This is a bifunctional protein that also has the activity of EC 126.96.36.199, gamma-glutamyltransferase. The enzyme binds its substrate by forming an initial gamma-glutamyl-enzyme intermediate, releasing the L-cysteinylglycine part of the molecule. The enzyme then reacts with either a water molecule or a different acceptor substrate (usually an L-amino acid or a dipeptide) to form L-glutamate or a product containing a new gamma-glutamyl isopeptide bond, respectively. The enzyme acts on glutathione, glutathione-S-conjugates, and, at a lower level, on other substrates with an N-terminal L-gamma-glutamyl residue. It plays a crucial part in the glutathione-mediated xenobiotic detoxification pathway. The enzyme consists of two chains that are created by the proteolytic cleavage of a single precursor polypeptide.