Fructose 2,6-bisphosphate (Fructose 2,6-bisphosphate, abbreviated as Fru-2,6-P2) is the enzyme phosphofructokinase 1 (PFK-1) and fructose-1. , 6-Bisphosphatase (FBPase-1) is a metabolite that affects allosteric activity and regulates glycolysis and gluconeogenesis. Fru-2,6-P2 is synthesized and degraded by the dual functional enzyme phosphofructokinase 2 / fructose-2,6-bisphosphatase (PFK-2 / FBPase-2).
The synthesis of Fru-2,6-P2 is carried out through the phosphorylation of fructose-6-phosphate with ATP by the PFK-2 portion of the enzyme. Degradation of Fru-2,6-P2 is catalyzed by dephosphorylation by FBPase-2 to produce fructose-6-phosphate and Pi.
Effects on glucose metabolism
Fru-2,6-P2 strongly activates glucose degradation in glycolysis through the allosteric regulation of phosphofructokinase 1. Although PFK1 is almost completely inactive at physiological concentrations, its interaction with Fru-2,6-P2 activates enzymes, stimulates glycolysis and enhances glucose degradation.
Regulation of generation
The concentration of Fru-2,6-P2 in cells is regulated by the regulation of synthesis and degradation by PFK-2 / FB Pase-2. The main regulators of this are the hormones insulin, glucagon and adrenaline, which affect enzymes through phosphorylation / dephosphorylation reactions. Glucagon release initiates the production of cyclic adenosine monophosphate (cAMP), which activates cAMP-dependent protein kinases. This enzyme phosphorylates the serine residue at the NH2-terminal of PFK-2 / FBPase-2, activates FBPase-2 activity, and inhibits PFK-2 activity. This reduces the intracellular amount of Fru-2,6-P2. When the amount of Fru-2,6-P2 decreases, glycolysis is inhibited and gluconeogenesis is activated. Insulin initiates the opposite response. As a phosphoprotein phosphatase, insulin dephosphorylates the enzyme, resulting in activation of PFK-2 and inhibition of FBPase-2. The presence of additional Fru-2,6-P2 causes activation of PFK-1 and stimulates glycolysis, while inhibiting gluconeogenesis.
Regulation of sucrose production
Fru-2,6-P2 plays an important role in the regulation of triosephosphate, the final product of the Calvin cycle. In the Calvin cycle, five-sixths of triosephosphate is recycled to make ribulose-1,5-bisphosphate. The remaining one-sixth is converted to sucrose or stored as starch. Fru-2,6-P2 inhibits the production of fructose-6-phosphate, which is essential for sucrose synthesis. When the rate of photosynthesis in the photoreaction is high, triose phosphates are always produced, and the production of Fru-2,6-P2 is inhibited, resulting in the production of sucrose. The production of Fru-2,6-P2 is activated when the plant is in dark conditions.