Fructose-2,6-bisphosphatase from rat liver

Area of Science:

• Biochemistry
• Enzymology

Background:

• Fructose 2,6-bisphosphate is a key regulator of glycolysis and gluconeogenesis.
• Understanding the enzymes involved in its metabolism is crucial for comprehending metabolic regulation.

Purpose of the Study:

• To purify and characterize a fructose 2,6-bisphosphatase from rat liver.
• To investigate the regulatory mechanisms of this enzyme's activity.

Main Methods:

• Enzyme purification from rat liver.
• Enzyme activity assays under various conditions (e.g., presence of different substrates, cofactors, and inhibitors).
• Investigation of enzyme activation by cyclic-AMP-dependent protein kinase and cyclic AMP.
• Measurement of enzyme activity in crude liver preparations and hepatocyte extracts after glucagon treatment.

Main Results:

• A fructose 2,6-bisphosphatase was purified and found to copurify with phosphofructokinase 2.
• The enzyme's activity was modulated by triphosphonucleotides, glycerol phosphates, and dihydroxyacetone phosphate.
• Fructose 6-phosphate inhibited the enzyme, an effect partially reversed by glycerol phosphate and dihydroxyacetone phosphate.
• Enzyme activity was significantly increased by cyclic-AMP-dependent protein kinase and cyclic AMP, and by glucagon treatment in hepatocytes.
• Activation involved an increase in Vmax and enhanced sensitivity to ATP and glycerol phosphate.

Conclusions:

• Rat liver possesses a fructose 2,6-bisphosphatase whose activity is tightly regulated.
• Hormonal regulation, particularly via glucagon and cyclic AMP, plays a significant role in modulating enzyme activity.
• The enzyme's complex regulation suggests its importance in controlling carbohydrate metabolism in the liver.