A characterization of γ-glutamyltranspeptidase in normal, perinatal, premalignant and malignant rat liver

Abstract

1. 1. γ-Glutamyltranspeptidase displays the following order of activity in tissues of the Fischer 344 rat: kidney ⪢ small intestine ⪢ cerebral cortex = testis > lung ⪢ liver = heart. 2. 2. The activity of the hepatic enzyme in rats is: 4-fold higher in females than males; 4-fold higher in male Wistar, Sprague-Dawley and Zucker rats than male Fischer 344 rats; increased 10-fold in very old vs young male Fischer 344. 3. 3. The hepatic enzyme displays significant species variation: the mouse and rat liver enzymes are similar and low in activity, while duck, dog, pig and beef enzymes are 7, 13, 86 and 92-fold higher, respectively, in activity than the male Fischer rat liver enzyme. 4. 4. A liver plasma membrane isolation procedure has been devised which selects for the sinusoidal face of the liver parenchymal cell as assessed by marker enzyme analysis: for these plasma membranes the purification of γ-glutamyltranspeptidase is 21.5 and the recovery is 42% and the recovery indicating that this is the cellular and subcellular locus of the enzyme in rat liver. 5. 5. The characteristics of the liver plasma membrane from female rats are: pH optimum of 8.0; classical Michaelis-Menten kinetics; K m of 1.43 mM and V max of 33.3 nmol·mg −1·min −1. 6. 6. In Fischer 344 rats, γ-glutamyltranspeptidase activities are elevated over adult levels in perinatal liver: in fetal liver homogenates and plasma membranes the activities are increased 179 and 109-fold, respectively. The activity peaks just after birth and declines rapidly over the first 15 postnatal days. 7. 7. The activity of the liver enzyme in the male Fischer 344 rat exhibits a progressive increase throughout diethylnitrosamine-induced hepatocarcinogenesis: it is increased 7.8-fold in homogenates and 5.4-fold in plasma membranes at the early premalignant stage; 74-fold in homogenates and 31-fold in plasma membranes at the later hyperplastic nodular premalignant stage; and 174-fold in homogenates and 61-fold in plasma membranes at the hepatoma stage. The gradual drop in purification during hepatocarcinogenesis is associated with the appearance of the enzyme in the blood.