Properties of γ-glutamyltransferase in developing rat brain

The activity and properties of brain γ-glutamyltransferase (EC 2.3,2.2) were studied in 7-, 14-and 90-day-old rats. The enzyme activity was highest in the pons-medulla and lowest in the cerebellum in each age group. The activity of glycylglycine, 10 protein amino acids, GABA and taurine as acceptor of the γ-glutamyl group was studied with 7-day-old and adult rats. The best acceptors were glycylglycine, lysine and methionine and the poorest taurine, valine and isoleucine. The relative acceptor activity of lysine changed most during development. Km for the γ-glutamyl donor, γ-glutamyl-p-nitroanilide, with glycylglycine was about 3 mM in all experimental groups. It did not change during development but V increased about fivefold in all brain areas studied. A mixture of serine and borate strongly inhibited γ-glutamyltransferase in each age group. Potassium and magnesium ions had no measurable effect on the enzyme activity but sodium ions were stimulatory.