gamma-Glutamyltranspeptidase in liver homogenates of rats of different ages: enzyme kinetics and age course of Km and Vmax.

Optimum incubation conditions for the determination of gamma-glutamyltranspeptidase with liver homogenates from rats of different ages have been determined: about 1 mg protein/assay, 4.4 mM L-gamma-glutamyl-p-nitroanilide, 40 mM glycylglycine, 9.6 mM MgCl2 in 0.1 M Tris-HCl buffer, pH 8.0; final volume 1.3 ml. The enzyme activity is very high at birth, the increase before birth is not continuous. After birth the enzyme activity decreases quickly over the first postnatal days. The ENDRENYI-KWONG-plot was linear with homogenates from newborn and 3-day-old animals. For all other age groups the graphs showed an angle. Statistical analysis carried out that a two-enzyme model plots the experimental data only insignificantly better than a one-enzyme model. It may be concluded that there are different GGT isozymes which show different affinities towards the substrate and which show different developmental patterns.