Catalyzes the hydrolysis of the amide bond in N-(4-oxoglutarate)-L-cysteinylglycine (deaminated glutathione), a metabolite repair reaction to dispose of the harmful deaminated glutathione. Plays a role in cell growth and apoptosis. Has tumor suppressor properties that enhances the apoptotic responsiveness in cancer cells. It is also a negative regulator of primary T-cells. H2O + N-(4-oxoglutaryl)-L-cysteinylglycine = 2-oxoglutarate + L-cysteinylglycine Belongs to the carbon-nitrogen hydrolase superfamily. NIT1/NIT2 family.