fructose16biphosphatase

Fructose-1,6-bisphosphatase (FBPase) is a crucial enzyme involved in gluconeogenesis, the metabolic pathway that produces glucose from non-carbohydrate precursors. It catalyzes the irreversible hydrolysis of fructose-1,6-bisphosphate to fructose-6-phosphate and inorganic phosphate. This reaction is a key regulatory step in gluconeogenesis, ensuring that the cell does not simultaneously run both glycolysis and gluconeogenesis, which would be a futile cycle.

There are several isoforms of FBPase in mammals, including FBPase-1 (found primarily in the liver and kidney, the main sites of gluconeogenesis), FBPase-2 (involved in fructose metabolism), and FBPase-3. FBPase-1 is allosterically activated by citrate and inhibited by fructose-2,6-bisphosphate and AMP. These regulatory mechanisms ensure that glucose is synthesized only when blood glucose levels are low.

In plants, FBPase is also a key enzyme in the Calvin cycle, where it catalyzes the final step of regenerating ribulose-1,5-bisphosphate. This reaction is also irreversible and highly regulated. The activity of plant FBPase is controlled by light and thioredoxin, linking photosynthetic carbon fixation to the availability of light energy. Defects in FBPase activity can lead to metabolic disorders, as disruptions in glucose homeostasis can have severe consequences for cellular function and overall organismal health.