Involved in glucosinolate biosynthesis. Hydrolyzes the gamma-glutamyl peptide bond of several glutathione (GSH) conjugates to produce Cys-Gly conjugates related to glucosinolates. The gamma-Glu-Cys-Gly-GSH conjugates are the sulfur-donating molecule in glucosinolate biosynthesis. Can use the GSH conjugate of the camalexin intermediate IAN (GS-IAN) as substrate. Required for the biosynthesis of camalexin, a pathogen-inducible phytoalexin with antibacterial and antifungal properties. an S-[(1E)-1-(hydroxyimino)-omega-(methylsulfanyl)alkyl]-L-glutathione + H2O = an S-[(1E)-1-(hydroxyimino)-omega-(methylsulfanyl)alkyl]-L-cysteinylglycine + L-glutamate (E)-1-(glutathione-S-yl)-2-(1H-indol-3-yl)acetohydroximate + H2O = (E)-1-(glycyl-L-cystein-S-yl)-2-(1H-indol-3-yl)acetohydroximate + L-glutamate 2-(glutathion-S-yl)-2-(1H-indol-3-yl)acetonitrile + H2O = 2-(glycyl-L-cystein-S-yl)-2-(1H-indol-3-yl)acetonitrile + L-glutamate (Z)-1-(glutathione-S-yl)-2-phenylacetohydroximate + H2O = (Z)-1-(glycyl-L-cystein-S-yl)-2-phenylacetohydroximate + L-glutamate Secondary metabolite biosynthesis. Belongs to the peptidase C26 family.