Gamma-glutamyltransferase

Gamma-glutamyltransferase (also γ-glutamyltransferase, GGT, gamma-GT, gamma-glutamyl transpeptidase;

The name γ-glutamyltransferase is preferred by the Nomenclature Committee of the International Union of Biochemistry and Molecular Biology.^[5][2] The Expert Panel on Enzymes of the International Federation of Clinical Chemistry also used this name.^[6][2] The older name is gamma-glutamyl transpeptidase (GGTP).^[2]

Function

GGT is present in the

In prokaryotes and eukaryotes, GGT consists of two polypeptide chains, a heavy and a light subunit, processed from a single chain precursor by an autocatalytic cleavage.[12] The active site of GGT is known to be located in the light subunit.^{[citation needed]}

Co-translational

GGT is predominantly used as a diagnostic marker for liver disease.^{[citation needed]} Elevated serum GGT activity can be found in diseases of the liver, biliary system, pancreas and kidneys.^[13][14] Latent elevations in GGT are typically seen in patients with chronic viral hepatitis infections often taking 12 months or more to present.^{[citation needed]}

Individual test results should always be interpreted using the reference range from the laboratory that performed the test, though example reference ranges are 15–85 IU/L for men, and 5–55 IU/L for women.^[15] GGT is similar to alkaline phosphatase (ALP) in detecting disease of the biliary tract. Indeed, the two markers correlate well, though there are conflicting data about whether GGT has better sensitivity.^[16][17] In general, ALP is still the first test for biliary disease. The main value of GGT is in verifying that ALP elevations are, in fact, due to biliary disease; ALP can also be increased in certain bone diseases, but GGT is not.^[17]

Alcohol use

GGT is elevated by ingestion of large quantities of alcohol (needs reference) However, determination of high levels of total serum GGT activity is not specific to alcohol intoxication,^[18] and the measurement of selected serum forms of the enzyme offer more specific information.^[19] Isolated elevation or disproportionate elevation compared to other liver enzymes (such as ALT or alanine transaminase) can indicate harmful alcohol use or alcoholic liver disease,^[20] and can indicate excess alcohol consumption up to 3 or 4 weeks prior to the test.^{[citation needed]} The mechanism for this elevation is unclear. Alcohol might increase GGT production by inducing hepatic microsomal production, or it might cause the leakage of GGT from hepatocytes.^[21]

Xenobiotics

Numerous drugs can raise GGT levels, including

GGT is expressed in high levels in many different tumors. It is known to accelerate tumor growth and to increase resistance to cisplatin in tumors.[27]

Examples

Human proteins that belong to this family include