Propionyl-CoA Carboxylase

Definition

Propionyl-CoA carboxylase is an enzyme complex that catalyzes the carboxylation of propionyl-CoA to form D-methylmalonyl-CoA, an important step in the catabolism of certain amino acids, odd-chain fatty acids, and cholesterol. This enzyme plays a crucial role in the breakdown of triacylglycerols through the process of β-oxidation.

5 Must Know Facts For Your Next Test

1. Propionyl-CoA carboxylase is a biotin-dependent enzyme complex that requires the cofactor vitamin B12 (cobalamin) for its activity.
2. The carboxylation reaction catalyzed by propionyl-CoA carboxylase is an anaplerotic reaction, replenishing the citric acid cycle intermediates.
3. Deficiencies in propionyl-CoA carboxylase or its cofactors can lead to the accumulation of propionyl-CoA and methylmalonic acid, causing the metabolic disorder propionic acidemia.
4. In the context of triacylglycerol catabolism, propionyl-CoA carboxylase is involved in the breakdown of odd-chain fatty acids released during β-oxidation.
5. The D-methylmalonyl-CoA produced by propionyl-CoA carboxylase is then converted to succinyl-CoA, which can enter the citric acid cycle to generate ATP.

Review Questions

• Describe the role of propionyl-CoA carboxylase in the catabolism of triacylglycerols.
  • Propionyl-CoA carboxylase plays a crucial role in the catabolism of triacylglycerols through the process of β-oxidation. During β-oxidation, odd-chain fatty acids are broken down, resulting in the formation of propionyl-CoA. Propionyl-CoA carboxylase then catalyzes the carboxylation of propionyl-CoA to form D-methylmalonyl-CoA, which is subsequently converted to succinyl-CoA and enters the citric acid cycle. This enzyme helps to ensure the efficient breakdown and utilization of all components of triacylglycerols for energy production.
• Explain the importance of the cofactors required by propionyl-CoA carboxylase and the consequences of their deficiency.
  • Propionyl-CoA carboxylase requires the cofactors biotin and vitamin B12 (cobalamin) for its proper function. Biotin is essential for the carboxylation reaction, while vitamin B12 is necessary for the subsequent conversion of D-methylmalonyl-CoA to succinyl-CoA. Deficiencies in either of these cofactors can lead to the accumulation of propionyl-CoA and methylmalonic acid, resulting in the metabolic disorder propionic acidemia. This condition is characterized by the buildup of toxic metabolites, which can cause developmental delays, seizures, and other serious health problems. The importance of maintaining adequate levels of these cofactors highlights the critical role of propionyl-CoA carboxylase in maintaining proper metabolic function.
• Analyze the significance of the anaplerotic reaction catalyzed by propionyl-CoA carboxylase and its impact on the citric acid cycle.
  • The carboxylation reaction catalyzed by propionyl-CoA carboxylase is considered an anaplerotic reaction, meaning it replenishes intermediates in the citric acid cycle. The product of this reaction, D-methylmalonyl-CoA, is subsequently converted to succinyl-CoA, which can then enter the citric acid cycle. This is particularly important in the context of triacylglycerol catabolism, as the breakdown of odd-chain fatty acids can lead to the depletion of citric acid cycle intermediates. By providing succinyl-CoA, propionyl-CoA carboxylase helps to maintain the proper functioning of the citric acid cycle, ensuring the efficient generation of ATP from the products of triacylglycerol breakdown. This anaplerotic role of the enzyme highlights its significance in sustaining energy production and overall metabolic homeostasis.

Related terms

Propionyl-CoA: An acyl-CoA derivative formed during the breakdown of certain amino acids, odd-chain fatty acids, and cholesterol, which serves as a substrate for propionyl-CoA carboxylase.

D-Methylmalonyl-CoA: The product of the propionyl-CoA carboxylase reaction, which is then converted to succinyl-CoA and enters the citric acid cycle.

β-Oxidation: The catabolic process by which fatty acids are broken down to generate acetyl-CoA, which can then enter the citric acid cycle to produce ATP.