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Fructose 2,6-bisphosphate

 

 
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Fructose 2,6-bisphosphate
 
 
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Fructose 2,6-bisphosphate (or fructose 2,6-diphosphate), abbreviated Fru-2,6-P2, is a metabolite which allosterically affects the activity of the enzymes phosphofructokinase 1 (PFK-1) and fructose 1,6-bisphosphatase (FBPase-1) to regulate glycolysis
Glycolysis

Glycolysis is the metabolic pathway that converts glucose, C6H12O6, into pyruvate, C3H5O3-....
 and gluconeogenesis
Gluconeogenesis

Gluconeogenesis is a metabolic pathway that results in the generation of glucose from non-carbohydrate carbon substrates such as lactic acid, glycerol, and glucogenic amino acids....
.

Fru-2,6-P2 is synthesized and broken down by the bifunctional enzyme, phosphofructokinase 2/fructose-2,6-bisphosphatase (PFK-2/FBPase-2).






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Fructose 2,6-bisphosphate (or fructose 2,6-diphosphate), abbreviated Fru-2,6-P2, is a metabolite which allosterically affects the activity of the enzymes phosphofructokinase 1 (PFK-1) and fructose 1,6-bisphosphatase (FBPase-1) to regulate glycolysis
Glycolysis

Glycolysis is the metabolic pathway that converts glucose, C6H12O6, into pyruvate, C3H5O3-....
 and gluconeogenesis
Gluconeogenesis

Gluconeogenesis is a metabolic pathway that results in the generation of glucose from non-carbohydrate carbon substrates such as lactic acid, glycerol, and glucogenic amino acids....
.

Fru-2,6-P2 is synthesized and broken down by the bifunctional enzyme, phosphofructokinase 2/fructose-2,6-bisphosphatase (PFK-2/FBPase-2).

The synthesis of Fru-2,6-P2 is performed through the phosphorylation of fructose 6-phosphate
Fructose 6-phosphate

Fructose 6-phosphate is fructose sugar phosphorylated on carbon 6 . The ?-D-form of this compound is very common in cell . The vast majority of glucose and fructose entering a cell will become converted to this at some point....
 using ATP by the PFK-2 portion of the enzyme. The breakdown of Fru-2,6-P2 is catalyzed by dephosphorylation by FBPase-2 to produce Fructose 6-phosphate and Pi.

Reaction scheme of breakdown of fructose 2,6-bisphosphate to fructose 6-phosphate.

Effects on glucose metabolism

Fru-2,6-P2 strongly activates glucose
Glucose

Glucose , a monosaccharide also known as grape sugar, blood sugar, or corn sugar, is a very important carbohydrate in biology....
 breakdown in glycolysis through allosteric modulation of phosphofructokinase 1. Elevated expression of Fru-2,6-P2 levels in the liver allosterically activates phosphofructokinase 1 by increasing the enzyme’s affinity for fructose 6-phosphate, while decreasing its affinity for inhibitory ATP and citrate
Citrate

A citrate can refer either to the conjugate base of citric acid, , or to the esters of citric acid. An example of the former, a salt is trisodium citrate; an ester is triethyl citrate....
. At physiological concentration, PFK-1 is almost completely inactive, but interaction with Fru-2,6-P2 activates the enzyme to stimulate glycolysis and enhance breakdown of glucose.

Fru-2,6-P2 stimulates glucose breakdown further through reduction of gluconeogensis through allosteric inhibition of fructose 1,6-bisphosphatase. Increased levels of Fru-2,6-P2 show dramatically reduced rates of fructose 1,6-bisphosphatase (FBPase-1) activity, with greater degrees of inhibition occurring at lower concentrations of Fru-2,6-P2. This inhibition also appears synergistic with AMP, another allosteric inhibitor of FBPase-1. This coordination between Fru-2,6-P2 and AMP allows similar inhibition of FBPase-1 with dramatically reduced levels of inhibitory AMP. Inhibition by Fru-2,6-P2, however, appears reduced at elevated pH and temperature levels.

