What is the significance of fructose 1,6-bisphosphate in regulating pyruvate kinase activity?

Fructose 1,6-bisphosphate acts as a critical positive allosteric effector for certain isoforms of pyruvate kinase (PK). In its absence, PK exists mainly as a monomer; however, when fructose 1,6-bisphosphate is present, it promotes tetramerization of PK, enhancing its catalytic activity and facilitating glycolysis.