Fructose16bisphosphatase

Fructose-1,6-bisphosphate (FBP) is a phosphorylated derivative of the six-carbon sugar fructose, with phosphate groups esterified to the 1 and 6 positions. It is a key intermediate in central carbohydrate metabolism, linking glycolysis and gluconeogenesis.

Biochemical formation and fate: In glycolysis, the enzyme phosphofructokinase-1 (PFK-1) catalyzes the ATP-dependent phosphorylation of fructose-6-phosphate to fructose-1,6-bisphosphate. Fructose-1,6-bisphosphate is subsequently cleaved by aldolase into two triose phosphates: dihydroxyacetone phosphate and glyceraldehyde-3-phosphate, which continue through glycolysis to generate energy. In gluconeogenesis, fructose-1,6-bisphosphatase removes the phosphate group at C1 to regenerate fructose-6-phosphate, allowing glucose production when cellular energy or biosynthetic needs require it.

Regulation and significance: The step forming FBP is a major control point in glycolysis, responding to cellular energy status. PFK-1 activity is allosterically regulated by ATP, AMP, citrate, and other metabolites; in many tissues, fructose-2,6-bisphosphate also modulates PFK-1. As such, FBP levels reflect metabolic flux through glycolysis and gluconeogenesis. The molecule is produced and consumed in the cytosol of cells and serves as a substrate for subsequent enzymatic reactions that generate or conserve energy.