Prostate-specific antigen (PSA) is known to have an enzymatic function as a serine protease. It is produced exclusively by the epithelial cells of the acini and ducts of the prostate gland and is released into the lumina of the prostatic duct (see image on the right) where it acts to liquefy the seminal coagulum. PSA is produced in adult males by normal, benign, hyperplastic, and malignant prostate tissue, but not in any other human tissues.
Following its production from the acini and ducts, a small amount of PSA is uptaken by the capillary-rich prostate into the blood circulation, where it remains in circulation with a half-life of 3.2 days.2
The entire 240 amino acid residue sequence of PSA has been confirmed, along with its three-dimensional structure.2 Because its structure is so well characterized, specific antibodies against several of its antigenic epitopes have been developed, which has lead to several accurate immunoassays to detect its presence and quantitate its concentration in biological samples.