Gamma glutamyl transferase: application of a new radiochemical assay to the analysis of its subcellular distribution in the rat liver.

gamma-Glutamyl transferase (gamma-GT) is a key catalyst in the metabolism of glutathione. Its activity in the rat liver is usually very low but it increases significantly during the process of chemical hepatocarcinogenesis. A new radiochemical assay is reported which measures the amount of 3H-aniline liberated from gamma-glutamyl-3H-anilide. This assay is highly specific and no biological substances interferes. By applying this new assay to the analysis of the subcellular distribution of the rat liver gamma-GT, it is shown that it distributes between two pools, one which corresponds to a membrane-bound enzyme, the other to a soluble enzyme. The subcellular distribution of gamma-GT is discussed by comparison with the patterns of distribution of classical marker enzymes.