Glycine—oxaloacetate transaminase

Glycine—oxaloacetate transaminase (GOT), also known as aspartate aminotransferase (AST) or serum glutamic-oxaloacetic transaminase (SGOT), is an enzyme that plays a key role in amino acid metabolism and the urea and citric acid cycles. This enzyme catalyzes the reversible transfer of an amino group from aspartate to alpha-ketoglutarate, producing oxaloacetate and glutamate. GOT is found in various tissues, including the liver, heart, skeletal muscle, kidneys, brain, and red blood cells, reflecting its essential role in nitrogen metabolism and energy production.

Function

GOT is involved in the catabolism and synthesis of amino acids, which are the building blocks of proteins. This enzyme facilitates the conversion of aspartate and alpha-ketoglutarate to oxaloacetate and glutamate, respectively. This reaction is crucial for the deamination of amino acids, necessary for their use in energy production and the synthesis of other compounds. GOT plays a significant role in the malate-aspartate shuttle, which is essential for transferring reducing equivalents from the cytosol to the mitochondria, thereby supporting cellular respiration and energy production.

Clinical Significance

Elevated levels of GOT in the blood are an indicator of tissue damage, particularly in the liver, heart, and muscles. As such, GOT is commonly measured in diagnostic blood tests as part of liver function tests and to assess myocardial infarction (heart attack). In liver diseases such as hepatitis and cirrhosis, or in conditions like myocardial infarction, the damaged cells release GOT into the bloodstream, leading to elevated serum levels. Therefore, the measurement of GOT, often in conjunction with alanine aminotransferase (ALT), can help in diagnosing and monitoring the progression of these conditions.

Isoenzymes

GOT exists in two isoenzymes: GOT1 (or AST1), located in the cytoplasm, and GOT2 (or AST2), located in the mitochondria. The differential distribution of these isoenzymes in tissues is used in clinical diagnostics to determine the source of tissue damage. For example, a higher ratio of GOT to ALT in the blood may suggest alcoholic liver disease, whereas a lower ratio could indicate non-alcoholic fatty liver disease.

Genetics

The genes encoding the two isoenzymes of GOT are located on different chromosomes: GOT1 on chromosome 10 and GOT2 on chromosome 16. Mutations in these genes are rare but can affect the enzyme's function and stability, potentially leading to metabolic disorders.

See Also

• Alanine aminotransferase
• Liver function tests
• Myocardial infarction
• Metabolic pathway