Production regulation

The concentration of Fru-2,6-P2 in cells is controlled through regulation of the synthesis and breakdown by PFK-2/FBPase-2. The primary regulators of this are the hormones insulin
Insulin

Insulin is a hormone with extensive effects on both metabolism and several other body systems . Insulin causes most of the body's cells to take up glucose from the blood , storing it as glycogen in the liver and muscle, and stops use of fat as an energy source....
 and glucagon
Glucagon

Glucagon is an important hormone involved in carbohydrate metabolism. Produced by the pancreas, it is released when the glucose level in the blood is low , causing the liver to convert stored glycogen into glucose and release it into the bloodstream....
 which affect the enzyme through phosphorlyation/dephosphorylation reactions. Release of the hormone glucagon triggers production of cyclic adenosine monophosphate
Cyclic adenosine monophosphate

Cyclic adenosine monophosphate is a second messenger that is important in many biological processes. cAMP is derived from adenosine triphosphate and used for intracellular signal transduction in many different organisms....
 (cAMP) which activates a cAMP-dependent protein kinase. This kinase phosphorylates the PFK-2/FBPase-2 enzyme at an NH2-terminal Ser residue with ATP to activate the FBPase-2 activity and inhibit the PFK-2 activity of the enzyme, thus reducing levels of Fru-2,6-P2 in the cell. With decreasing amounts of Fru-2,6-P2, glycolysis becomes inhibited while gluconeogenesis is activated. Insulin triggers the opposite response, as a phosphoprotein phosphatase
Phosphoprotein phosphatase

Phosphoprotein phosphatase is an enzyme which dephosphorylates certain phosphorylated proteins....
 dephosphorylates the enzyme to activate the PFK-2 and inhibit the FBPase-2 activities. With additional Fru-2,6-P2 present, activation of PFK-1 occurs to stimulate glycolysis while inhibiting gluconeogenesis.

Regulation of sucrose production

Fru-2,6-P2 plays an important role in the regulation of triose phosphates, the end products of the Calvin Cycle
Calvin cycle

The Calvin cycle is a series of biochemistry reactions that take place in the Stroma of chloroplasts in photosynthesis organisms. It was discovered by Melvin Calvin, James Bassham and Andrew Benson at the University of California, Berkeley ....
. In the Calvin Cycle, 5/6th of triose phosphates are recycled to make ribulose 1,5-bisphosphate. The remaining 1/6th of triose phosphate can be converted into sucrose
Sucrose

Sucrose is a disaccharide of glucose and fructose, with the molecular formula C12H22O11. Its systematic name is a-D-glucopyranosyl- -?-D-fructofuranoside ....
 or stored as starch. Fru-2,6-P2 inhibits production of fructose 6-phosphate, a necessary element for sucrose synthesis. When the rate of photosynthesis
Photosynthesis

File:Seawifs global biosphere.jpgPhotosynthesis is a metabolic pathway that converts carbon dioxide into organic compounds, especially sugars, using the energy from sunlight....
 in the light reactions is high, triose phosphates are constantly produced and the production of Fru-2,6-P2 is inhibited, thus producing sucrose. Fru-2,6-P2 production is activated when plants are in the dark and photosynthesis and triose phosphates are not produced.

See also

  • Fructose 2,6-bisphosphatase
    Fructose 2,6-bisphosphatase

    Fructose-2,6-bisphosphatase is an enzyme that catalyzes the following reaction:fructose-2,6-bisphosphate + H2O ---> fructose 6-phosphate + phosphate ion...
  • Fructose 1,6-bisphosphate
    Fructose 1,6-bisphosphate

    Fructose 1,6-phosphate is fructose sugar phosphorylated on carbons 1 and 6 . The ?-D-form of this compound is very common in cell ....