PPiPFK

PPi-dependent phosphofructokinase (PPi-PFK) is an enzyme that catalyzes the reversible phosphorylation of fructose-6-phosphate using inorganic pyrophosphate (PPi) as the phosphate donor to form fructose-1,6-bisphosphate and inorganic phosphate. It is distinct from the ATP-dependent phosphofructokinase (PFK-1), which uses ATP as the phosphate donor. PPi-PFK has been identified in various bacteria and archaea and has also been reported in some plant tissues, where it participates in a PPi-dependent variant of glycolysis that can conserve cellular ATP under certain conditions.

Biochemical features of PPi-PFK include its dependence on divalent metal ions, typically Mg2+, for catalytic activity. The reaction is generally reversible, with the direction influenced by substrate and energy-state conditions. Structural studies in some organisms indicate a dimeric organization with active sites formed at subunit interfaces, and conserved residues that coordinate PPi binding and phosphotransfer.

Regulation and physiological role of PPi-PFK vary across organisms. In systems that also possess ATP-dependent PFK, PPi-PFK provides an alternative route for fructose-6-phosphate phosphorylation, enabling glycolytic flux under conditions where ATP is limited or where PPi is relatively abundant. This can contribute to energy conservation in anaerobic or PPi-producing environments.

Nomenclature for this enzyme includes PPi-dependent phosphofructokinase, PPi-PFK, pyrophosphate-dependent phosphofructokinase, and EC 2.7.1.90. Its existence highlights metabolic flexibility in microorganisms and plants, illustrating how glycolysis can be adapted to different cellular energy currencies.