fructose16bisfosfaat

Fructose-1,6-bisphosphate (FBP) is a phosphorylated hexose that acts as a key intermediate in cellular energy metabolism, particularly in glycolysis and gluconeogenesis. In glycolysis, FBP is formed from fructose-6-phosphate by the enzyme phosphofructokinase-1 (PFK-1) in an ATP-dependent reaction, which is a major control point of the pathway. Once produced, fructose-1,6-bisphosphate is cleaved by aldolase into two triose phosphates: glyceraldehyde-3-phosphate (GAP) and dihydroxyacetone phosphate (DHAP). DHAP is rapidly interconverted to GAP by triose phosphate isomerase, allowing downstream glycolytic steps to proceed from GAP.

FBP also serves as a regulatory node linking glycolysis and gluconeogenesis. The activity of PFK-1, which governs the forward glycolytic flux to FBP, is allosterically regulated by the cellular energy state. AMP and ADP stimulate PFK-1, while ATP and citrate inhibit it. In many tissues, fructose-2,6-bisphosphate acts as a potent allosteric activator of PFK-1, enhancing glycolysis when glucose is abundant. Conversely, in gluconeogenic conditions, fructose-1,6-bisphosphatase catalyzes the reverse reaction, converting FBP to fructose-6-phosphate and thereby bypassing PFK-1.

FBP is localized in the cytosol and represents a central branching point between two fundamental pathways of carbohydrate metabolism. Its levels and flux reflect the balance between energy production through glycolysis and glucose synthesis via gluconeogenesis.