title: Fructose 2,6-bisphosphate and glycolytic oscillations in skeletal muscle extracts.
abstract: Oscillatory behavior of glycolysis in cell-free extracts of rat skeletal muscle involves bursts of phosphofructokinase activity due to autocatalytic activation by fructose-1,6-P2. Fructose-2,6-P2 is an even more potent activator of phosphofructokinase and is competitive with fructose-1,6-P2 in binding and kinetic studies. The possible role and effects of fructose-2,6-P2 on the oscillating system were therefore examined. When muscle extracts were provided with 1 mM ATP and 10 mM glucose, fructose-2,6-P2 slowly accumulated to 50 nM in 1 h. The nearly monotonic rise, in contrast to the 50-fold oscillations in fructose-1,6-P2, indicated no involvement of fructose-2,6-P2 in the oscillatory process. Addition of 0.5 microM fructose-2,6-P2 blocked the oscillations, and there was negligible appearance of glycolytic intermediates from fructose-1,6-P2 to phosphoenolpyruvate, although similar amounts of lactate accumulated. In the presence of 0.2 microM fructose-2,6-P2, there were small, transient accumulations of fructose-1,6-P2, suggesting aborted activations of phosphofructokinase. Oscillations were not blocked by 0.1 microM fructose-2,6-P2. The average [ATP]/[ADP] ratio in the presence of 0.2 or 0.5 microM fructose-2,6-P2 was half the value in its absence, demonstrating the advantage of the oscillatory behavior in maintaining a high energy state. In the presence of higher, near physiological levels of ATP and citrate, inhibitors which reduce the affinity of phosphofructokinase for fructose-2,6-P2, glycolytic oscillations were not blocked by 1 microM fructose-2,6-P2, its approximate concentration in vivo.
mesh_terms: D000818:Animals; D002951:Citrates / Q000378:metabolism; D019343:Citric Acid; D004099:Dihydroxyacetone Phosphate / Q000378:metabolism; D005635:Fructosediphosphates / Q000378:metabolism*; D019298:Glucose-6-Phosphate; D005958:Glucosephosphates / Q000378:metabolism; D005988:Glyceric Acids / Q000378:metabolism; D006019:Glycolysis; D006598:Hexosediphosphates / Q000378:metabolism*; D007700:Kinetics; D009132:Muscles / Q000378:metabolism*; D010728:Phosphoenolpyruvate / Q000378:metabolism; D010732:Phosphofructokinase-1 / Q000378:metabolism; D051381:Rats
chemical_list: D002951:Citrates; D005635:Fructosediphosphates; D005958:Glucosephosphates; D005988:Glyceric Acids; D006598:Hexosediphosphates; D019343:Citric Acid; D019298:Glucose-6-Phosphate; D004099:Dihydroxyacetone Phosphate; D010728:Phosphoenolpyruvate; C027652:fructose 2,6-diphosphate; C005156:3-phosphoglycerate; D010732:Phosphofructokinase-1; C029063:fructose-1,6-diphosphate