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Phosphofructokinase-2 (PFK2) is one activity of a bifunctional enzyme (EC 2.7.1.105), the other of which is fructose 2,6-bisphosphatase (FBPase2). When serine 32 is phosphorylated, the negative charge causes the conformation of the enzyme to favor the FBPase2 activity. When not phosphorylated, PFK2's activity is favored.
[edit] Function
This bifunctional enzyme is present principally in cells that have responsibility for regulation of glucose concentrations in the bloodstream, for example, some liver cells. In response to hormonal signals - for example, the release of insulin or epinephrine - PFK2 and FBPase2 form, or hydrolyze, respectively, the compound β-D-fructose 2,6-bisphosphate (F-2,6-BP), a regulatory molecule controlling the activity of the enzyme phosphofructokinase-1 or PFK1 (in mammals). PFK1, in turn, is a key regulatory enzyme in the central metabolic pathway - glycolysis. When PFK2 activity is favored, ADP is formed from ATP in the phosphorylation of fructose-6-phosphate to F-2,6-BP. The ADP acts as a positive effector ligand PFK1, which converts fructose-6-phosphate (F-6-P) into F-1,6-BP. Thus, PFK2 increases the rate at which the principal food molecule glucose is broken down. At the same time, F-2,6-BP inhibits the opposing enzyme (FBPase1) in the reverse pathway (gluconeogenesis) so that the synthesis of glucose is not taking place in the same cell where glucose is being broken down (a futile cycle).
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