Prostate-specific membrane antigen (PSMA) is a 100-120 kDa type II transmembrane glycoprotein that is a glutamate-preferring carboxy-peptidase. Three functionally distinct proteins are encoded, including folylpoly-gamma-glutamate carboxypeptidase in the intestine, N-acetylated alpha-linked acidic dipeptidase 1 in the brain, and prostate-specific membrane antigen in the prostate. PSMA is highly expressed in prostate secretory-acinar epithelium, in some benign extraprostatic epithelial cells from breast, duodenum, and kidney tissues, and in prostate cancer.