Aspartate transaminase

Definition

Aspartate transaminase (AST) is an enzyme that catalyzes the transfer of an amino group from aspartate to α-ketoglutarate, resulting in the production of oxaloacetate and glutamate. This enzyme plays a vital role in amino acid metabolism and gluconeogenesis, connecting amino acid biosynthesis with energy production processes in the cell.

5 Must Know Facts For Your Next Test

1. Aspartate transaminase is found in various tissues, with particularly high concentrations in the liver and heart, making it a useful marker for tissue damage.
2. Elevated levels of AST can indicate liver disease, myocardial infarction, or other conditions causing cellular injury.
3. The reaction catalyzed by aspartate transaminase is reversible, allowing for the interconversion of amino acids and their corresponding keto acids.
4. In addition to its role in amino acid metabolism, AST is involved in the urea cycle, contributing to the detoxification of ammonia.
5. AST functions alongside alanine transaminase (ALT) as part of the aspartate-argininosuccinate pathway, which is essential for maintaining nitrogen balance.

Review Questions

• How does aspartate transaminase contribute to both amino acid metabolism and gluconeogenesis?
  • Aspartate transaminase plays a critical role in amino acid metabolism by facilitating the transfer of an amino group from aspartate to α-ketoglutarate. This reaction produces oxaloacetate and glutamate, which not only helps in synthesizing other amino acids but also links to gluconeogenesis. By generating oxaloacetate, AST contributes to the production of glucose from non-carbohydrate sources during fasting or low-carbohydrate intake.
• Discuss the clinical significance of measuring aspartate transaminase levels in patients.
  • Measuring aspartate transaminase levels is clinically significant as elevated levels can indicate tissue damage, particularly in the liver and heart. Conditions such as hepatitis, liver cirrhosis, and myocardial infarction are often associated with increased AST activity. Monitoring AST levels helps healthcare providers assess the extent of organ damage and guide treatment decisions, making it a valuable biomarker in clinical practice.
• Evaluate how the reversible nature of the reaction catalyzed by aspartate transaminase affects metabolic pathways involving amino acids.
  • The reversible nature of the reaction catalyzed by aspartate transaminase allows for flexibility in metabolic pathways involving amino acids. When there is an abundance of substrates, the enzyme can facilitate the conversion of aspartate to oxaloacetate and glutamate. Conversely, when amino acids are needed for protein synthesis or energy production, the reaction can shift to produce more aspartate from oxaloacetate and glutamate. This dynamic regulation ensures that the body maintains a proper balance of amino acids and supports various metabolic processes depending on physiological needs.

Related terms

Amino Acid Metabolism: The set of biochemical processes responsible for the synthesis and breakdown of amino acids in the body.

Transamination:

A chemical reaction that transfers an amino group from one amino acid to a keto acid, facilitating amino acid interconversion.

α-Ketoglutarate: A key intermediate in the Krebs cycle that acts as an acceptor of amino groups in transamination reactions.