Cleaves the gamma-glutamyl peptide bond of glutathione and glutathione-S-conjugate (By similarity). Converts leukotriene C4 (LTC4), a glutathione-S-conjugate, to leukotriene D4 (LTD4) (PubMed:9774450, PubMed:11463821, PubMed:12163373). Does not cleaves 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 (By similarity). 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 (PubMed:12163373). The active site is located in the light chain (By similarity). Very low level of expression. Detected in spleen lymphocytes, medullary and paracortical thymic lymphocytes, lung interstitial cells, bronchial epithelium, proximal tubules in kidney, crypt cells in small intestine, neurons in brain stem and cerebral cortex and in Purkinje cells. Very low expression. Cleaved by autocatalysis into a large and a small subunit. Glycosylated. Deficient mice shown no obvious phenotype but in most organs they have only 10% of the wild-type levels of gamma-glutamyl leukotrienase activity (PubMed:11463821). Mice deficient in GGT5 have significantly more airway hyper-reactivity in a model of experimental asthma (PubMed:12163373). A previous study reported that GSH and oxidized glutathione (GSSG) are not substrates for murine GGT5 (PubMed:9774450). However, this result contrasts with two studies reported that GSH is indeed a substrate for GGT5 (By similarity). Belongs to the gamma-glutamyltransferase family.