Subcellular localization of gamma-glutamyltransferase activity in guinea pig liver. Effect of phenobarbital on the enzyme activity levels

Clinica Chimica Acta; International Journal of Clinical Chemistry
N E Huseby

Abstract

The localization of gamma-glutamyltransferase activity in guinea pig liver was studied after subcellular fractionation. The enzyme activity was essentially connected with plasma membranes whereas only low activity was found in the endoplasmic reticulum. A similar activity distribution was demonstrated for 5'-nucleotidase. Highest specific activity of gamma-glutamyltransferase was found in plasma membranes enriched in bile canaliculi. In this fraction the specific activity was 35 times greater than the specific activity of the total homogenate, a value similar to the relative specific activity of (Na+,K+)-ATPase. More than 90% of the total gamma-glutamyltransferase activity in guinea pig liver was connected with parenchymal cells and the enzyme seemed to have an outside orientation. Animals treated with phenobarbital showed moderate increased in gamma-glutamyltransferase activity in serum and liver, whereas high activities were found in most bile samples. No particular liver subfraction showed substantial accumulation of gamma-glutamyltransferase activity. The present findings do not support the suggested use of serum gamma-glutamyltransferase measurements as a direct index of "microsomal enzyme induction".

References

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Related Concepts

Establishment and Maintenance of Localization
Adenosine Triphosphatases
Cavia
Gamma-glutamyl transferase
Gamma Glutamyl Transferase Measurement
Cell Nucleus
Gamma-glutamyltransferase Activity
Subcellular Fractionation
Microsomes, Liver
Phenobarbital

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