Alanine—oxo-acid Transaminase

Alanine—oxo-acid transaminase, also known as alanine aminotransferase (ALT) or serum glutamate-pyruvate transaminase (SGPT), is an enzyme that plays a crucial role in the metabolism of amino acids and glucose. It catalyzes the transfer of an amino group from alanine to alpha-ketoglutarate, producing pyruvate and glutamate as a result. This reaction is reversible and is a key step in the interconversion of amino acids and carbohydrates, which occurs primarily in the liver but also in the kidney and muscle tissues.

Function

The primary function of alanine—oxo-acid transaminase is to facilitate the conversion of alanine, one of the most abundant amino acids in the blood, into pyruvate, which can then enter the gluconeogenesis pathway to produce glucose, or the Krebs cycle to be used as energy. This enzyme's activity is vital for maintaining the body's energy balance, especially during fasting, strenuous exercise, or any condition that requires an increased energy supply.

Clinical Significance

Elevated levels of alanine—oxo-acid transaminase in the blood are an indicator of liver damage or inflammation, as this enzyme is released into the bloodstream when liver cells are damaged. Therefore, ALT levels are commonly measured in blood tests as part of liver function tests to diagnose and monitor liver diseases such as hepatitis, cirrhosis, and liver cancer. It is also used to monitor the progression of disease or the response to treatment in individuals with liver conditions.

Structure

Alanine—oxo-acid transaminase is a pyridoxal phosphate (PLP)-dependent enzyme. The PLP molecule serves as a coenzyme and is essential for the enzyme's catalytic activity. The enzyme exists in various isoforms, which may differ in terms of their kinetic properties and tissue distribution.

Diagnostic Use

The measurement of ALT levels is a routine part of blood tests aimed at evaluating liver health. An ALT test is often performed alongside an aspartate aminotransferase (AST) test. The AST/ALT ratio is a useful diagnostic indicator; for example, a ratio greater than 1 is suggestive of alcoholic liver disease, while a lower ratio may indicate non-alcoholic fatty liver disease or hepatitis.

Pathophysiology

Alterations in alanine—oxo-acid transaminase activity can have significant metabolic consequences. For instance, in liver diseases, the impaired function of ALT can disrupt the balance between amino acid and carbohydrate metabolism, leading to metabolic disturbances. Additionally, since ALT is involved in amino acid metabolism, abnormalities in its activity can affect protein synthesis and degradation.

Treatment and Management

Treatment of elevated ALT levels focuses on addressing the underlying cause of the liver damage. This may involve lifestyle changes, such as diet and exercise, medication to treat the specific liver condition, or in severe cases, liver transplantation. Monitoring ALT levels is crucial in assessing the effectiveness of the treatment regimen and the progression of liver disease.

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