Phosphofructokinase 1

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

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.

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.

Genes
There are three phosphofructokinase genes in humans:
 * - liver
 * - muscle
 * - platelet