Fru-1,6-P2, a classical positive effector of PFK, re- quired for the same effect 141. Fru-2,6-P2 is present in glucose-grown

Synthesis of a stimulator of phosphofructokinase, most likely fructose 2,6-bisphosphate, from phosphoric acid and fructose 6-phosphoric acid

Abstract A phosphoric ester having all the properties of the natural stimulator of phosphofructokinase recently isolated from rat liver and tentatively identified as fructose 2,6-bisphosphate [Van Schaftingen, E., Hue, L. & Hers, H.G. Biochem. J. 1980, in press] was formed by mixing 85% H 3 PO 4 with 0.2 vol of 1.8 M-fructose 6-phosphate at 0°C or 25°C. This result indicates that no compounds other than phosphate and fructose 6-phosphate enter into the structure of the stimulator. When the reaction was carried out at 25°C, fructose 1,6-bisphosphate was also formed at a slower rate than the stimulator but for a much more prolonged period.

Fructose 2,6-bisphosphate in yeast.

Abstract Fructose 2,6-bisphosphate was identified in Saccharomyces cerevisiae grown on glucose both by its property to be an acid-labile stimulator of 6-phosphofructo 1-kinase and by its ability to be quantitatively converted into fructose 6-phosphate under mild acid conditions. Fructose 2,6-bisphosphate was undetectable in cells grown on non-glucose sources. When glucose was added to the culture, fructose 2,6-bisphosphate was rapidly synthesized, reaching within 1 min concentrations able to cause a profound inhibition of fructose 1,6-bisphosphatase and a great stimulation of 6-phosphofructo 1-kinase.

Utile and futile cycles in the liver.

Summary Glucagon or glucose have been administered to normal fed rats in order to induce high rates of glycogen breakdown or synthesis. The administration of glucagon caused a 3-fold increase in the intrahepatic concentration of glucose 6-phosphate. The effect of the administration of glucose on the level of glucose 6-phosphate varied according to whether glycogen synthetase had or not been activated, being slightly elevated in the absence of activation and being lowered (40%) when an important activation had occurred. These observations are discussed with regard to the recycling of glucose and glucose 6-phosphate in the liver. It appears that the advantage of this recycling is to allow large changes in the net flux of metabolites in one or the other direction, controlled by substrate concentration only.

The effect of glucose on the conversion of muscle phosphorylase a into b or b

Abstract The stimulatory effect of glucose on the conversion of muscle phosphorylase a into b by phosphorylase phosphatase or b′ by trypsin is AMP dependent at 30°, but not at 13°. These findings explain previous disagreement concerning the effect of the hexose on the inactivation of muscle phosphorylase a by its phosphatase. This glucose effect appears to be due to the binding of the hexose to phosphorylase a .