300 ONTOGENESIS OF GAMMA-GLUTAMYL TRANSPEPTIDASE (GGTP) IN RAT TISSUES

Abstract

One of the mechanisms for amino acid active transport into the cell is GGTP. In order to map its developmental patterns this enzyme was studied in Wistar rat tissues before and after birth. Glycylglycine was the acceptor and L-δ-glutamyl-p-nitroanilide the donor in the assays. Placental GGTP activity (as nmoles/min × mg protein) decreased from 2.06 ± 0.15 to 0.69 ± 0.07) between the 14th and 21st day of gestation. Fetal kidney GGTP had the highest mean sp. act. than any other tissue at every stage of development. It doubled from the 20th day of gestation to birth (200 to 409), and then increased to 1,452 at 21 d. of age. GGTP in the small intestinal mucosa reached a peak by the middle of the lactation period (106 at 12 d. of age), returning to lower, fetal levels (22) at three weeks of age. Brain GGTP was minimal in utero (2.8 at the 20th day of gestation), and fell to zero at birth, increasing again during lactation and adulthood. Liver GGTP was measurable only in the gestational period, but after birth it became almost negligible. These data suggest that GGTP may play a role in amino acid transport into cells of various tissues in the later part of gestation. After birth, the only organ with significant GGTP activity is the kidney, where its physiologic role has been well studied (Supported in part by USPHS NIH grant S08 RR-09128-02).