Alanine aminotransferase

Definition

Alanine aminotransferase (ALT) is an enzyme that plays a critical role in amino acid metabolism by catalyzing the transfer of an amino group from alanine to alpha-ketoglutarate, forming pyruvate and glutamate. This enzyme is vital for both amino acid catabolism and urea cycle processes, as it helps in the conversion of excess amino acids into intermediates that can enter metabolic pathways for energy production and nitrogen excretion.

5 Must Know Facts For Your Next Test

1. Alanine aminotransferase is predominantly found in the liver, making it a critical marker for liver health; elevated levels often indicate liver damage or disease.
2. ALT levels can also increase due to muscle injury, although its primary function is associated with hepatic metabolism.
3. The reaction catalyzed by alanine aminotransferase is reversible, which allows for flexibility in amino acid metabolism under varying physiological conditions.
4. In the context of the urea cycle, alanine serves as a source of nitrogen that can be incorporated into urea for safe excretion from the body.
5. Measuring ALT levels is a common clinical test used to assess liver function and diagnose liver-related disorders.

Review Questions

• How does alanine aminotransferase contribute to the process of transamination and what is its significance in amino acid metabolism?
  • Alanine aminotransferase facilitates transamination by transferring an amino group from alanine to alpha-ketoglutarate, resulting in the formation of pyruvate and glutamate. This process is crucial because it allows for the interconversion of amino acids and supports energy production by providing pyruvate as an entry point into the citric acid cycle. Without this enzyme, the balance of amino acids in the body would be disrupted, affecting overall metabolism.
• Discuss how elevated levels of alanine aminotransferase can indicate liver health and why monitoring this enzyme is important.
  • Elevated alanine aminotransferase levels are commonly associated with liver damage or disease since this enzyme is primarily located in the liver. When liver cells are damaged, ALT leaks into the bloodstream, leading to increased serum levels. Monitoring ALT levels is essential in clinical settings as it provides valuable insights into liver function and can help diagnose conditions such as hepatitis or fatty liver disease.
• Evaluate the role of alanine aminotransferase in linking amino acid catabolism to the urea cycle and its impact on nitrogen balance in the body.
  • Alanine aminotransferase plays a pivotal role in connecting amino acid catabolism to the urea cycle by providing nitrogen for urea synthesis. When excess amino acids are broken down, ALT helps convert alanine into pyruvate and glutamate, with glutamate serving as a nitrogen donor for urea production. This process is crucial for maintaining nitrogen balance, preventing ammonia toxicity, and ensuring that excess nitrogen from amino acid breakdown is efficiently excreted as urea through urine.

Related terms

Transamination:

The process by which an amino group is transferred from one amino acid to a keto acid, forming a new amino acid and a new keto acid.

Pyruvate:

A key intermediate in several metabolic pathways, formed from glucose during glycolysis and can be converted into acetyl-CoA or used for gluconeogenesis.

Urea Cycle:

A series of biochemical reactions in the liver that convert ammonia, a toxic byproduct of amino acid metabolism, into urea for excretion from the body.