Gamma-glutamyl transpeptidase

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Identifiers
EC number	2.3.2.2
CAS number	85876-02-4
Alt. names
IntEnz	IntEnz view
BRENDA	BRENDA entry
ExPASy	NiceZyme view
KEGG	KEGG entry
MetaCyc	metabolic pathway

Gamma-glutamyl transpeptidase (GGT or GGTP) is an enzyme that plays a critical role in the metabolism of glutathione and the transfer of amino acids and peptides across the cellular membrane. This enzyme is involved in the glutathione metabolism, antioxidant defense, and the detoxification of xenobiotics. GGT is also used as a diagnostic marker for various diseases, particularly liver and biliary diseases.

Structure

Gamma-glutamyl transpeptidase is a heterodimeric enzyme consisting of a large and a small subunit, which are encoded by different genes. The active site, which is responsible for the enzyme's catalytic activity, is located on the large subunit. The enzyme is anchored to the cell membranes of cells that line the biliary tract, kidney, and pancreas.

Function

The primary function of GGT is to transfer gamma-glutamyl functional groups from molecules such as glutathione to an acceptor that may be an amino acid, a peptide, or water. This process is crucial for the cleavage and resynthesis of glutathione, which is a key antioxidant in cellular defense against oxidative stress. By maintaining glutathione levels, GGT plays a role in protecting cells from oxidative stress and maintaining cellular redox balance.

Clinical significance

Elevated levels of GGT in the blood are commonly associated with liver diseases, including hepatitis, cirrhosis, and liver tumors. It is also elevated in cases of biliary obstruction. Because of its association with liver function, GGT is routinely measured in blood tests as a marker of liver health and function. Additionally, high GGT levels can be indicative of excessive alcohol consumption or use of certain drugs that are toxic to the liver.

Diagnostic use

In the clinical setting, GGT testing is used to diagnose and monitor diseases related to the liver and bile ducts. It is particularly useful in distinguishing between hepatic and bone disease when other enzymes such as alkaline phosphatase (ALP) are elevated, as GGT is not significantly raised in bone diseases.

See also

• Liver function tests
• Glutathione
• Enzyme