key term - Phosphoenolpyruvate carboxykinase

Definition

Phosphoenolpyruvate carboxykinase (PEPCK) is an enzyme that catalyzes the conversion of oxaloacetate to phosphoenolpyruvate, a key step in gluconeogenesis. This process is crucial for maintaining blood glucose levels during fasting or low-carbohydrate intake and connects gluconeogenesis to other metabolic pathways, particularly the citric acid cycle.

5 Must Know Facts For Your Next Test

1. PEPCK exists in two isoforms: one located in the cytosol and the other in the mitochondria, allowing for regulation in different cellular environments.
2. The activity of PEPCK is regulated by various factors, including hormone levels (like glucagon and insulin) and substrate availability, which ensures that gluconeogenesis occurs when energy is needed.
3. PEPCK plays a vital role not only in gluconeogenesis but also in the conversion of amino acids and lactate into glucose, emphasizing its importance in metabolic flexibility.
4. In mammals, PEPCK is primarily expressed in the liver and kidney, tissues crucial for maintaining glucose homeostasis.
5. Deficiencies in PEPCK can lead to hypoglycemia and other metabolic disorders due to impaired gluconeogenesis.

Review Questions

• How does phosphoenolpyruvate carboxykinase contribute to gluconeogenesis, and what role does it play in maintaining blood glucose levels?
  • Phosphoenolpyruvate carboxykinase (PEPCK) plays a pivotal role in gluconeogenesis by catalyzing the conversion of oxaloacetate to phosphoenolpyruvate. This step is essential for synthesizing glucose from non-carbohydrate sources when carbohydrates are scarce. By facilitating gluconeogenesis, PEPCK helps maintain blood glucose levels during fasting or low-carb intake, ensuring that vital organs receive sufficient energy.
• Discuss the regulatory mechanisms that control phosphoenolpyruvate carboxykinase activity and their physiological significance.
  • The activity of phosphoenolpyruvate carboxykinase is tightly regulated by hormones like glucagon and insulin, which respond to blood glucose levels. Glucagon stimulates PEPCK expression to promote gluconeogenesis when blood sugar is low, while insulin has the opposite effect. This hormonal regulation ensures that glucose production aligns with the body's energy needs, highlighting its physiological significance in maintaining metabolic homeostasis.
• Evaluate the potential impact of impaired phosphoenolpyruvate carboxykinase function on overall metabolism and energy homeostasis.
  • Impaired function of phosphoenolpyruvate carboxykinase can have profound effects on metabolism and energy homeostasis. A deficiency may lead to inadequate gluconeogenesis, resulting in hypoglycemia, particularly during fasting or strenuous exercise. This can cause weakness, confusion, and other symptoms related to low blood sugar levels. Furthermore, as PEPCK is involved in converting various substrates into glucose, its dysfunction can disrupt overall metabolic flexibility and nutrient utilization.

Related terms

Gluconeogenesis: The metabolic pathway that generates glucose from non-carbohydrate substrates, essential for maintaining energy supply during periods of fasting.

Oxaloacetate: A four-carbon intermediate in the citric acid cycle and gluconeogenesis, formed from the metabolism of pyruvate and other substrates.

Citric Acid Cycle: A central metabolic pathway that generates energy through the oxidation of acetyl-CoA, producing ATP, NADH, and FADH2.