Cleaves the gamma-glutamyl peptide bond of glutathione and glutathione-S-conjugate. Converts leukotriene C4 (LTC4), a glutathione-S-conjugate, to leukotriene D4 (LTD4). Does not cleave gamma-glutamyl compounds such as gamma-glutamyl leucine. May also catalyze a transpeptidation reaction in addition to the hydrolysis reaction, transferring the gamma-glutamyl moiety to an acceptor amino acid to form a new gamma-glutamyl compound. Acts as a negative regulator of geranylgeranyl glutathione bioactivity by cleaving off its gamma-glutamyl group, playing a role in adaptive immune responses. 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 H2O + leukotriene C4 = L-glutamate + leukotriene D4 H2O + S-[(2E,6E,10E)-geranylgeranyl]-L-glutathione = L-glutamate + S-[(2E,6E,10E)-geranylgeranyl]-L-cysteinylglycine Inhibited by serine-borate. Lipid metabolism; leukotriene D4 biosynthesis. Sulfur metabolism; glutathione metabolism. 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. Glycosylated. A previous study reported that GSH and oxidized glutathione (GSSG) are not substrates for murine GGT5 (By similarity). However, this result contrasts with two studies reported that GSH is indeed a substrate for GGT5 (By similarity). Belongs to the gamma-glutamyltransferase family.