Phosphofructokinase (PFK)

PFK (also called PFK-1) is an enzyme of glycolysis that is a critical control point regulating the pathway. It catalyzes the conversion of fructose-6-phosphate (F6P) to fructose-1,6-bisphosphate (F1,6BP) by adding a phosphate from ATP, creating ADP.

> F6P + ATP <=> F1,6BP + ADP + H+

The enzyme is regulated allosterically and the of the reaction (-14.2 kJ/mol) is sufficiently negative to make it essentially irreversible in vivo. Consequently gluconeogenesis uses the enzyme fructose-1,6-bisphosphatase to hydrolyze F1,6BP to F6P. PFK is,thus, one of the glycolysis enzymes that is not used in gluconeogenesis.

Allosteric activators of PFK include AMP and fructose-2,6-bisphosphate (F2,6BP). Inhibitors include ATP and citrate. The most potent of the allosteric regulator of glycolysis and gluconeogenesis is F2,6BP due to its ability to turn on PFK and turn off the corresponding gluconeogenesis enzyme, fructose-1,6-bisphosphatase, in very low concentrations.

Higher plants contain two different PFKs - the ATP-dependent enzyme described above and a second, unique form that uses pyrophosphate instead of ATP as the phorporylating agent. The reaction catalyzed is as follows:

> F6P + PPi <=> F1,6BP + Pi

PFK is inhibited by light in plants.

Previous step of glycolysis; Next step of glycolysis

See also: Enzymes of Glycolysis, Gluconeogenesis, Regulation of Glycolysis, Glycolysis/Gluconeogenesis Regulation Links, Regulation of Photosynthesis

INTERNET LINKS:

> 1. RasMol Structure of PFK (slow)

> 2. Glycolysis/Gluconeogenesis