Phosphofructokinase

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Phosphofructokinase

Bacterial Phosphofructokinase: 3rd glycolysis enzyme (smaller than in Eukaryots). In yellow=sugars; in red=ATP-ADP; starred=regulatory sites (PDB code=4pfk) (more details...)

"PFK" redirects here. PFK (Poulet Frit Kentucky) is also the name for KFC in French-speaking Quebec, Canada.

Phosphofructokinase-1 (PFK-1) is the most important regulatory enzyme (EC 2.7.1.11) of glycolysis. It is an allosteric enzyme made of 4 subunits and controlled by several activators and inhibitors. PFK-1 catalyzes what is considered the first "committed" step of glycolysis, the conversion of fructose 6-phosphate and ATP to fructose 1,6-bisphosphate and ADP.

α-D-fructose 6-phosphate	Phosphofructokinase-1		α-D-fructose 1,6-bisphosphate
	ATP	ADP
	Pi	H2O
	Fructose bisphosphatase

This step is subject to extensive regulation since it is not only irreversible, but also because the original substrate is forced to proceed down the glycolytic pathway after this step. This leads to a precise control of glucose and the other monosaccharides galactose and fructose going down the glycolysis pathway. Before this enzyme's reaction, glucose-6-phosphate can potentially travel down the pentose phosphate pathway, or be converted to glucose-1-phosphate and polymerized into the storage form Glycogen.

[edit] Regulation

PFK1 is allosterically inhibited by ATP and citrate (from the citric acid cycle) and its product. It is also inhibited by low pH to prevent the accumulation of hydrogen ions in muscle. The enzyme has two sites with different affinities for ATP which is both a substrate and an inhibitor.

PFK1 is allosterically activated by a high concentration of AMP, but the most potent activator is fructose 2,6-bisphosphate, which is also produced from fructose-6-phosphate by PFK2.

PFK is inhibited by glucagon through repression of synthesis.

The precise regulation of PFK 1 prevents glycolysis and gluconeogenesis from occurring simultaneously.

[edit] Genes

There are three phosphofructokinase genes in humans:

• PFKL - liver
• PFKM - muscle
• PFKP - platelet

[edit] See also

• PFK2 (converts fructose 6-phosphate to fructose 2,6-bisphosphate)
• PFP (reversibly interconverts fructose 6-phosphate and fructose 1,6-bisphosphate using inorganic pyrophosphate (rather than ATP)
• fructose bisphosphatase (hydrolyses fructose 1,6-bisphosphate to fructose 6-phosphate)

[edit] External links

• MeSH Phosphofructokinases

v • d • e  Glycolysis Metabolic Pathway

Glucose Glucose-6-phosphate Fructose 6-phosphate Fructose 1,6-bisphosphate Dihydroxyacetone phosphate Glyceraldehyde 3-phosphate Glyceraldehyde 3-phosphate ATP ADP ATP ADP NAD+ + Pi NADH + H+ + 2 NAD+ + Pi NADH + H+ 1,3-Bisphosphoglycerate 3-Phosphoglycerate 2-Phosphoglycerate Phosphoenolpyruvate Pyruvate Acetyl-CoA ADP ATP H2O ADP ATP CoA + NAD+ NADH + H+ + CO2 2 2 2 2 2 2 ADP ATP H2O