The Emerging Roles of Glutamyl Peptides Produced by Glutamyltransferase and the Glutathione Synthesis System Glutamyl Cycle Crystal structures of glutamyltranspeptidase from Escherichia coli, a key enzyme in glutathione metabolism, and its reaction intermediate PNAS Critical Roles of the CysteineGlutathione Axis in the Production of Glutamyl Peptides in the Nervous System Targeting gamma glutamyl transpeptidase: A pleiotropic enzyme involved in glutathione metabolism and in the control of redox homeostasis ScienceDirect