The mechanism by which ethanol decreases the concentration of fructose 2,6-bisphosphate in the liver.

The intragastric administration of ethanol to fed rats caused in their liver, within about 1 h, a 20-fold decrease in the concentration of fructose 2,6-bisphosphate, an activation of fructose 2,6-bisphosphatase, an inactivation of phosphofructo-2-kinase but no change in the concentration of cyclic AMP. Incubation of isolated hepatocytes in the presence of ethanol caused a rapid increase in the concentration of sn-glycerol 3-phosphate and a slower and continuous decrease in the concentration of fructose 2,6-bisphosphate with no change in that of hexose 6-phosphates. There was also a relatively slow activation of fructose 2,6-bisphosphatase and inactivation of phosphofructo-2-kinase.

Effects of glucose and glucagon on the fructose 2,6-bisphosphate content of pancreatic islets and purified pancreatic B-cells. A comparison with isolated hepatocytes.

Glucose caused a sustained and dose-related increase in the fructose 2,6-bisphosphate content of isolated pancreatic islets, as well as of purified pancreatic B-cells. With isolated B-cells, the glucose saturation curve was sigmoidal and superimposable on that obtained with hepatocytes isolated from unfed rats. However, the response to glucose was notably faster in purified B-cells than in isolated hepatocytes.

The ability of adenosine to decrease the concentration of fructose 2,6-bisphosphate in isolated hepatocytes. A cyclic AMP-mediated effect.

The presence of adenosine (25-250 microM) or of 2-chloroadenosine (2.5-100 microM) in the incubation medium caused a marked decrease in the concentration of fructose 2,6-bisphosphate in isolated hepatocytes. This effect was accompanied by an increase in the concentration of cyclic AMP, an activation of phosphorylase and of fructose 2,6-bisphosphatase, and an inactivation of pyruvate kinase and of 6-phosphofructo-2-kinase.

Fructose 2,6-bisphosphate and germination of fungal spores.

Induction of germination of Phycomyces blakesleeanus spores by a heat shock and subsequent incubation at 25 degrees C in a glucose- or 6-deoxyglucose-containing culture medium resulted in an intense (20-40 times the initial value) rise in the concentration of fructose 2,6-bisphosphate and hexose 6-phosphates. The increase in the concentration of fructose 2,6-bisphosphate but not that of hexose 6-phosphates was restricted to a 25-min period during which the spores acquired an irreversible capacity to germinate. Incubation of the spores in water for any period of time during this critical period resulted in a parallel decrease in their ability to form hexose phosphates and to germinate.

Hormonal control of fructose 2,6-bisphosphate concentration in isolated rat hepatocytes.

The ability of glucagon and of adrenaline to affect the concentration of fructose 2,6-bisphosphate in isolated hepatocytes was re-investigated because of important discrepancies existing in the literature. We were unable to detect a significant difference in the sensitivity of the hepatocytes with regard to the effect of glucagon to initiate the interconversion of phosphorylase, pyruvate kinase, 6-phosphofructo-2-kinase and fructose 2,6-bisphosphatase, and also to cause the disappearance of fructose 2,6-bisphosphate. In contrast, we have observed differences in the time-course of these various changes, since the interconversions of phosphorylase and of pyruvate kinase were at least twice as fast as those of 6-phosphofructo-2-kinase and of fructose 2,6-bisphosphatase.

On the mechanism of inhibition of neutral liver fructose 1,6-bisphosphatase by fructose 2,6-bisphosphate.

The inhibitory effect of fructose 2,6-biphosphate on fructose 1,6-bisphosphatase was reinvestigated in order to solve the apparent contradiction between competition with the substrate and the synergism with AMP, a strictly noncompetitive inhibitor. The effect of fructose 2,6-bisphosphate was compared to that of other ligands of the enzyme, which, like the substrate and methyl (alpha + beta)fructofuranoside 1,6-bisphosphate bind to the active site or which, like AMP, bind to an allosteric site. An increase in temperature or pH, or the presence of sulfosalicylate, lithium or higher concentrations of magnesium as well as partial proteolysis by subtilisin increased [I]0.

The role of fructose 2,6-bisphosphate in the long-term control of phosphofructokinase in rat liver.

The phosphofructokinase stabilizing factor, believed to be a peptide of molecular weight 3,800 (Dunaway G.A. and Segal H.

A kinetic study of pyrophosphate: fructose-6-phosphate phosphotransferase from potato tubers. Application to a microassay of fructose 2,6-bisphosphate.

Pyrophosphate : fructose-6-phosphate phosphotransferase (PPi-PFK) has been purified 150-fold from potato tubers and the kinetic properties of the purified enzyme have been investigated both in the forward and the reverse direction. Saturation curves for fructose 6-phosphate and also for fructose 1,6-bisphosphate were sigmoidal whereas those for PPi and Pi were hyperbolic. In the presence of fructose 2,6-bisphosphate, the affinity for fructose 6-phosphate and for fructose 1,6-bisphosphate were greatly increased and the kinetics became Michaëlian.

Fructose-2,6-bisphosphatase from rat liver.

An enzyme that catalyzes the stoichiometric conversion of fructose 2,6-bisphosphate into fructose 6-phosphate and inorganic phosphate has been purified from rat liver. This fructose 2,6-bisphosphatase copurified with phosphofructokinase 2 (ATP: D-fructose 6-phosphate 2-phosphotransferase) in the several separation procedures used. The enzyme was active in the absence of Mg2+ and was stimulated by triphosphonucleotides in the presence of Mg2+ and also by glycerol 3-phosphate, glycerol 2-phosphate and dihydroxyacetone phosphate.

Control of liver 6-phosphofructokinase by fructose 2,6-bisphosphate and other effectors.

Rat liver 6-phosphofructokinase (ATP-D-fructose-6-phosphate 1-phosphotransferase, EC 2.7.1.

Inhibition of fructose-1,6-bisphosphatase by fructose 2,6-biphosphate.

Fructose 2,6-bisphosphate, a known powerful stimulator of phosphofructokinase [Van Schaftingen, E., Hue, L. & Hers, H.

Stimulation of glycolysis and accumulation of a stimulator of phosphofructokinase in hepatocytes incubated with vasopressin.

Vasopressin stimulates glycolysis in hepatocytes prepared from fed rats, or from starved rats when incubated with glucose. It causes the stimulation of phosphofructokinase activity and the accumulation of a stimulator of phosphofructokinase, which is probably fructose 2,6-bisphosphate, the recently discovered stimulatory of phosphofructokinase.