The control of glycolysis and gluconeogenesis by protein phosphorylation.

Fructose 2,6-bisphosphate has been discovered as a potent stimulator of liver phosphofructokinase. It is also an inhibitor of fructose 1,6-biphosphatase and a stimulator of PPi: fructose 6-phosphate phosphotransferase from higher plants. It is formed from fructose 6-phosphate and ATP by a 6-phosphofructo 2-kinase and hydrolysed by a fructose 2,6-bisphosphatase. These two enzymes have very similar physicochemical properties and could not be separated from each other. They are substrates for cyclic-AMP-dependent protein kinase, which inactivates the first enzyme and activates the second.