Hydrolyzes deaminated glutathione (dGSH) to 2-oxoglutarate and L-cysteinylglycine, and no activity on glutathione or L-glutamine. May function as a metabolite repair enzyme. H2O + N-(4-oxoglutaryl)-L-cysteinylglycine = 2-oxoglutarate + L-cysteinylglycine Belongs to the carbon-nitrogen hydrolase superfamily. NIT1/NIT2 family. Truncated N-terminus.