Fructose-1,6-bisphosphatase

Definition

Fructose-1,6-bisphosphatase is a key regulatory enzyme in gluconeogenesis that catalyzes the conversion of fructose-1,6-bisphosphate to fructose-6-phosphate. This reaction is crucial for glucose synthesis from non-carbohydrate precursors, and it serves as a point of control for maintaining glucose homeostasis in the body.

5 Must Know Facts For Your Next Test

1. Fructose-1,6-bisphosphatase is inhibited by AMP and fructose-2,6-bisphosphate, signaling a low energy state and the need to shift towards glycolysis.
2. This enzyme is activated by citrate, which indicates an abundance of intermediates available for gluconeogenesis.
3. The activity of fructose-1,6-bisphosphatase is essential during fasting or low-carbohydrate intake, as it helps to maintain blood glucose levels.
4. Fructose-1,6-bisphosphatase functions in the cytosol and is distinct from its counterpart phosphofructokinase found in glycolysis.
5. Deficiencies in fructose-1,6-bisphosphatase can lead to metabolic disorders such as hypoglycemia and lactic acidosis due to impaired glucose production.

Review Questions

• How does the regulation of fructose-1,6-bisphosphatase impact gluconeogenesis?
  • The regulation of fructose-1,6-bisphosphatase plays a pivotal role in gluconeogenesis by ensuring that this pathway is activated during fasting or low-energy conditions. When energy levels are low, signals such as AMP and fructose-2,6-bisphosphate inhibit this enzyme, slowing down glucose production. Conversely, when energy levels are sufficient, citrate activates the enzyme to promote gluconeogenesis, thus helping to maintain glucose homeostasis.
• Discuss the relationship between fructose-1,6-bisphosphatase and phosphofructokinase in metabolic regulation.
  • Fructose-1,6-bisphosphatase and phosphofructokinase are key enzymes that regulate the opposing pathways of gluconeogenesis and glycolysis. Phosphofructokinase catalyzes the conversion of fructose-6-phosphate to fructose-1,6-bisphosphate in glycolysis and is activated by AMP while inhibited by ATP and citrate. In contrast, fructose-1,6-bisphosphatase works to convert fructose-1,6-bisphosphate back to fructose-6-phosphate during gluconeogenesis. Their reciprocal regulation ensures that these pathways do not operate simultaneously at high rates, maintaining metabolic efficiency.
• Evaluate the importance of fructose-1,6-bisphosphatase in overall glucose metabolism during periods of fasting or starvation.
  • Fructose-1,6-bisphosphatase is critically important for maintaining glucose metabolism during fasting or starvation. In these states, the body relies on gluconeogenesis to produce glucose from non-carbohydrate sources like amino acids and glycerol. The activity of this enzyme allows for the conversion of stored precursors into glucose which can be released into the bloodstream to provide essential energy for vital organs such as the brain. Defects or inefficiencies in this enzyme can lead to dangerously low blood sugar levels and impair the body's ability to sustain itself during prolonged periods without food.

Related terms

Gluconeogenesis: A metabolic pathway that results in the generation of glucose from non-carbohydrate substrates, primarily occurring in the liver and kidneys.

Phosphofructokinase: An important regulatory enzyme in glycolysis that converts fructose-6-phosphate to fructose-1,6-bisphosphate, playing a key role in balancing glycolysis and gluconeogenesis.

ATP:

A high-energy molecule that serves as the primary energy currency of the cell, influencing various metabolic pathways including gluconeogenesis.