[50] γ-Glutamyl transpeptidase from kidney

This chapter focuses on mammalian γ-glutamyl transpeptidase, emphasizing the rat kidney enzyme, the most extensively studied transpeptidase. γ-glutamyl transpeptidase plays a key role in the γ-glutamyl cycle, a pathway for the synthesis and degradation of glutathione. Glutathione is synthesized from its constituent amino acids within the cells by the successive actions of γ-glutamylcysteine and glutathione synthetases. The reactions allow the storage of cysteine as glutathione and γ-glutamyl transpeptidase catalyzes the first step in the pathway that leads to release of the cysteine moiety from the tripeptide. Homogenates of animal tissues exhibit a wide range of transpeptidase activity. Low transpeptidase activity in a tissue homogenate is often misleading because specific localization studies indicate that there are specific regions of intense enzyme activity in many tissues. In most mammals, the kidney exhibits by far the highest activity.