F2,6BP is a very potent activator of phosphofructokinase (PFK-1) that is synthesized when F6P is phosphorylated by a second phosphofructokinase (PFK2). In the liver, when blood sugar is low and glucagon elevates cAMP, PFK2 is phosphorylated by protein kinase A. The phosphorylation inactivates PFK2, and another domain on this protein becomes active as fructose bisphosphatase-2, which converts F2,6BP back to F6P. Both glucagon and epinephrine cause high levels of cAMP in the liver. The result of lower levels of liver F2,6BP is a decrease in activity of phosphofructokinase and an increase in activity of fructose 1,6-bisphosphatase, so that gluconeogenesis (in essence, "glycolysis in reverse") is favored. This is consistent with the role of the liver in such situations, since the response of the liver to these hormones is to release glucose to the blood.
F26BP is a very potent activator of phosphofructokinase (PFK-1) that is synthesized when F6P is phosphorylated by a second phosphofructokinase (PFK2) In the liver when blood sugar is low and glucagon elevates cAMP PFK2 is phosphorylated by protein kinase A The phosphorylation inactivates PFK2 and another domain on this protein becomes active as fructose bisphosphatase-2 which converts F26BP back to F6P Both glucagon and epinephrine cause high levels of cAMP in the liver The result of lower levels of liver F26BP is a decrease in activity of phosphofructokinase and an increase in activity of fructose 16-bisphosphatase so that gluconeogenesis (in essence "glycolysis in reverse") is favored This is consistent with the role of the liver in such situations since the response of the liver to these hormones is to release glucose to the blood