Cytosolic phosphofructokinase 1 catalyzes the reaction of fructose 6-phosphate and ATP to form fructose 1,6-bisphosphate and ADP. This reaction, irreversible under physiological conditions, is the rate limiting step of glycolysis. Phosphofructokinase 1 activity is allosterically regulated by ATP, citrate, and fructose 2,6-bisphosphate.
Phosphofructokinase 1 is active as a tetramer (although higher order multimers, not annotated here, may form in vivo). Two isoforms of phosphofructokinase 1 monomer, L and M, are widely expressed in human tissues. Different tissues can contain different homotetramers or heterotetramers: L4 in liver, M4 in muscle, and all possible heterotetramers, L4, L3M, L2M2, LM3, and M4, in red blood cells, for example (Raben et al. 1995; Vora et al. 1980, 1987; Vora 1981). A third isoform, P, is abundant in platelets, where it is found in P4, P3L, P2L2, and PL3 tetramers (Eto et al. 1994; Vora et al. 1987).