Hydrolyzes and transfers gamma-glutamyl moieties from glutathione and other gamma-glutamyl compounds to acceptors. 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 Sulfur metabolism; glutathione metabolism. Cleaved by autocatalysis into a large and a small subunit. Belongs to the gamma-glutamyltransferase family. Could be the product of a pseudogene.