Catalyzes the cleavage of glutathione into 5-oxo-L-proline and a Cys-Gly dipeptide. Acts specifically on glutathione, but not on other gamma-glutamyl peptides. Glutathione depletion is an important factor for apoptosis initiation and execution. Acts as a pro-apoptotic component of the unfolded protein response pathway by mediating the pro-apoptotic effects of the ATF4-ATF3-DDIT3/CHOP cascade (By similarity). Negative regulator of Notch signaling pathway involved in embryonic neurogenesis: acts by inhibiting Notch cleavage by furin, maintaining Notch in an immature inactive form, thereby promoting neurogenesis in embryos (PubMed:22445366). glutathione = 5-oxo-L-proline + L-cysteinylglycine Interacts with NOTCH1 (via extracellular region). Widely expressed, with high expression in forebrain and anterior spinal cord. Expressed at intermediate level in the dorsal aorta and heart. Present throughout adult brain (at protein level). Belongs to the gamma-glutamylcyclotransferase family. ChaC subfamily.