The 6-phosphofructo-2-kinase activity of cytosolic PFKFB (6-phosphofructo-2-kinase/fructose-2,6-biphosphatase) homodimer catalyzes the reaction of fructose 6-phosphate and ATP to form fructose 2,6-bisphosphate and ADP (Pilkis et al. 1988). Fructose 2,6-bisphosphate is not itself on the pathway of glycolysis. Rather, it acts as a positive allosteric effector of phosphofructokinase 1, greatly increasing the rate of synthesis of fructose 1,6-bisphosphate and hence the overall rate of glycolysis. The conversion of PFKFB between its dephosphorylated form, which catalyzes the synthesis of fructose 2,6-bisphosphate as described here, and its phosphorylated form, which catalyzes the hydrolysis of fructose 2,6-bisphosphate to fructose 6-phosphate and orthophosphate plays a central role in the short-term regulation of glycolysis (Pilkis et al. 1995).
Four isoforms of PFKFB protein encoded by four different genes exhibit tissue-specific expression patterns. PFKFB1 is expressed in the liver (Algaier and Uyeda 1988), PFKFB2 is expressed in the heart (Hirata et al. 1998), PFKFB3 is ubiquitously expressed (Manes and el-Maghrabi 2005), and PFKFB4, originally described as a testis-specific gene product (Manzano et al. 1999), may also be expressed in several kinds of tumors.