Glutamate carboxypeptidase III (GCPIII) is a metalloenzyme that belongs to the transferrin receptor⁄glutamate carboxypeptidase II (GCPII; EC ) superfamily. GCPIII has been studied mainly because of its evo-lutionary relationship to GCPII, an enzyme involved in a variety of neuro-pathologies and malignancies, such as glutamatergic neurotoxicity and prostate cancer.