In enzymology, a glutathione gamma-glutamylcysteinyltransferase () is an enzyme that catalyzes the chemical reaction
Thus, the two substrates of this enzyme are glutathione and [Glu(-Cys)]n-Gly, whereas its two products are Gly and [Glu(-Cys)]n+1-Gly.
This enzyme belongs to the family of transferases, specifically the aminoacyltransferases. The systematic name of this enzyme class is glutathione:poly(4-glutamyl-cysteinyl)glycine 4-glutamylcysteinyltransferase. Other names in common use include phytochelatin synthase, and gamma-glutamylcysteine dipeptidyl transpeptidase.
As of late 2007, two structures have been solved for this class of enzymes, with PDB accession codes and .