fructose16diphosphate

Fructose-1,6-diphosphate, also known as fructose bisphosphate, is an important intermediate in both glycolysis and gluconeogenesis. It is formed from the phosphorylation of fructose-6-phosphate by the enzyme phosphofructokinase-1, a key regulatory step in glycolysis. Conversely, it is broken down into fructose-6-phosphate by fructose-1,6-bisphosphatase in gluconeogenesis.

This molecule plays a crucial role in energy metabolism. In glycolysis, its formation commits glucose to be broken down for energy. The subsequent cleavage of fructose-1,6-bisphosphate by aldolase yields two three-carbon molecules, dihydroxyacetone phosphate and glyceraldehyde-3-phosphate, which continue through the glycolytic pathway. In gluconeogenesis, the reverse reaction regenerates fructose-6-phosphate, allowing for the synthesis of glucose from non-carbohydrate precursors.

The interconversion between fructose-6-phosphate and fructose-1,6-diphosphate is tightly regulated by cellular energy levels. High levels of ATP and citrate inhibit phosphofructokinase-1, slowing glycolysis, while AMP and fructose-2,6-bisphosphate activate it, promoting glucose breakdown. The enzyme fructose-1,6-bisphosphatase, involved in gluconeogenesis, is regulated in a reciprocal manner, being inhibited by AMP and fructose-2,6-bisphosphate. This coordinated regulation ensures that glycolysis and gluconeogenesis do not occur simultaneously at a high rate, preventing futile cycling.