UNLABELLED Glutamate carboxypeptidaseIII (GCPIII) is best known as a homologue of glutamate carboxypeptidase II [GCPII; also known as prostate-specific membrane antigen (PSMA)], a protease involved in neurological disorders and overexpressed in a number of solid cancers. However, mouse GCPIII was recently shown to cleave β-citrylglutamate (BCG), suggesting that these two closely related enzymes have