Aspartate transaminase

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Aspartate aminotransferase reaction

Gallus gallus aspartate aminotransferase dimer

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Aspartate aminotransferase mechanism

Aspartate transaminase (AST), also known as aspartate aminotransferase or serum glutamic-oxaloacetic transaminase (SGOT), is an enzyme that plays a key role in amino acid metabolism. It is found in various tissues throughout the body, with high concentrations in the liver, heart, muscles, kidneys, and brain. AST catalyzes the reversible transfer of an amino group from aspartate to alpha-ketoglutarate, producing glutamate and oxaloacetate as products. This reaction is a critical step in the urea cycle and the citric acid cycle (Krebs cycle), which are essential for the detoxification of ammonia and the production of energy in cells, respectively.

Function

AST is involved in the metabolism of amino acids, which are the building blocks of proteins. By transferring amino groups, AST plays a crucial role in the synthesis and breakdown of amino acids and in the production of energy. The enzyme's activity is not limited to the liver; it also participates in metabolic processes in the heart, muscles, kidneys, and brain, reflecting its importance in the overall metabolic function of the body.

Clinical Significance

The measurement of AST levels in the blood is a common component of liver function tests. Elevated levels of AST can indicate damage to cells containing the enzyme, most often the liver but also the heart, muscles, or other tissues. Conditions that can lead to elevated AST levels include hepatitis, cirrhosis, myocardial infarction (heart attack), and muscular dystrophy. However, since AST is present in multiple tissues, it is usually measured alongside alanine transaminase (ALT), an enzyme predominantly found in the liver, to better assess liver damage.

Diagnostic Use

In clinical practice, the AST to ALT ratio is often used to differentiate between causes of liver damage. A ratio greater than 1 may indicate alcoholic liver disease, while a lower ratio might suggest non-alcoholic causes. However, these tests are not definitive on their own and are usually part of a comprehensive evaluation that includes other biochemical tests, imaging studies, and clinical assessment.

Pathology

Elevated AST levels can be found in a variety of pathological conditions beyond liver disease, such as acute pancreatitis, acute renal failure, and hemolytic anemia. In cases of myocardial infarction, AST levels can rise within 6-10 hours after the onset of chest pain, reaching a peak at 24-48 hours and returning to normal within 3-5 days. Thus, AST can serve as a marker for tissue damage, although it is not specific to any single condition.

Conclusion

Aspartate transaminase is a vital enzyme in amino acid metabolism and energy production. Its measurement is an important tool in diagnosing and monitoring various diseases, particularly those affecting the liver. However, due to its wide tissue distribution, elevated AST levels must be interpreted in conjunction with other diagnostic tests and clinical information.