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. Interacts with TLCD3A. Heterodimer composed of the light and heavy chains. The active site is located in the light chain. Widely expressed, but at low level, except in the airway epithelial cells. Detected in brain, heart, kidney, liver, lung, spleen, testis and trachea. Cleaved by autocatalysis into a large and a small subunit and the autocatalytic cleavage is essential to the functional activation of the enzyme. Belongs to the gamma-glutamyltransferase family. Extended N-terminus.