Cleaves the gamma-glutamyl bond of extracellular glutathione (gamma-Glu-Cys-Gly), glutathione conjugates, and other gamma-glutamyl compounds. The metabolism of glutathione releases free glutamate and the dipeptide cysteinyl-glycine, which is hydrolyzed to cysteine and glycine by dipeptidases. Uses glutamine as a gamma-glutamyl donor and acceptor for gamma-polyglutamic acid synthesis. Dipeptides are better gamma-glutamyl acceptors than free amino acids (PubMed:1371053). an alpha-amino acid + an N-terminal (5-L-glutamyl)-[peptide] = 5-L-glutamyl amino acid + N-terminal L-alpha-aminoacyl-[peptide] glutathione + H2O = L-cysteinylglycine + L-glutamate an S-substituted glutathione + H2O = an S-substituted L-cysteinylglycine + L-glutamate Inhibited by glucose. Optimum pH is 8.0-8.5 for transfer of p-nitroanilide from gamma-glutamyl-p-nitroanilide (gamma-GpNA) to glycylglycine (gly-gly). Optimum temperature is 60 degrees Celsius. Sulfur metabolism; glutathione metabolism. This enzyme consists of two polypeptide chains, which are synthesized in precursor form from a single polypeptide. Cleaved by autocatalysis into a large and small subunit. Belongs to the gamma-glutamyltransferase family.